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Offline DSatz

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The myth of unity gain
« on: December 25, 2011, 02:02:01 PM »
Hi. May I post a Christmas rant that I hope will help someone in the long run?

I just read a discussion thread in which someone advised a new user to keep the record level control on a certain recorder set higher than about 4 or 5, since that was that recorder's "unity gain" point, and lower settings might lead to overload distortion even if the meters were below 0 dB and the red lights weren't flashing.

Many people here give advice like that. The advice could well be OK in many cases. But in other cases it could be off by enough to make someone end up with an overloaded recording despite their best efforts to avoid it. To understand why I say that, please follow me through the following set of reasons which I've compulsively organized into three blocks of three statements each:
  • Nearly all recorders have active first-stage amplifiers at their inputs rather than passive, variable resistors.
  • Every active circuit has an input overload limit--a signal voltage high enough to force the circuit out of its linear range.
  • Thus there is nearly always some input voltage high enough that if it occurred, it would overload the recorder's input stage and cause distortion.
  • Recording level controls generally affect incoming signals only after those signals have passed through the input stage.
  • (Record level controls are misnamed; they really only control the voltage gain at one point in the recorder's signal path. Recording level is a function of the input voltage, the voltage gain set by the control, and the fixed gain in the rest of the recording circuitry.)
  • If distortion occurs in the input stage, the action of the recording level control will be too late to stop it. In that case your "record level" setting will only determine the level at which you record the distortion. You can set it so that the meters only go to -20 and the overload LEDs never come on; you'll still have distortion due to input overload.
  • If there is a certain voltage above which input stage overload will occur, then there must also be a setting of the record level control at which a signal having that voltage would reach exactly 0 dB (full scale) on the recorder's meters.
  • If you find yourself wanting to set the record level control any lower than that setting in order to avoid reaching 0 dB on the meters, you probably have an input overload problem that needs a separate solution.
  • Thus it's well worth knowing what that control setting is for any recorder that you're using.
However (and this is my point), that setting of the record level control has nothing directly to do with the so-called "unity gain" setting of the device. The two things are independent and can very well differ from one another. I don't have any specific examples but in a given instance, setting a recorder's level control to its "unity gain" setting could still allow input overload to occur before 0 dB (full scale) is reached and before the "overload" indicators come on. Thus if you tell someone that the "unity gain" setting is the lowest safe setting, you may be giving them a false sense of safety.

The only reliable way to find the lowest safe setting is first to find the actual input overload point with a signal generator--then feed that level of signal (or just slightly below it) in to the recorder and observe the level setting at which 0 dB is reached on the meter. That's the safe setting limit for the control on that recorder. The voltage that happens to appear at the line level outputs of the recorder at that point is irrelevant; it may be similar to, or it may be higher than or lower than the voltage being fed in.

I urge everyone who refers to "unity gain" in this context to stop doing so, and replace the concept in your thinking with what really goes on.

--best regards
« Last Edit: December 25, 2011, 03:19:03 PM by DSatz »
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Re: The myth of unity gain
« Reply #1 on: December 25, 2011, 03:11:13 PM »
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Re: The myth of unity gain
« Reply #2 on: December 25, 2011, 03:51:24 PM »
Good explanation. Your rants are always a great source of information.
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Re: The myth of unity gain
« Reply #3 on: December 25, 2011, 06:05:02 PM »
Good explanation. Your rants are always a great source of information.
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Re: The myth of unity gain
« Reply #4 on: December 25, 2011, 07:03:00 PM »
Good explanation. Your rants are always a great source of information.

I had trouble understanding most of it tho :P ;D
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Offline flipp

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Re: The myth of unity gain
« Reply #5 on: December 25, 2011, 08:53:31 PM »
Happy to read your Christmas rant. I think it ties in nicely with this post you made earlier this year, particularly the final paragraph; and also from earlier this year - this post.

Like Bean, I don't always understand everything you mention in your posts, and sometimes almost nothing. In those cases you provide the seed for me to do further exploration/research.
« Last Edit: December 25, 2011, 09:53:54 PM by flipp »

stevetoney

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Re: The myth of unity gain
« Reply #6 on: December 25, 2011, 10:08:43 PM »
Many people here give advice like that. The advice could well be OK in many cases. But in other cases it could be off by enough to make someone end up with an overloaded recording despite their best efforts to avoid it.

I also don't understand your post.  However, my response is not to debate your post on technical merit.  I think you're missing the point of how people, for better or worse, are applying the unity gain term.

Unity gain, as presented in the discsussions I've read elsewhere, is a concept that's only a rule of thumb or guideline to help people understand how to better set their record levels.  I find that the concept is really useful to help to understand on a macro level the concepts, but it particularly helps out noobs in terms that are understandable and once noobs DO understand, they have a much higher success rate for getting good recordings. 

Thus if you tell someone that the "unity gain" setting is the lowest safe setting, you may be giving them a false sense of safety.

I think that your explanation, which I don't get, overcomplicates a simple concept which IMHO, for 99% of users, doesn't need any technical elaboration.  If I use a Sony M10 and it overloads at a loud rock show with a setting of 4, then the next time I set it at 3.  If my explanation for the distortion was that my setting was above 'unity gain', whether technically accurate or not, why does it matter?
 
The only reliable way to find the lowest safe setting is first to find the actual input overload point with a signal generator--

Really?  Who has access to a signal generator?  Not to be cynical, but why would I bother and why do I care? 

If my recordings never break up at 3 but they do at 4, then I know to set it at 3 because 3 is probably below the 'unity gain' point. 

Perhaps people are using some poetic license then if they were to call '4' the unity gain point because they haven't done the bench testing you suggest, but really why is that such a big deal in the context it's been used?


I hope I don't come off as a jerk with my responses above, but I'm just not getting your points about why the concept of unity gain, as it's been used here in the past, is a myth and why it's not valid.

Offline Will_S

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Re: The myth of unity gain
« Reply #7 on: December 25, 2011, 10:28:37 PM »
Many people here give advice like that. The advice could well be OK in many cases. But in other cases it could be off by enough to make someone end up with an overloaded recording despite their best efforts to avoid it.

I also don't understand your post.  However, my response is not to debate your post on technical merit.  I think you're missing the point of how people, for better or worse, are applying the unity gain term.

I believe his point is that what many folks call "unity gain" is not, in fact, unity gain. Nor is unity gain (as correctly defined) a particularly important thing for our purposes.  I thought most engineers were sticklers for correct terminology.   :D

I think that your explanation, which I don't get, overcomplicates a simple concept which IMHO, for 99% of users, doesn't need any technical elaboration.  If I use a Sony M10 and it overloads at a loud rock show with a setting of 4, then the next time I set it at 3.  If my explanation for the distortion was that my setting was above 'unity gain', whether technically accurate or not, why does it matter?

Why not just call it what it is - the minimum safe setting for the input level?  Rather than unity gain, that has an actual meaning, but that actual meaning is different.

Also, how do you know setting it at 3 next time will help?  Perhaps what you should be learning about your gear is that if the levels are too hot at 4, you need an external attenuator, turning it down to 3 won't help.  (This is arbitrary, I don't know what the safe level is on an M10.  But I do know that with a Tascam DR2D's mic in, if your levels are too hot at 67, don't bother turning it down to 60 - you need an external attenuator.)
 
The only reliable way to find the lowest safe setting is first to find the actual input overload point with a signal generator--

Really?  Who has access to a signal generator?  Not to be cynical, but why would I bother and why do I care?

Just about anybody reading this site has access to a signal generator.  Any decent audio editing software can generate all the test tones you could every need, and most of us have our computers set up for reasonable playback.  In terms of actual voltages, who cares indeed.  But it can be very useful to fire up a test tone (so you can very easily recognize distortion in the recorded wav file), send it into your recorder at various levels, and see at what input levels you can get an unclipped waveform back and what levels you can't, even if the recording meters aren't hitting "over" as you record.  (Do be aware though that some recorders can take hotter inputs than a lot of consumer gear can put out without clipping, so you do have to be sure you're overloading your recorder and not simply overdriving your source).

Quote
Perhaps people are using some poetic license then if they were to call '4' the unity gain point because they haven't done the bench testing you suggest, but really why is that such a big deal in the context it's been used?

I hope I don't come off as a jerk with my responses above, but I'm just not getting your points about why the concept of unity gain, as it's been used here in the past, is a myth and why it's not valid.

I think the problem is that people are conflating minimum safe input levels with "unity gain", where the output voltage is equal to the input voltage.  But what really matters for recording is making sure that you don't overload any intermediate stages hidden deep inside the recorder.  I agree that in practical terms it is not the actual numeric value of the voltage that matters - it's the record setting that is safe.  But that is not unity gain!

There also seems to be a myth that at the magical "unity gain" setting, you are bypassing all of the internal gain stages of the recorder and getting something purer.  With most consumer gear, that is not the case - there are usually gain stages that you just can't bypass, so there's nothing magical about unity gain on a typical digital pocket recorder.  The concern should be minimum safe input levels, and knowing that you will need an external attenuator if the incoming signal is too hot at those minimum levels. 

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Re: The myth of unity gain
« Reply #8 on: December 25, 2011, 11:00:51 PM »
^ Good response Will.  I understand your points and they for sure helps to explain David's initial points, I think.  If terminology could be better applied, then obviously I'm on board with that.  On the other hand, it seems as if the vernacular use of the term was serving a reasonable purpose, even if it wasn't being used with complete accuracy.  The bottom line of my earlier comment is that I know what most people here meant when they used the term.

« Last Edit: December 25, 2011, 11:15:17 PM by tonedeaf »

Offline Will_S

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Re: The myth of unity gain
« Reply #9 on: December 25, 2011, 11:28:57 PM »
^ Good response Will and it helps to explain David's initial point, I think.  If terminology could be better applied, then that's cool.  On the other hand, it seems as if the vernacular use of the term was serving a reasonable purpose, even if it wasn't being used with complete accuracy.  It's not my call one way or the other, but I know what most people mean when they use the term (up until now anyway ;)).

Right, and I agree that the bottom line is getting the right result.  But...

 I think in some cases people really were looking for true unity gain (I'll give an example in a second), and there were definitely cases of people writing the manufacturers and asking them what unity gain was for device XX.  Now if the manufacturer gave a response that was correct (for the correct definition of the term), that would not necessarily mean that folks could turn around and use that level as a safe minimum without running into trouble -- so it seems worth making sure that people are using the right terms to avoid disappointment down the line.

It's also problematic because folks were also looking for unity gain in another context - but as DSatz pointed out even then they may not really be getting what they were hoping for.

Remember when the Edirol R09 first came out?  All of a sudden there was a cool recorder with a respectable A/D converter and all kinds of other nice features, but only analog inputs and mediocre microphone preamps.  What was a V3>D8 taper to do without their trusty digital input?  The R09 offered so many obvious advantages over DAT, but how did you make the best use of the V3's better preamps when recording with the R09?  If you set the R09's input level "too high", you could still get decent levels by applying only a little gain with the V3, but then you were "wasting" the good preamps in the V3 and adding more noise than necessary with the R09's lesser gain stage.

At the same time, if you set the R09's levels "too low", at worst you might be brickwalling the R09 (although it could take a pretty hot signal - we're talking hypotheticals here) and even if you weren't brickwalling it, hypothetically you might be activating an un-necessary additional attenuation stage that might itself introduce noise, and meant you were adding more gain (and thus potentially more noise) than you really needed to be adding with the V3.

So "in theory", it made sense to look for some magical "unity gain (sic - meaning this isn't really unity gain either)" level where the R09 would be passing on the V3's signal to its A/D converter with as little additional mucking about as possible.  But finding the level where the R09's line output voltage matched the input voltage wasn't necessarily that magical level - for one thing what really matters is the internal voltage reaching the recorder's internal A/D relative to its nominal level -- the output levels for the recorder are irrelevant.  But also as mshilarious pointed out you often have sequences of attenuators and gain stages, only some of which can be bypassed - so given an un-bypassable stage, "correcting for it" to get back to unity is actually resulting in more mucking about with the signal than the minimum amount of mucking possible with that recorder.
« Last Edit: December 25, 2011, 11:53:08 PM by Will_S »

Offline DSatz

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Re: The myth of unity gain
« Reply #10 on: December 26, 2011, 01:01:55 AM »
If a given setting of the record gain control results in the recorder having voltage in = voltage out, that's unity gain, and I'm not arguing with that use of the term.

I'm only saying that the "lowest safe setting" of the record level control on a given recorder isn't necessarily the same as its unity gain setting. There's simply no inherent reason why the two should coincide, other than that "it would be nice." If you know the unity gain setting for your recorder, but you treat that bit of information as if it told you the lowest safe setting, then with some recorders, you could still get distorted recordings due to input overload even when 0 dB isn't being reached. Or conversely, you could be missing the chance to set levels that would give your recordings a better signal-to-noise ratio.

So we need to find out the lowest safe setting for each recorder (which is easy to do) and pass that information around, instead of finding the unity gain setting and pretending that it tells us anything about the recorder's safe range of settings.

Is that a little clearer, I hope?

--best regards
« Last Edit: December 26, 2011, 01:05:46 AM by DSatz »
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Re: The myth of unity gain
« Reply #11 on: December 26, 2011, 01:08:47 AM »
Yeah, thats a lil better!
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Offline John Willett

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Re: The myth of unity gain
« Reply #12 on: December 26, 2011, 08:07:34 AM »
Hi. May I post a Christmas rant that I hope will help someone in the long run?

I just read a discussion thread in which someone advised a new user to keep the record level control on a certain recorder set higher than about 4 or 5, since that was that recorder's "unity gain" point, and lower settings might lead to overload distortion even if the meters were below 0 dB and the red lights weren't flashing.

Many people here give advice like that. The advice could well be OK in many cases. But in other cases it could be off by enough to make someone end up with an overloaded recording despite their best efforts to avoid it. To understand why I say that, please follow me through the following set of reasons which I've compulsively organized into three blocks of three statements each:
  • Nearly all recorders have active first-stage amplifiers at their inputs rather than passive, variable resistors.
  • Every active circuit has an input overload limit--a signal voltage high enough to force the circuit out of its linear range.
  • Thus there is nearly always some input voltage high enough that if it occurred, it would overload the recorder's input stage and cause distortion.
  • Recording level controls generally affect incoming signals only after those signals have passed through the input stage.
  • (Record level controls are misnamed; they really only control the voltage gain at one point in the recorder's signal path. Recording level is a function of the input voltage, the voltage gain set by the control, and the fixed gain in the rest of the recording circuitry.)
  • If distortion occurs in the input stage, the action of the recording level control will be too late to stop it. In that case your "record level" setting will only determine the level at which you record the distortion. You can set it so that the meters only go to -20 and the overload LEDs never come on; you'll still have distortion due to input overload.
  • If there is a certain voltage above which input stage overload will occur, then there must also be a setting of the record level control at which a signal having that voltage would reach exactly 0 dB (full scale) on the recorder's meters.
  • If you find yourself wanting to set the record level control any lower than that setting in order to avoid reaching 0 dB on the meters, you probably have an input overload problem that needs a separate solution.
  • Thus it's well worth knowing what that control setting is for any recorder that you're using.
However (and this is my point), that setting of the record level control has nothing directly to do with the so-called "unity gain" setting of the device. The two things are independent and can very well differ from one another. I don't have any specific examples but in a given instance, setting a recorder's level control to its "unity gain" setting could still allow input overload to occur before 0 dB (full scale) is reached and before the "overload" indicators come on. Thus if you tell someone that the "unity gain" setting is the lowest safe setting, you may be giving them a false sense of safety.

The only reliable way to find the lowest safe setting is first to find the actual input overload point with a signal generator--then feed that level of signal (or just slightly below it) in to the recorder and observe the level setting at which 0 dB is reached on the meter. That's the safe setting limit for the control on that recorder. The voltage that happens to appear at the line level outputs of the recorder at that point is irrelevant; it may be similar to, or it may be higher than or lower than the voltage being fed in.

I urge everyone who refers to "unity gain" in this context to stop doing so, and replace the concept in your thinking with what really goes on.

--best regards

Well said DSatz - a very good and well argued post - I totally agree.

Many video cameras suffer from this problem - the level control is after the first amplification stage and it was very easy to distort this first stage even though the meters were showing well safe.  This is why Sennheiser did a special padded-down version of the K6 for video cameras to prevent overload of the first stage.
 

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Re: The myth of unity gain
« Reply #13 on: December 26, 2011, 08:40:40 AM »
If a given setting of the record gain control results in the recorder having voltage in = voltage out, that's unity gain, and I'm not arguing with that use of the term.

I'm only saying that the "lowest safe setting" of the record level control on a given recorder isn't necessarily the same as its unity gain setting. There's simply no inherent reason why the two should coincide, other than that "it would be nice." If you know the unity gain setting for your recorder, but you treat that bit of information as if it told you the lowest safe setting, then with some recorders, you could still get distorted recordings due to input overload even when 0 dB isn't being reached. Or conversely, you could be missing the chance to set levels that would give your recordings a better signal-to-noise ratio.

So we need to find out the lowest safe setting for each recorder (which is easy to do) and pass that information around, instead of finding the unity gain setting and pretending that it tells us anything about the recorder's safe range of settings.

Is that a little clearer, I hope?

--best regards

When ever I use the term, I mean exactly what you state in your first sentence. But - I think I(we) use the term loosely - and without regard to any true measurements.
Also - note - when we use the term "unity", we are almost always referring to a preamp feeding a line level to a recorder.
I think what we're saying is that a "theoretical" unity is good starting point - and NOT a lowest safe setting.  If anything, I think of unity as the "highest safe setting"

I used to tell people just to record a line level from CD player - and get a ball park idea where "unity" was and use that for a starting point.
Your first post sounds more like a desciption of "brickwalling." (a term I think you've claimed we made up or doesnt really exist ;))

I used to have device by Midiman called the Flying Calf A/D - it had no level controls - just meters and inputs. You drove it from your mixer...I think thats the model we are going for here.

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Re: The myth of unity gain
« Reply #14 on: December 26, 2011, 10:50:59 AM »
Thanks guys for the follow-up posts that help clarify the issue.  Much appreciated.  After getting a better understanding of the differences between the terms 'unity gain' and 'recommended input setting', for accuracy I'll carry the recommendations forward in my net conversations.

I'm still a little bit confused though.  In the follow-up discussion, the focus was on ensuring the proper use of the term 'lowest recommended input setting'.  In the context of the discussions in which the unity gain term was improperly applied, the goal is to make sure that the setting on your recorder is BELOW a specific point to make sure that the recorder isn't either overloading or mucking up the more desirable external pre-amp input gain, wouldn't the proper use of the term be to specify the 'highest recommended input setting'?
« Last Edit: December 26, 2011, 11:09:30 AM by tonedeaf »

Offline Walstib62

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Re: The myth of unity gain
« Reply #15 on: December 26, 2011, 11:20:53 AM »
DSatz,

Thanks for the post. It is sometimes diificult to find a way to explain complex technical terms in "layman's" terms. I think the whole point of the OP was a caution that using the "unity gain" setting of a given recorder does not prevent, in all cases, input stage overload, or clipping. (Often called brickwalling here)

First of all, the term unity gain, as DSatz mentioned, means voltage in=voltage out for a given amplifier. Normally, this term is applied to a SINGLE amplifier stage. The term has been adopted here to mean votage in to recorder=voltage out of recorder. The recorder can (will) have numerous amplifier stages in use. You can still input too high of a voltage to the input stage of a recorder and have a reasonable reading on the record level meters because they are measuring an amplifier stage which is not the input stage. (e.g A/D stage)
Here's a good real world exampe:
You are using mics (brand doesn't matter) into a V3. the line out of the V3 is then connected to the XLR input of a PMD 661. Instead of selecting "line in" the "mic in" is selected and input attenuation is applied, say -12 dB. You set the recorder at 4. You then adjust the levels on the V3 to just below 0dB on the recorder's meter. You have more than likely just overloaded the input stage of the recorder with never seeing a meter indication over 0. This is because the input stage clipped, and the record level control set that clipped signal to a level just below 0, and the meter was happy.

It would be ideal to have 2 sets of meters. One to monitor the input stage, and another to monitor the D/A stage. Then you would know you have the correct settings where they are most critical. You can actually do this if you record to a computer, because most software will allow selection of input signal monitoring as well as output levels. Plus, you can see the waveform as it's recording. I once saw a clipped soundboard waveform that was recording at -10 dB . I knew I had to attenuate the input signal to get it under control. Otherwise, I would not have known until playback. (Music was too loud to monitor correctly with headphones, at least with MY ears)   
 

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Re: The myth of unity gain
« Reply #16 on: December 26, 2011, 11:48:14 AM »
Good thread!

I think an important issue here is simply one of terminology.

We need a good clear term that everyone can use to describe "the lowest safe setting of the record level control without fear of overload".  That phrase just doesn't roll off the tounge and is too much to type, and the term 'unity gain' has become miss-appropriated around here.  We need a good short term for it.
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Offline Walstib62

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Re: The myth of unity gain
« Reply #17 on: December 26, 2011, 12:42:13 PM »
Good thread!

I think an important issue here is simply one of terminology.

We need a good clear term that everyone can use to describe "the lowest safe setting of the record level control without fear of overload".  That phrase just doesn't roll off the tounge and is too much to type, and the term 'unity gain' has become miss-appropriated around here.  We need a good short term for it.

As someone already said, it might be better to think of it as the "highest safe setting." A lot of folks are using external preamps to "condition" the signal so that the recorder does not add unwanted noise. It seems in some cases that these ext. pre's might be driven a little too high in the hopes that a hotter preamp signal is better. In most cases, with even a resonalbly decent recorder, this is just not the case. Usually the weak link in the noise chain is the mics anyway. Driving even a stellar preamp does not reduce the amount of noise in the signal. It just amplifies that noise cleanly.
While we're there, another often used term is "headroom" This  means how much additional, useable function is available in a given audio circuit,  in terms of gain. For example, the headroom for a preamp is how much additional gain is available for a given signal before clipping occurs. So, if your preamp has 70 dB of clean gain, and the signal going into that preamp is 40 dB, then you have 30 dB of headroom. I have heard some folks say that they listen to a recording and it has a lot of great "headroom" on playback. Or that a given preamp has more headorom than another based on how it sounds on playback. What does that mean???? It is not something that can be heard, it is something that can be measured.

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Re: The myth of unity gain
« Reply #18 on: December 26, 2011, 12:54:56 PM »
Maybe not, because below that point you might just have 0dB gain in the input stage and attenuation after the input stage which doesn't help input stage clipping and may or may not help with ADC clipping.  If in testing you discover that there is some point below which the input is still clipped and just being reduced below 0dBFS (such that you have a signal that is clipped with its flat-top peaks at say -12dBFS), then there is no reason to use those settings--they are giving you a false sense of security.

Jon, please forgive me...I just don't understand your response or the point about false sense of security. 

In the context of most conversations where the 'unity gain' term was used, it was in reference to a setting on a handheld...R-09, R-09HR, M10, PMD-620, and a maybe a couple others in which people (mostly noobs) were trying to gauge where they should set their recorders.  As you know, handheld recorders have one setting only...a control with a correponding numeric range that goes from 0 to X. 

Is it OK or is it not OK to state that the 'highest recommended setting' (or whatever term will be used in place of the formerly incorrecly applied 'unity gain' term) on the numeric scale of the recorder should be Y to avoid distortion, with Y being a value that has been determined to be roughly where a noob should set his recorder so that there is a nearly 100% chance that the recorder won't contribute any distortion? 

Isn't the false sense of security you're talking about removed, for example, by setting an m10 at 3 instead of 4 (because maybe 4 was felt to be the optimal setting because that's where someone incorrectly thought that voltage in = voltage out).
« Last Edit: December 26, 2011, 01:11:20 PM by tonedeaf »

Offline Walstib62

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Re: The myth of unity gain
« Reply #19 on: December 26, 2011, 01:08:20 PM »
Maybe not, because below that point you might just have 0dB gain in the input stage and attenuation after the input stage which doesn't help input stage clipping and may or may not help with ADC clipping.  If in testing you discover that there is some point below which the input is still clipped and just being reduced below 0dBFS (such that you have a signal that is clipped with its flat-top peaks at say -12dBFS), then there is no reason to use those settings--they are giving you a false sense of security.

Jon, please forgive me...I just don't understand your response or the point about false sense of security. 

In the context of most conversations where the 'unity gain' term was used, it was in reference to a setting on a handheld...R-09, R-09HR, M10, PMD-620, and a maybe a couple others in which people (mostly noobs) were trying to gauge where they should set their recorders.  As you know, handheld recorders have one setting only...a control with a correponding numeric range that goes from 0 to X. 

Is it OK or is it not OK not to state that the 'highest recommended setting' (or whatever term will be used in place of the formerly incorrecly applied 'unity gain' term) on the numeric scale of the recorder should be Y to avoid distortion, with Y being a value that has been determined to be roughly where a noob should set his recorder so that there is a nearly 100% chance that the recorder won't contribute any distortion? 

Isn't the false sense of security you're talking about removed, for example, by setting an m10 at 3 instead of 4 (because maybe 4 was felt to be the optimal setting because that's where someone incorrectly thought that voltage in = voltage out).
Gnerally speaking, yes, but not in all cases. For example, say you have a screaming hot input to the deck. You could set the record level at at 1 to just get below 0 dB, with no clip indicators flashing. There is almost a 100% chance that the signal is clipped all to hell at the input stage. The real take away here is that if you are pushing the recorder input down and pushing the external preamp signal up then you are increasing the chances of overloading the recorder's input.
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« Last Edit: December 26, 2011, 01:11:38 PM by Walstib62 »

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Re: The myth of unity gain
« Reply #20 on: December 26, 2011, 01:11:43 PM »
Next time I'm making a bootleg, I'll make sue the knob thingy is set below unity gain.

;) vs.

Next time I record a show, I'll set my input levels lower to avoid clipping. If that doesn't work, I'll attenuate the input to avoid overloading the input stage.

While inaccurate language works, accurate terminology increases the chance of accurate communication, and makes learning easier
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Re: The myth of unity gain
« Reply #21 on: December 26, 2011, 01:26:47 PM »
While inaccurate language works, accurate terminology increases the chance of accurate communication, and makes learning easier

I don't disagree with the first portion of your statement, but the part in bold is your humble opinion.  Analogies and non-techical language are very helpful and needed in many situations to help communicate with people that don't have a similar background or technical understanding.

While I'm finally getting an understanding of what several people are trying to communicate, I personally have found nothing 'easy' about the accurate terminology that's been used in this thread.

Just sayin...
« Last Edit: December 26, 2011, 01:31:17 PM by tonedeaf »

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Re: The myth of unity gain
« Reply #22 on: December 26, 2011, 01:38:10 PM »

Is it OK or is it not OK to state that the 'highest recommended setting' (or whatever term will be used in place of the formerly incorrecly applied 'unity gain' term) on the numeric scale of the recorder should be Y to avoid distortion, with Y being a value that has been determined to be roughly where a noob should set his recorder so that there is a nearly 100% chance that the recorder won't contribute any distortion? 


I think you're still getting it backward, as are a few other folks in this thread.  From the point of avoiding distortion (at least, the kind that wouldn't be given away by the level meters indicating clipping), there is no "highest safe" setting.  There may be a higher than optimal from an added noise standpoint, but the problem is when folks turn the recording level down to accommodate an overly hot input.  There are many recorders that allow you to reduce the recording level so that a too-hot input signal (i.e., one the recording deck simply cannot accommodate - one that needs to be attenuated BEFORE it even hits the recorders input) gives levels on the dB meters that look ok, but in fact is simply clipping below full scale because it is overloading something in the deck upstream of the level meters, and that overdriven stage is simply passing on a clipped wave form that later stages are boosting or attenuating, but cannot unclip.

So what you need to look for is the LOWEST setting.  If you need to set your recorder BELOW that to avoid clipping on the meters, your input signal is too hot, and turning down your recording levels just gives you a clipped waveform that has been shrunk down.
« Last Edit: December 26, 2011, 07:06:28 PM by Will_S »

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Re: The myth of unity gain
« Reply #23 on: December 26, 2011, 02:19:59 PM »
Jon,

Thanks for the very detailed post. I was just trying to make a point of how the term is misunderstood and putting it in very (over) simplified terms. I'm sure your values are correct. I was just throwing numbers out there for example, to sort of illustrate the concept. I should not have thrown random numbers out without checking the accurcy. I don't have that stuff on my brain anymore. I have to look it up. Anyway thanks for the correction.

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Re: The myth of unity gain
« Reply #24 on: December 27, 2011, 12:19:16 PM »
Lots of good info in this thread, thanks to DSatz for a well-reasoned and informative post to get it started.

I would like to amplify on something Will brought up:  DSatz has explained how "unity gain" is not the same thing as what is being called minimum level setting (or more clearly to me, maximum input level), but Will also noted that many here are assuming unity gain is great because it means like dood, you just have a straight wire then, man.

That is also a huge myth, perhaps not as dangerous as the maximum input level myth that DSatz brings up, but I'd guess more widespread here.  The idea is that if you can find unity gain on your recorder, then you're just recording exactly what you preamp put out, and you haven't changed the signal at all -- no different than having just a straight wire.

Except that it isn't -- you don't have effectively a straight wire just because you are at unity gain.  The recorder's signal path doesn't change at all, so if you're going through a series of passive attenuators and active gain stages, you're still going through all those same signal path elements regardless of where you have your gain set.  Whether or not it will sound better being at unity gain probably depends on a lot of design factors and parts used, but unity gain is not some magical place where you have effectively replaced the entire signal path with a straight wire.
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Re: The myth of unity gain
« Reply #25 on: December 27, 2011, 12:34:12 PM »
Also, particularly to Steve and perhaps others: I think you've got some confusion on the issue that DSatz and Will have been talking about, since like Will said, it seems you have it backwards.

You've got examples saying that if you have distortion at level setting 4, then the solution is to keep no higher than setting 3.  That isn't the issue here, and it won't solve the problem, it will only mask it since you won't be seeing digital clipping by trying to go above 0dbFS.

You could have 3 kinds of distortion:  signal input is too high for the max input of the recorder, output signal from the active gain stage is higher than the gain stage can provide (output distortion from the analog gain stage), or distortion from going above 0dbFS when converting to a digital signal.

In a well-designed recorder, you wouldn't ever get the second kind of distortion:  it would not be possible to get into the output distortion realm without already going over 0dbFS after your A>D conversion stage.  This kind of distortion though would be an area where you are getting distortion at level setting 4, but it is resolved if you dial it back to level setting 3.  So that would be a case of needing a max level setting, but again this shouldn't happen if the recorder is designed well.

The third type of distortion is one we all are familiar with and try to avoid:  don't go into the realm of digital clipping by trying to exceed 0dbFS.

The discussion mainly in this thread is about input level distortion:  you are feeding a signal that is too hot for the recorder to handle without distortion.  And really it isn't so much about the minimum gain setting, in the sense that you can avoid this distortion by changing your gain setting.  It is that if you need to go below a certain gain setting to avoid going over 0dbFS, then you know you are going to have input distortion.  Thus, it isn't really a minimum gain setting that is the issue, it is that there is a maximum input level the recorder can take.  The minimum input level setting is just an indication that you will be exceeding that maximum input level.

The gain setting you use at that point will not solve your problem, it will only indicate that you have a problem.  The only solution as Will notes is to use an external attenuator to bring that signal down before it gets to the inputs of your recorder.

Hopefully that clears it up a bit more.
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Re: The myth of unity gain
« Reply #26 on: December 27, 2011, 01:03:09 PM »
Lots of good info in this thread, thanks to DSatz for a well-reasoned and informative post to get it started.

I would like to amplify on something Will brought up:  DSatz has explained how "unity gain" is not the same thing as what is being called minimum level setting (or more clearly to me, maximum input level), but Will also noted that many here are assuming unity gain is great because it means like dood, you just have a straight wire then, man.

That is also a huge myth, perhaps not as dangerous as the maximum input level myth that DSatz brings up, but I'd guess more widespread here.  The idea is that if you can find unity gain on your recorder, then you're just recording exactly what you preamp put out, and you haven't changed the signal at all -- no different than having just a straight wire.

Except that it isn't -- you don't have effectively a straight wire just because you are at unity gain.  The recorder's signal path doesn't change at all, so if you're going through a series of passive attenuators and active gain stages, you're still going through all those same signal path elements regardless of where you have your gain set.  Whether or not it will sound better being at unity gain probably depends on a lot of design factors and parts used, but unity gain is not some magical place where you have effectively replaced the entire signal path with a straight wire.

Great summary of the myth...I can see where there have been some wrong conclusions along the way.

For me - some of my misconceptions come from using standalone A/D converters with no knobs...

Im can remember the term being used here in the jb3 heyday - as people were trying to interface various rigs with it.

The whole "lowest safe setting" and "straightwire" business seem to be subsequent conclusions.

Im as guilty as anyone in using the term - but I surely never meant to imply any level of "safety" - just a good, relatively safe, starting point for someone trying to get a feel for new gear.

I've read all the replies in this thread - and still - I dont see why it isnt a good piece of general advice for a guy who just got some new gear and is trying to put it through the paces?

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Re: The myth of unity gain
« Reply #27 on: December 27, 2011, 01:03:49 PM »
I've often wondered why manufacturers of inexpensive recorders don't set the input-stage gain controls up as described in this thread.  Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?  Why don't manufacturers simply use that point as the starting point of the input gain adjustment so that the input stage will not clip before the ADC?

The only reason I can think of for allowing the input setting range to go lower would be to allow the user to fade-in or fade-out using the input gain control.  Do users actually do that with these recorders, even in the 'larger real world market' outside of TS?
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Re: The myth of unity gain
« Reply #28 on: December 27, 2011, 01:16:56 PM »
I've often wondered why manufacturers of inexpensive recorders don't set the input-stage gain controls up as described in this thread.  Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?  Why don't manufacturers simply use that point as the starting point of the input gain adjustment so that the input stage will not clip before the ADC?

The only reason I can think of for allowing the input setting range to go lower would be to allow the user to fade-in or fade-out using the input gain control.  Do users actually do that with these recorders, even in the 'larger real world market' outside of TS?

"Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?"

Ok - now im confused again - that sounds totally counter-intuitive...lowest gain...before overloading - how does low input gain cause overloading?

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Re: The myth of unity gain
« Reply #29 on: December 27, 2011, 01:18:13 PM »

I've read all the replies in this thread - and still - I dont see why it isnt a good piece of general advice for a guy who just got some new gear and is trying to put it through the paces?

I don't think it is necessarily a bad thing or bad advice.  And it does seem logical to assume that a recorder will behave "normally" (eg, not distort) if you have levels set somewhere near unity gain.

But it is important to understand what you're getting and not getting.  Not getting as DSatz points out some guarantee that you won't have distortion, for example.  Also, all the talk about unity gain does then seem to lead some to freak out that they have their recorder set at 7 when unity is 4, especially when there is every likelihood (or at least possibility) that it will sound exactly the same when set at 7 (and the external preamp adjusted accordingly), than it would when set to 4 (with a slightly different gain setting on the external preamp).
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Re: The myth of unity gain
« Reply #30 on: December 27, 2011, 01:21:12 PM »
I've often wondered why manufacturers of inexpensive recorders don't set the input-stage gain controls up as described in this thread.  Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?  Why don't manufacturers simply use that point as the starting point of the input gain adjustment so that the input stage will not clip before the ADC?

The only reason I can think of for allowing the input setting range to go lower would be to allow the user to fade-in or fade-out using the input gain control.  Do users actually do that with these recorders, even in the 'larger real world market' outside of TS?


I've wondered the same thing.  The fading in/out might be a part of it, or maybe folks want their peaks below full scale to leave headroom for later mixing or other manipulations (yes I realize they could just lower the volume in post - and folks wouldn't need nearly as much headroom for mixing as some level adjustments allow). I also wonder if in some cases the full numeric range may be usable under some settings but not others (e.g. if on one setting of the mic sensitivity switch but not another), but that doesn't seem to the case with the gear I've used.



"Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?"

Ok - now im confused again - that sounds totally counter-intuitive...lowest gain...before overloading - how does low input gain cause overloading?

runonce:  The low input setting doesn't CAUSE overloading, it MASKS it on a too-hot signal that has already been clipped, but a reduced recording level setting then sends a shrunken down but still clipped waveform to the later parts of the recording chain, including the level meters which will show levels well shy of full scale even though the waveform has been clipped.

So a low recording level setting doesn't cause distortion.  But if your input signal is so hot that you need to go below a certain recording level for it to LOOK below full scale on the level meters, it's a way of knowing that your input signal is simply too hot for that particular recorder to deal with.

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Re: The myth of unity gain
« Reply #31 on: December 27, 2011, 01:22:16 PM »

"Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?"

Ok - now im confused again - that sounds totally counter-intuitive...lowest gain...before overloading - how does low input gain cause overloading?

Yes, unless I'm confused, this is where I say it would be more useful to discuss maximum input level rather than lowest gain setting.

Saying "Why should the user have to use test tones to find the maximum input level before overloading the input-stage?" makes total sense to me, and doesn't cause me any confusion.

Personally, I don't want to mess with signal generators and o-scopes to determine when distortion is setting in.  I just wish all manufacturers would provide easy-to-find and accurate specs on things like maximum input level for incoming analog inputs.  I can figure it out from there.
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Re: The myth of unity gain
« Reply #32 on: December 27, 2011, 01:28:15 PM »

"Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?"

Ok - now im confused again - that sounds totally counter-intuitive...lowest gain...before overloading - how does low input gain cause overloading?

Yes, unless I'm confused, this is where I say it would be more useful to discuss maximum input level rather than lowest gain setting.

Saying "Why should the user have to use test tones to find the maximum input level before overloading the input-stage?" makes total sense to me, and doesn't cause me any confusion.

Personally, I don't want to mess with signal generators and o-scopes to determine when distortion is setting in.  I just wish all manufacturers would provide easy-to-find and accurate specs on things like maximum input level for incoming analog inputs.  I can figure it out from there.

To some extent I agree, but if you want to give a new taper guidance on how to avoid overload distortion, do you want to get into dBV vs dBu, nominal versus peak levels, and all that jazz?

Plus, for something like a soundbard patch:  even if I know what the spec'd maximum output level of a particular mixer is, I've found that in practice the actual output signal won't be nearly that hot for the shows I record.  So it's handy to know, without bringing along measurement gear to figure out exactly how hot the board is running that night, that if I need to turn my recording levels below XX I better stick my attenuator cable in there but otherwise I have one less connection and piece of gear to fuss with.

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Re: The myth of unity gain
« Reply #33 on: December 27, 2011, 01:33:38 PM »
I've often wondered why manufacturers of inexpensive recorders don't set the input-stage gain controls up as described in this thread.  Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?  Why don't manufacturers simply use that point as the starting point of the input gain adjustment so that the input stage will not clip before the ADC?

The only reason I can think of for allowing the input setting range to go lower would be to allow the user to fade-in or fade-out using the input gain control.  Do users actually do that with these recorders, even in the 'larger real world market' outside of TS?


I've wondered the same thing.  The fading in/out might be a part of it, or maybe folks want their peaks below full scale to leave headroom for later mixing or other manipulations (yes I realize they could just lower the volume in post - and folks wouldn't need nearly as much headroom for mixing as some level adjustments allow). I also wonder if in some cases the full numeric range may be usable under some settings but not others (e.g. if on one setting of the mic sensitivity switch but not another), but that doesn't seem to the case with the gear I've used.



"Why should the user have to use test tones to find the lowest input gain setting before overloading the input-stage?"

Ok - now im confused again - that sounds totally counter-intuitive...lowest gain...before overloading - how does low input gain cause overloading?

runonce:  The low input setting doesn't CAUSE overloading, it MASKS it on a too-hot signal that has already been clipped, but a reduced recording level setting then sends a shrunken down but still clipped waveform to the later parts of the recording chain, including the level meters which will show levels well shy of full scale even though the waveform has been clipped.

So a low recording level setting doesn't cause distortion.  But if your input signal is so hot that you need to go below a certain recording level for it to LOOK below full scale on the level meters, it's a way of knowing that your input signal is simply too hot for that particular recorder to deal with.

Understood - I think thats what we call the classic brickwall. Im sure we've all experienced a show where the meters just didnt look quite right. Predictably - the waveform will look flat, but still show plenty of headroom.

We're usually talking about this relative to the mic>preamp connection - but now "unity myth" takes it to the preamp>recorder context.

At that point it gets harder to talk about because I think everyone is thinking of their own gear... :P

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Re: The myth of unity gain
« Reply #34 on: December 27, 2011, 01:42:24 PM »
Will_S:  agreed, it's just if you dumb things down too much, people don't learn the basics, and we have all these myths and misconceptions.

I think it is important for tapers to learn the basics, and in this case that is that you can send too hot of an analog signal into your preamp or recorder, and cause distortion.  Then after that, we can discuss the shortcut of determining whether this input-overload situation is occurring is when you have to turn your recorder down below level setting 2 or whatever it is.  The problem seems to be that if we skip to the shortcut on how to determine if there is a problem, there ends up being a lot of people who don't understand what the basic problem is at hand.

Agreed though: it is very useful to know for the various recorders where that minimum level setting that indicates input overload is -- very helpful bit of field advice to have at your disposal.
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Re: The myth of unity gain
« Reply #35 on: December 27, 2011, 03:02:29 PM »
Dang it.  I'm really dense today.  LOL. 

Will, Todd, Jon, et al.

I thought I always understood how input signal could be peaking without that showing on your recorder levels. 

However, it was always my understanding that the electronics of the recorder itself could cause us to mess up our recording because it can add too much gain and that was a concern AS WELL because it could also mess up a clean input signal.  This context was discussed without any regard to whether the input is clean or distorted.  So, just to help those of us that are confused/stuck, please answer the following question...

If one knows beyond any doubt that their input signal is clean, can they mess up their recording by setting the levels on their recorder too high, even if the meter on the recorder isn't peaking? 

(Please, if possible to help avoid further confusion, I'm just looking for a basic answer of yes or no with some really noob-ish language about why the answer is yes or why it's no.  All the technical discussion just confuses this basic question for me...and I think others.)

Thanks.
« Last Edit: December 27, 2011, 03:17:30 PM by tonedeaf »

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Re: The myth of unity gain
« Reply #36 on: December 27, 2011, 03:05:39 PM »
Yes, unless I'm confused, this is where I say it would be more useful to discuss maximum input level rather than lowest gain setting.

Saying "Why should the user have to use test tones to find the maximum input level before overloading the input-stage?" makes total sense to me, and doesn't cause me any confusion.
^^^
This makes sense to me and does seem less confusing.  I'll try and adopt the phrase maximum input level before overloading the input when I describe this.  The next step will then be to explain the difference between that and the input gain setting.

Quote
Personally, I don't want to mess with signal generators and o-scopes to determine when distortion is setting in.  I just wish all manufacturers would provide easy-to-find and accurate specs on things like maximum input level for incoming analog inputs.  I can figure it out from there.

Yes!  That shouldn't be too much to ask, simply providing information on the recorders as they now exist.

However, I really don't understand why manufacturers don't set up the input gain setting range as I've described.  It would make problem free recording much simplier all users of the device, especially less techical users that would be complely lost in following this discussion, much less care about it.. except for being confused and disappointed when they get brick-walled recordings even though they've adjusted the recording level of the recorder so that everything looks right on the meters.
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Re: The myth of unity gain
« Reply #37 on: December 27, 2011, 03:16:46 PM »
If one knows beyond any doubt that their input signal is clean, can they mess up their recording by setting the levels on their recorder too high, even if the meter on the recorder isn't peaking? 

Not really.  I'm temped to say no outright, but yes if you consider too much hiss as messing up the recording. If the preamp stage built into the recorder is not very quiet, setting the input gain level too high will introduce that excess noise (preamp hiss).  But that's less of a catastrophic problem than clipping the input stage (the opposite scenario we've been considering here), plus the level meters should accurately reflect the recording level in that case and won't lie, so there is far less possibility for confusion. 

It would not be an issue at all if only using the internal preamp.  Using an external preamp that has adjustable gain, you can trade off how much gain you add with that verses how much gain you add with the internal circuit.  If you add only a minimal amount with the external preamp and a lot of gain with the noisier internal circuit, you will introduce more noise as hiss, messing up your recording that way.  But that is pretty obvious to most users around here and counter to how they typically operate things, plus as mentioned, even if someone was to set their gains that way, the recorder's meters should still accurately indicate any overload peaks.
« Last Edit: December 27, 2011, 03:30:00 PM by Gutbucket »
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Re: The myth of unity gain
« Reply #38 on: December 27, 2011, 03:20:47 PM »

If one knows beyond any doubt that their input signal is clean, can they mess up their recording by setting the levels on their recorder too high, even if the meter on the recorder isn't peaking? 


I'd say, practically speaking, no.

The clean input signal (if too hot) can be messed up by the recorder (since it cannot accept that high of an input signal), but setting levels would have nothing to do with this:  it will be screwed up, but not because of what happens with setting levels.

Setting levels could screw up a clean signal even without the recorder peaking (ie, trying to go above 0dbFS) if a recorder was designed very poorly (this is the second type of distortion I discussed in my post above). 

But that is a foolish way of designing a recorder -- if there is an upper limit on how hot of an output your active gain stage can accomplish, since that active gain stage comes right before the A/D converter and is all inside the box of the recorder, it would be stupid to design your recorder such that that max output level can only achieve a digital level of say -4dbFS -- then you're just asking someone to overload the output of the gain stage by trying to get to -1dbFS.  Instead, you would design the recorder such that the A/D stage would output 0dbFS before you got to that max output level.  Thus, in practical terms, you would not have anyway of distorting your recording by setting the input level above a certain point, with the exception of going above (trying to go above) 0dbFS -- that is besides peaking your recording as you call it.

This is why I say the issue isn't learning where the max input setting is -- there really is no such thing, or perhaps rather, avoiding what that level setting is simply means you should not go above 0dbFS or have clipping -- and usually there already is a clip meter/LED on recorders to show you this, so it would be obvious.
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Re: The myth of unity gain
« Reply #39 on: December 27, 2011, 03:26:26 PM »
If one knows beyond any doubt that their input signal is clean, can they mess up their recording by setting the levels on their recorder too high, even if the meter on the recorder isn't peaking? 

Not really.  I'm temped to say no outright, but yes if you consider too much hiss as messing up the recording. If the preamp stage built into the recorder is not very quiet, setting the input gain level too high will introduce that excess noise (preamp hiss).  But that's less of a catastrophic problem than clipping the input stage (the opposite scenario we've been considering here), plus the level meters should accurately reflect the recording level in that case and won't lie, so there is far less possibility for confusion. 

It would not be an issue at all if only using the internal preamp.  Using an external preamp, you can trade off gain with that verses gain with the internal circuit, so if you added a minimal amount of gain wth the external preamp and alot of gain with the noisier internal circuit, you would get more noise as hiss, messing up your recording that way.  But that is more obvious to most users, and as mentioned, the recorders meters should accurately indicate any overload peaks.

Thank you.  That TOTALLY explains my confusion then because it was my apparently incorrect understanding that the recorder itself could add distorted gain...thus when discussing unity gain, my incorrect conclusion was that you'd never want to go over that in order to be safe against the potential for adding distortion from the recorder. 

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Re: The myth of unity gain
« Reply #40 on: December 27, 2011, 03:32:56 PM »

If one knows beyond any doubt that their input signal is clean, can they mess up their recording by setting the levels on their recorder too high, even if the meter on the recorder isn't peaking? 


I'd say, practically speaking, no.

The clean input signal (if too hot) can be messed up by the recorder (since it cannot accept that high of an input signal), but setting levels would have nothing to do with this:  it will be screwed up, but not because of what happens with setting levels.

Setting levels could screw up a clean signal even without the recorder peaking (ie, trying to go above 0dbFS) if a recorder was designed very poorly (this is the second type of distortion I discussed in my post above). 

But that is a foolish way of designing a recorder -- if there is an upper limit on how hot of an output your active gain stage can accomplish, since that active gain stage comes right before the A/D converter and is all inside the box of the recorder, it would be stupid to design your recorder such that that max output level can only achieve a digital level of say -4dbFS -- then you're just asking someone to overload the output of the gain stage by trying to get to -1dbFS.  Instead, you would design the recorder such that the A/D stage would output 0dbFS before you got to that max output level.  Thus, in practical terms, you would not have anyway of distorting your recording by setting the input level above a certain point, with the exception of going above (trying to go above) 0dbFS -- that is besides peaking your recording as you call it.

This is why I say the issue isn't learning where the max input setting is -- there really is no such thing, or perhaps rather, avoiding what that level setting is simply means you should not go above 0dbFS or have clipping -- and usually there already is a clip meter/LED on recorders to show you this, so it would be obvious.

Wow, now that I've got the concept through my crazy thick brain, I understand what you've saying Todd.  Scary.  ;)


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Re: The myth of unity gain
« Reply #41 on: December 27, 2011, 03:48:04 PM »
 :-*  Glad we've penetrated your cerebral cortex Steve.  With many of us having yesterday off as a holiday, it is effectively Monday today, so I wouldn't worry about your thick-headedness. :)

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Re: The myth of unity gain
« Reply #42 on: December 27, 2011, 04:47:08 PM »
People that say unity gain will avoid distortion dont understand like Dsatz said the overload is happening in the front end of the preamp before any attenuation. That's why on mic preamps on consoles at least good ones ;) there is always a pad control to pad the input down before any buffering of the signal has occurred. The problem is now most gain controls in small recorders are digital and thus will overload even when the control is below unity gain. Unity gain assumes that what comes in goes out. But when there is a buffer amp in the front end of a preamp its already set to unity gain or in some cases it might have a 10 or 20 db gain in the that section to help increase signal to noise ratio its in this section that overload will occur and with digital attenuation there is no real potentiometer clamping down on the signal just a ic encoder chip and vca chip. Unity gain is really a term that applies more to recording or live console gain structure than it does to portable recording devices. In the end you should just always aim for -10 or so on your meters and know what the overload limit is of your gear. It can be pretty hard to figure that out with some of the test gear people like me have at my disposal. Generally speaking you want to look for the max gain in at a percentage of THD% It should be ideally less than 1% Its a complicated topic that Dsatz very easily spelled out in plain English :) Like he always does. I wish I could convey my thoughts as easily as he does its truly a rare talent for technically minded people like us, I have never mastered it.
« Last Edit: December 27, 2011, 04:49:31 PM by Church-Audio »
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Re: The myth of unity gain
« Reply #43 on: December 27, 2011, 05:30:44 PM »
Steve, since it's effectively Monday and I'm only partially working ;) , I'll try and take this one step further to shine some light on another commonly used technical term, which has been used in this thread, and better describes the actual thing users are trying to optimize when misapplying the term 'unity gain'.  By that I mean determining the limits of a comfortable range of gain settings which provide a good signal-to-noise ratio.  A good signal-to-noise ratio simply means getting more of what we want (signal) and less of what we don't want (noise).  'Noise' in this sense is anything we don't want, and it refers in this case specifically to two forms of noise which show up at opposite extremes of that comfortable range of gain settings- Noise in the form of overload distortion or clipping from a signal which is too hot at one extreme and excess hiss from needing to use too much gain on a signal that is too weak at the other.

There is a range of possible gain settings which will provide a good signal-to-noise ratio, not just a single setting.  The important thing is to find the comfortable 'safe zone' of the gain settings which avoid the problematic extremes.  It's not a single setting but a range, with brick-walling or clipping at one end and excess noise at the other.


The way in which the term 'unity gain' has been misused around here implies a single specific input-gain setting, and so in addition to being the incorrect term for what people are actually trying to optimize, it also is misleading in implying that there is only a single 'optimal' setting.

At the risk of confusing things again, I'll point out that even that mis-implication is incorrect.  As established in this thread, 'unity gain' simply means that the input voltage equals the output voltage, which DSatz pointed out somewhere earlier. [edit- and as Chirs just pointed out as well with regards to gain through mixing consoles] Most small recorders have separate controls for both input gain and for output gain of the line-out or headphone jack.  You can set the input gain way low but compensate by setting the output gain high enough so that the device would still be at ‘unity gain’ as long as the input voltage = the output voltage.  You could also do the opposite and set the input gain too high and the output gain low enough to achieve 'unity gain'.  In either case your signal-to-noise ratio would not be a good as a more reasonable setting for both, and that’s what we’re really concerned about.

Notice that the above description on different settings that all achieve ‘unity gain’ says nothing about actually recording anything on the machine, only about a signal passing through it having the same voltage going out as it did on the way in.  That’s the only way ‘unity gain’ applies for end-users.  When we get more technical and talk about the different stages of circuitry inside the device and how they interact, we might apply the ‘unity gain’ terminology in describing the gain through those internal circuits, but that doesn’t usually apply to anything the end user can adjust on these small recorders. [edit- Chris's example of a mixing console is a good one, since in that case the user can adjust signal gain at various points along the signal path on the console.]
« Last Edit: December 27, 2011, 08:24:51 PM by Gutbucket »
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Re: The myth of unity gain
« Reply #44 on: December 28, 2011, 03:08:44 AM »
Isn't the M10 a lil different tho, since if its MIC-IN or LINE-IN can go as low as possible to avoid clipping and/or levels below 0db ??? I cant put into words what I'm really trying to say :P
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Re: The myth of unity gain
« Reply #45 on: December 28, 2011, 03:13:20 AM »
I actually understood SOME of that. I have been  recording digitally for around 15 years now, and I don't know SHIT about the technical jargon :P :) I just know how to use the gear to get the best recording possible :)
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Re: The myth of unity gain
« Reply #46 on: December 28, 2011, 07:44:44 AM »
Isn't the M10 a lil different tho, since if its MIC-IN or LINE-IN can go as low as possible to avoid clipping and/or levels below 0db ??? I cant put into words what I'm really trying to say :P

Don't even go there Bean unless you want to drive yourself crazy like I have the last couple days.  That's what I've been trying to sort out in this thread for myself, but also for others that are confused by this...because I know there's a ton of people that have had a ton of discussion about this for at least a couple of years now when the discussion was 'unity gain' on the R-09, R-09HR, M10, PMD-620 and a couple others that I'm not coming up with.  According to the answers I've gotten in this thread, the answer is 'no'.

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Re: The myth of unity gain
« Reply #47 on: December 28, 2011, 10:48:55 AM »
^^^ On the M10, if you need to go below one on the rec level dial to keep from going over on the meters, you might be distorting at the input.  At least, that's where guysonic put it (http://taperssection.com/index.php?topic=130924.msg1722942#msg1722942)...

In that post, he also responds to a request about the M10's unity gain setting.  In his response, he says that, at 6, the "output jack signal equaled the input giving unity 'system gain.'"  I thought the word choice was interesting in light of this thread!  He doesn't elaborate, but he is definitely suggesting that there's more to the "voltage in equals voltage out" point than meets the eye...On some recorders, you can even get a pretty good feel for what's being added/attenuated internally from the specs (the DR-07, for example).

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Re: The myth of unity gain
« Reply #48 on: December 28, 2011, 11:03:35 AM »

In the context of most conversations where the 'unity gain' term was used, it was in reference to a setting on a handheld...R-09, R-09HR, M10, PMD-620, and a maybe a couple others in which people (mostly noobs) were trying to gauge where they should set their recorders.  As you know, handheld recorders have one setting only...a control with a correponding numeric range that goes from 0 to X. 

Is it OK or is it not OK to state that the 'highest recommended setting' (or whatever term will be used in place of the formerly incorrecly applied 'unity gain' term) on the numeric scale of the recorder should be Y to avoid distortion, with Y being a value that has been determined to be roughly where a noob should set his recorder so that there is a nearly 100% chance that the recorder won't contribute any distortion? 

Isn't the false sense of security you're talking about removed, for example, by setting an m10 at 3 instead of 4 (because maybe 4 was felt to be the optimal setting because that's where someone incorrectly thought that voltage in = voltage out).

Without regard to the technical discussion happening in this thread or whether it is the minimum safe setting or the highest recommended setting, the previous discussions I've read on the R-09, R-09HR and M10 have been how to minimize the impact (either amplification or attenuation) of the recorder's preamp.  In doing so, it was a hope that the noisier (?) internal preamps of the recorder could be avoided and the external preamp utilized instead.  While this may not be unity gain, I don't think we should lose sight of the desire to find the most neutral input setting on the recorder.  That is what I wanted to know - the most neutral recommended input setting.

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Re: The myth of unity gain
« Reply #49 on: December 28, 2011, 11:32:57 AM »

In the context of most conversations where the 'unity gain' term was used, it was in reference to a setting on a handheld...R-09, R-09HR, M10, PMD-620, and a maybe a couple others in which people (mostly noobs) were trying to gauge where they should set their recorders.  As you know, handheld recorders have one setting only...a control with a correponding numeric range that goes from 0 to X. 

Is it OK or is it not OK to state that the 'highest recommended setting' (or whatever term will be used in place of the formerly incorrecly applied 'unity gain' term) on the numeric scale of the recorder should be Y to avoid distortion, with Y being a value that has been determined to be roughly where a noob should set his recorder so that there is a nearly 100% chance that the recorder won't contribute any distortion? 

Isn't the false sense of security you're talking about removed, for example, by setting an m10 at 3 instead of 4 (because maybe 4 was felt to be the optimal setting because that's where someone incorrectly thought that voltage in = voltage out).

Without regard to the technical discussion happening in this thread or whether it is the minimum safe setting or the highest recommended setting, the previous discussions I've read on the R-09, R-09HR and M10 have been how to minimize the impact (either amplification or attenuation) of the recorder's preamp.  In doing so, it was a hope that the noisier (?) internal preamps of the recorder could be avoided and the external preamp utilized instead.  While this may not be unity gain, I don't think we should lose sight of the desire to find the most neutral input setting on the recorder.  That is what I wanted to know - the most neutral recommended input setting.

Yeah, that's a good point and as has been pointed out, you start running into problems when you roll your recorder levels back too far in hopes of minimizing the noisier recorder gain and maximizing external preamp gain because you could be overloading the external preamp.  You wouldn't realize it because the levels on your recorder may only be peaking at -12db or something like that...e.g. the infamous brickwall situation. 

My entire misunderstanding earlier in this thread (and what I was having trouble getting a grip on) was that I thought 'unity gain' was also important from the recorder perspective in the other direction...that it's also possible to distort your recordings (without levels peaking on the meter) simply because you take your recorder too far over that 'unity gain' point, but Todd and Gut are saying that's not going to happen without the recorder showing levels peaking...which now that I understand the whole discussion better makes complete sense to me.

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Re: The myth of unity gain
« Reply #50 on: December 28, 2011, 11:39:45 AM »

In the context of most conversations where the 'unity gain' term was used, it was in reference to a setting on a handheld...R-09, R-09HR, M10, PMD-620, and a maybe a couple others in which people (mostly noobs) were trying to gauge where they should set their recorders.  As you know, handheld recorders have one setting only...a control with a correponding numeric range that goes from 0 to X. 

Is it OK or is it not OK to state that the 'highest recommended setting' (or whatever term will be used in place of the formerly incorrecly applied 'unity gain' term) on the numeric scale of the recorder should be Y to avoid distortion, with Y being a value that has been determined to be roughly where a noob should set his recorder so that there is a nearly 100% chance that the recorder won't contribute any distortion? 

Isn't the false sense of security you're talking about removed, for example, by setting an m10 at 3 instead of 4 (because maybe 4 was felt to be the optimal setting because that's where someone incorrectly thought that voltage in = voltage out).

Without regard to the technical discussion happening in this thread or whether it is the minimum safe setting or the highest recommended setting, the previous discussions I've read on the R-09, R-09HR and M10 have been how to minimize the impact (either amplification or attenuation) of the recorder's preamp.  In doing so, it was a hope that the noisier (?) internal preamps of the recorder could be avoided and the external preamp utilized instead.  While this may not be unity gain, I don't think we should lose sight of the desire to find the most neutral input setting on the recorder.  That is what I wanted to know - the most neutral recommended input setting.

Yeah, that's a good point and as has been pointed out, you start running into problems when you roll your recorder levels back too far in hopes of minimizing the noisier recorder gain and maximizing external preamp gain because you could be overloading the external preamp.  You wouldn't realize it because the levels on your recorder may only be peaking at -12db or something like that...e.g. the infamous brickwall situation. 

My entire misunderstanding earlier in this thread (and what I was having trouble getting a grip on) was that I thought 'unity gain' was also important from the recorder perspective in the other direction...that it's also possible to distort your recordings (without levels peaking on the meter) simply because you take your recorder too far over that 'unity gain' point, but Todd and Gut are saying that's not going to happen without the recorder showing levels peaking...which now that I understand the whole discussion better makes complete sense to me.

If your recorders gain controls are set to unity gain.. And you overload the input they should show the overload in the meter section.. Why because the input is not being attenuated by the gain control so if we are sure the input buffer is at unity and in most cases it is. And we know our gain control is at unity then we should be able to see a "real" level being reflected by the meter providing its accurate :)

So yes you are correct. Unity gain will show us that the input is being overloaded. The problem for overload comes in when you are using the gain to "attenuate" the input below unity gain then you can "trick" The meters into showing a signal as being lower than it really is.
« Last Edit: December 28, 2011, 11:41:30 AM by Church-Audio »
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Re: The myth of unity gain
« Reply #51 on: December 28, 2011, 11:45:34 AM »
LOL.  If we get this basic concept repeated about 30 different ways in 20 different languages, at some point I'll be able to pass an essay test instead of failing a multiple choice. 

 :coolguy:
« Last Edit: December 28, 2011, 11:47:15 AM by tonedeaf »

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Re: The myth of unity gain
« Reply #52 on: December 28, 2011, 11:57:22 AM »
It all comes back to what I have said for years - use the level that sounds best.  Though it can help to rule out obvious non-starters with simple testing - like the r09 and r09hr's problems distorting signal at lower trim settings.

It may be important to note that some recorders distort input at low trim settings even if they are not brickwalled.  That is my recollection, and it isn't worth the time to re-check.  In the case of the r09/r09hr, you are better to let it clip than to reduce the gain below the "line of death".

And to throw more gas onto the fire..... Some instruments are notorious for producing asymmetric waveforms.  Horns, for example, often produce waveforms with large peaks but shallow bottoms.  How does the recorder handle those at various settings?  Does the digital attenuation introduce artifacts?  Each recorder is different.

Less talk, more testing and comp'ing :P

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Re: The myth of unity gain
« Reply #53 on: December 28, 2011, 12:41:13 PM »
^^

Yes, a lot of wisdom there.  I was thinking of responding with a ton of uber-geek stuff (and might still), but this is the bottom line.

I think this thread started off with the idea of being sure the recorder was acting "normally" -- for example, not getting into the realm of distortion or "brickwalling" or whatever -- but beyond that, you just want to have your recorder, and your whole recording system, sound good.  That means testing, trying things out, listening, and deciding what you think sounds best.
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Re: The myth of unity gain
« Reply #54 on: December 28, 2011, 04:05:55 PM »
On Vanark's point about finding the most neutral input setting, I think that is a good idea to do, I just don't know if it is necessarily the unity gain point.  Like itgoes11 says, the way to get there might better be to listen to what sounds best.

The signal path in a recorder or preamp could be going through a number of capacitors, passive attenuators/resistors, active gain stages, etc.  Who knows how the signal is affected by all those components, and what sounds best?  I wouldn't say that it isn't necessarily a bad starting point to begin setting levels at unity gain, and listening to what it sounds like there and then at other gain settings, but I also don't know or assume that the unity gain point is where it will sound most neutral.

Ok, here goes the uber-geeky stuff, but I'll try to walk through it slowly (and I'll use pictures!).  Like I said, there could be lots of elements in the signal path, but consider the op amp gain stage (probably most/all of the recorders we use will have at least one active gain stage using an op amp or something akin to it). 

There are lots of factors affecting the sound of an op amp, and most of these are characterized by the manufacturers.  Among other things, this might include noise performance, slew rate, signal response, etc, and these characteristics might/will change depending on what gain setting you have on the op amp -- that is, unity gain (gain factor of 1, or 0db gain), gain of 2x (6db gain), gain of 10x (20db gain).

Below I've got some graphs and oscilloscope outputs provided in the datasheets for the Burr-Brown OPA2132 op amp and Analog Devices AD823 op amp (good op amps, though probably a bit dated).  These graphics represent how the op amp manufacturers characterize the response of their op amps.

First:  noise performance.  In the figure below you can see that at a gain of 1 (unity gain, 0db gain), the noise performance is about 0.0001%, whereas at a gain of 10 (20db of gain), the noise performance is about 0.001%.  That is, at 20db of gain, the noise performance is 10 times worse than it is at unity gain -- though the noise performance in either case is very, very good (and you'd be unlikely to discern a difference).




Next up: slew rate.  Slew rate represents how fast the output voltage changes in response to changes in the voltage of the input signal.  Higher values are better.

In the figure below, you can see that the slew rate at a gain of +10 (20db gain) is higher (better) than it is at a gain of +2 (6db of gain), which are both higher than the slew rate at a gain of 1 (unity gain).  In all cases, the slew rate is sufficiently high that the differences wouldn't have any discernible difference in sound (I wouldn't think anyway), but the slew rate response is better at higher gains than it is at unity gain.



Next figures:  small and large signal response, and overshoot.  If for instance you send an input of a square wave, you would ideally want to get an output of a square wave.

The figure below is an oscilloscope output of a small signal response of an op amp set to unity gain.  As you can see, what should be a square wave isn't perfectly square:  The signal rise and fall points should be straight up and down, but instead they are actually a steep ramp up and a steep ramp down.  On top of that, you can see the results of "overshoot" where the output signal rises too far and needs to correct itself, and falls too far and needs to correct itself.



The figure below shows overshoot as a percentage for small signal responses, for gains of 1 (unity) and 10 (20db) -- higher means more overshoot, or worse performance.  As you can see, performance is worse at unity gain than it is for a gain of 10, or a 20db gain.




Finally, large signal response.  Again, these use square wave inputs (on top) and show the resulting output (on bottom), which ideally should also be a square wave.  The first figure is the large signal response at a gain of 1 (unity gain), the second figure shows the large signal response at a gain of 10 (20db gain).  As you can see, the large signal response is better (more like a square wave) when the op amp is set for a +20db gain than when it is set for unity gain.





Bottom line, the info from the manufacturers spec sheets indicate that the op amps, not surprisingly, aren't perfectly ideal -- as in, perfectly neutral.  But the op amps are more neutral if you will, when considering signal noise when set for unity gain than when set for a gain of 10 (20db of gain).  On the other hand, the op amps are better/more neutral when set at higher gains rather than being set at unity when you are looking at slew rate, overshoot, and small and large signal response.  I'd guess though that in all cases, it is all just a matter of degree and that for all these performance metrics the op amps perform perfectly good regardless of whether they are run at unity gain or at +20db gain.

So which of the different op amp characteristics most impact the resulting sound, and lead to it sounding more neutral?  I couldn't tell you, but it seems like op amp response isn't universally better at unity gain than it is when set for a gain of +20db.  So I wouldn't assume it will sound more neutral at unity gain -- need to just listen for yourself at unity and at different gain settings and make your own judgements.

Hopefully I've got all that right with interpreting the spec sheets and mshilarious won't come in here saying I've screwed it all up.   :P
Mics: Microtech Gefell m20/m21 (nbob/pfa actives), Line Audio CM3, Church CA-11 cards
Preamp:  none <sniff>
Recorders:  Sound Devices MixPre-6, Sony PCM-M10, Zoom H4nPro

Offline hi and lo

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Re: The myth of unity gain
« Reply #55 on: December 28, 2011, 04:23:46 PM »
Great post, Todd! The first convincing argument to completely throw the concept of unity gain out the window. I think running at unity gain is still good as a best practice concept, but one cannot assume it is the absolute sweet spot in terms of performance or coloration.

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Re: The myth of unity gain
« Reply #56 on: December 28, 2011, 05:06:27 PM »
That's an excellent summary of the vagaries of op-amp performance.  Unless I am mistaken, one further gotcha is that most of the handhelds don't use op-amps in the traditional sense - they use highly integrated multi-function chipsets that include the a/d.  That's how they get the tiny form-factor and low power consumption.  There is also some question whether any of the gain is done in the digital domain.   Sound Devices has historically declined to reveal how much of their gain is analog vs. digital.

Another sore point with basing unity off the headphone output is that it assumes a lot about the headphone output gain structure.  And even whether the headphone output is before the a/d, or after.  In the 7xx recorders the headphone output signal path is a/d > d/a > amp > headphone out.



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Re: The myth of unity gain
« Reply #57 on: December 28, 2011, 05:58:31 PM »
I think running at unity gain is still good as a best practice concept, but one cannot assume it is the absolute sweet spot in terms of performance or coloration.

Remember that you can enter settings on your device which achive unity gain though it, but which may be very poor performing and terrible choices from a signal-to-noise perspective.  As mentioned previously, on a device with both input and output gain controls, there is not just one unity gain point, but a whole range of settings that offset each other to achieve unity gain.  Some of them are very poor choices.  (For instance, on the original R-09 you could turn the input gain all the way up to 30 and the line-out/headphone gain down low enough to compensate for that, so the same signal level was present at the line-input jack and line-out/headphone jack.  But that would be very noisy)

Another sore point with basing unity off the headphone output is that it assumes a lot about the headphone output gain structure.  And even whether the headphone output is before the a/d, or after.  In the 7xx recorders the headphone output signal path is a/d > d/a > amp > headphone out.

All true, but 'unity-gain' just means no gain change of the system, so input level is equal to output level.  The 'system' might be be a single op-amp, or an entire collection of circuits in a box.  Regardless, the system is at unity-gain when it's input level = output level. That the term 'unity-gain' doesn't really apply to a device like a recorder where the output is a digital file and not an electrical signal at an output bus or jack is the entire point of this thread.

Getting closer to what we are looking for, there is a large range of settings that achieve a good signal-to-noise ratio and will all work equally well (or nearly so in pratical terms), not just a single setting.  (Think input gain settings somewhere between 9 and 18 on the original R-09, the safe zone between between the extreme settings that cause distortion or excess noise)

If what you want to find is a single reference input-gain setting for an all-in-one recorder, and the manufacturer doesn't tell you what that setting is >:(, the way to go about it is to 1st select the appropriate reference level and choose a desired amount of headroom, make sure that reference level is within the good signal-to-noise range of the particular input and mode chosen on the recorder, input a test signal of that reference level and adjust the input gain until the meter reads your desired amount of headroom below 0dBFS. (Think input gain setting of 13 on the original R-09.  Though I'm not sure exactly what reverence level that setting is, it was determined to be the defacto 'reference input gain setting' for that machine, comfortably within the good signal-to-noise range, and incorrectly identified around here as the 'unity-gain' setting)
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Re: The myth of unity gain
« Reply #58 on: December 31, 2011, 09:38:32 AM »
Hi all,

remember my post in the "hiss with preamp" thread lately?

"There is another point that irritates me: the obsession with "unity gain". This is only meaningful if you have access to line input AND line output and if you want to use your device in a chain of other devices as a kind of "signal repeater".

For all other purposes, the only relevant level is 0dBFS, the point where hard clipping starts. Whenever I record a sound source, I set the gain control until I have optimum level with enough headroom to 0dBFS to avoid clipping. The *exact* value of gain or attenuation is not relevant for me, because the S/N ratio is specified *at the A/D input*. I use *optimum gain* instead of unity gain, and that concept is also used by all professionals I know.

On my PCM-M10 I set its line input level so that the 0dB test tone from my MixPre D gives a VU meter display of -24dBFS on the M10, this leaves enough headroom for unexpected level excursions even when using the limiter of my MixPre D. I then set the gain on the MixPre D to whatever the situation requires.

Greetings,

Rainer"

I feel vindicated by DSatz  >:D

BTW the mic preamp in the Sony PCM-D50 uses variable gain: the level control is a four-gang pot, two of the pots are used to set the mic preamp gain (non-inverting amp with opamp, variable resistor between output and inverting input), the mic attenuation switch changes between two resistor values from the inverting opamp input to ground.
The two other pots attenuate either the line input or the mic preamp output, and feed the resulting signal to the A/D converters via buffer amps. The mic pre is an Analog Devices ADA4841, not a bad chip, especially when powered with enough voltage to achieve excellent headroom.

The schematic for the input stage of the D50 can be found on page 25 of the service manual.

I suspect the M10 uses a similar input stage, because the same four-gang pot is used. I felt no urge to open my M10 and check it, but somebody else placed photos of a dismantled M10 on the net where this gain pot is clearly visible.

Both devices are known for rather robust mic inputs, that tolerate very high input levels. I measured the following input levels on the D50, the onset of clipping was verified by ear (and the ear was calibrated with RMAA  ;D)

D50, mic attenuator "0dB", clipping level 350mVRMS
VU level 0dB: Gain setting 10 0.5mVRMS   5 17.4mVRMS  3 191.6mVRMS

D50, mic attenuator "-20dB", clipping level 1.89VRMS (!)
VU level 0dB: Gain setting 10  5.5mVRMS  5 141.7mVRMS  3 1243mVRMS

D50, line in, clipping level not found since the signal generator only reached 2.3VRMS (-14dB on the VU meter)
VU level 0dB: Gain setting 10 369mVRMS  5 2160mVRMS  3 not enough signal generator output!

I will repeat those measurements with my M10, if there is interest in this group.

BTW I would not go below "1" on the gain setting, because the stereo tracking of ganged audio pots is not very good at that setting and below.


Greetings,

Rainer
recording steam trains since 1985

Offline Brian E.

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Re: The myth of unity gain
« Reply #59 on: July 16, 2015, 12:40:26 AM »
bookmarking to read later
my tapes:  The Archive | Dime | Etree

Recorder - Sony PCM A-10 | Cans - Shure SE535 | Mics - CA-14 Cards | Canon EOS 5D Mark II 17-40L f4 50 f1.4 70-200L f2.8 IS II 430EX II

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Re: The myth of unity gain
« Reply #60 on: August 22, 2015, 12:41:01 PM »
Its funny / sad that I gave this explanation many years ago here. Unity gain the concept is simple. I know this concept from mixing on a mixer. What goes in = what goes out = Unity gain. I have always told my customers to set the recorders they use to unity gain if they are going to use my preamps with their recorders. Anyone that is doing live recording and using external preamps should understand the concept of unity gain I hope.

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Re: The myth of unity gain
« Reply #61 on: August 29, 2015, 05:51:09 PM »
Hi, Church-Audio. Yes, the "unity gain" concept is simple, and with simple consumer recording equipment that's designed to work well together from A to Z (and as you said, with mixer channels), it's potentially useful. But people need to understand when it applies and when it doesn't, what benefit it can give and what benefit it can't and doesn't give.

Unfortunately, people here were citing this concept as if it was some kind of higher knowledge, when it's really just a quick rule of thumb for initial, quick and dirty settings that could be "in the ballpark" in many cases. A user who mistakes an easy practical suggestion for some kind of fundamental principle is a user who doesn't know when it's safe to rely on that suggestion and when it's not.

That's the problem. People here use wild combinations of pro, "semi-pro" and consumer equipment that were never designed to work together. Their consumer mindset leads them to expect those combinations to work, with maybe an adapter cable thrown in. For example, many people here use balanced, high-output professional condenser microphones at loud shows, and they want to feed those signals to the unbalanced inputs of consumer recording equipment where the input stage is likely to offer only two choices: one that's likely to be overloaded, and the other that's likely to have excess noise. "Unity gain" settings are useless in that situation; it's problematic from the get-go. It's dealable-with on a case-by-case basis, and some general principles apply, but it's not a situation where people should be encouraged to rely on "rules of thumb" in my opinion.

I'm not in the business of selling anything, so to me, the consumer expectation that things will be easy and automatic is, to my mind, a big part of the problem. Some people treat their ignorance almost like a privilege. But to make competent recordings reliably, there's a certain minimum amount of knowledge that the user needs to have and to apply. Some is elementary theory, while some is knowing the particular equipment that one is working with. It's not a whole lot of knowledge, and it doesn't have to be painful to learn; many people find it enjoyable and interesting.

--best regards
« Last Edit: August 29, 2015, 05:54:32 PM by DSatz »
music > microphones > a recorder of some sort

Offline Church-Audio

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Re: The myth of unity gain
« Reply #62 on: August 30, 2015, 03:50:54 PM »
Again you are always one of the most intelligent people I know in this business the way you put your thoughts into words is nothing less than art it self. Not kissing your ass lol just pointing out a fact many have pointed out here before. I am members of many forums besides this one some like this one have extreamly intelligent people as part of the group. I am always amazed at how well you put things into words. Its been said many times already but....Thank you for your contribution here.
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Offline DSatz

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Re: The myth of unity gain
« Reply #63 on: August 30, 2015, 06:20:29 PM »
um, gosh. I'm at a complete loss for words. (It's like one of those time-travel paradoxes, because you've made it so that now, I can't possibly deserve what you wrote.)

But seriously, thank you for the kind words and I hope it's clear that as a default starting point, when consumer gear is feeding signals to other consumer gear, or pro gear is feeding signals to other pro gear (but NOT when those two realms are mixed), the "unity gain" approach can give folks a nice starting point in a lot of cases. But I think sometimes that people don't even recognize when they're mixing stuff up like that, because they expect stuff to "just work" in the simplest way possible.

Which is basically a fair expectation where consumer gear is concerned--but for pro gear, or for mixed setups, no--a person really has to know the issues involved in getting stuff to work together.

--best regards
music > microphones > a recorder of some sort

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Re: The myth of unity gain
« Reply #64 on: November 27, 2015, 04:24:41 PM »
I have read this entire thread. I am looking into using the tascam ixj2 pre amp since I am interested in recording using my iPhone.
I don't really understand much of the things mentioned here but the general idea I got is voltage in = voltage out. Now firstly I am wondering how do recorders with a built in pre amp without adjustable volume knobs figure out the correct setting? I use church audio 11 mics and a Sony pcm m10 recorder and all I have to worry about is mic in, - 20 db setting and make sure the recording volume doesn't go over in the red.
Why don't pre amps have that built in auto function general recorders have? Wouldn't it make things ten times easier?
But since it is there I will have to deal with it and figure out the correct settings.
How do I find the correct voltage from the ca 11 mics ? And also what software to use to determine the voltage out?
Also, this pre amp has a limiter. Do I use the limiter on the unit, or the limiter on the software app( like the tascam pcm Rec mkII). Or both ? I record loud metal so it needs a limiter for sure.
Also lets say I put the level too low on the pre amp. Does it really matter since the recording levels on the recorder, in this case the iPhone , will be set correctly and a little higher since the pre amp is too low. Is it something you will
really notice ?

I appreciate any help. I am completely new to pre amps so it is very interesting.
But I have to say, I don’t mind it. I do object when I see people sticking microphones up my nose, in the front row. If I see anyone doing that [laughs] I’m going to have security remove them. Because that’s just obnoxious. But I don’t mind if people come and discreetly at the back make a recording of it. And I know that it’s just for their own use, for the superfan.
(Steven Wilson , interview http://blog.musoscribe.com/index.php/2011/01/25/interview-steven-wilson-on-audience-taping/ )

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Re: The myth of unity gain
« Reply #65 on: November 27, 2015, 05:01:48 PM »
I have read this entire thread. I am looking into using the tascam ixj2 pre amp since I am interested in recording using my iPhone.
I don't really understand much of the things mentioned here but the general idea I got is voltage in = voltage out. Now firstly I am wondering how do recorders with a built in pre amp without adjustable volume knobs figure out the correct setting? I use church audio 11 mics and a Sony pcm m10 recorder and all I have to worry about is mic in, - 20 db setting and make sure the recording volume doesn't go over in the red.
Why don't pre amps have that built in auto function general recorders have? Wouldn't it make things ten times easier?
But since it is there I will have to deal with it and figure out the correct settings.
How do I find the correct voltage from the ca 11 mics ? And also what software to use to determine the voltage out?
Also, this pre amp has a limiter. Do I use the limiter on the unit, or the limiter on the software app( like the tascam pcm Rec mkII). Or both ? I record loud metal so it needs a limiter for sure.
Also lets say I put the level too low on the pre amp. Does it really matter since the recording levels on the recorder, in this case the iPhone , will be set correctly and a little higher since the pre amp is too low. Is it something you will
really notice ?

I appreciate any help. I am completely new to pre amps so it is very interesting.

I can tell you that my mics.. are going to put out about -35 db @ 1k at 114 db on axis less then an inch from the diaphragm with a distortion of less then 0.5% THD. So if you are in the average concert close to the stacks that level that I test the mics at is very similar to what you might encounter. That means with out any gain applied to my mics you are going to be running around -35 to -30 or there about. My whole thing about live recording is making sure you leave about 10 db for headroom on your VU meter. If you find out what unity gain is on your recorders line input you might need to apply 20 db of gain or 15 db of gain to get close to that -10 db Vu reading. So in a situation where things are quiet like 100 db or less you might need even more gain like 20  or 30 db of gain.. Again heeding the -10 db rule for headroom on your VU meter. Setting the preamp so that you get what you need to sit around -10 to -8. With a unity gain setting again on your recorders input.. The whole point of the preamp is  A good signal to noise ratio B easier to adjust then a recorders input in some cases. And proper power for my mics.. If you want to be able to measure the output level of my mics.. You need a calibrated noise source meaning a source of noise that has a known acoustic level at a known distance. Then you can measure the voltage output or connect it to a computer that has a calibrated unity gain input. Its not a very easy thing to do. I have all of this test gear so I can do this quite easily. It starts with a calibrated known audio source. For your application it would be overkill and not really practical. So to recap.

You want to know what unity gain is for your recorders input you plan on using..
You want to know how much "make up gain" you need to get you to where you want to be on your VU meter. And the other issue is you want to hope that your VU meter is calibrated to Unity gain :) Its a complex subject and I really do suck at explaining things in written txt. Sorry I did my best. I hope this helps you somewhat.
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Offline Ekib

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Re: The myth of unity gain
« Reply #66 on: November 28, 2015, 02:51:48 PM »
I have read this entire thread. I am looking into using the tascam ixj2 pre amp since I am interested in recording using my iPhone.
I don't really understand much of the things mentioned here but the general idea I got is voltage in = voltage out. Now firstly I am wondering how do recorders with a built in pre amp without adjustable volume knobs figure out the correct setting? I use church audio 11 mics and a Sony pcm m10 recorder and all I have to worry about is mic in, - 20 db setting and make sure the recording volume doesn't go over in the red.
Why don't pre amps have that built in auto function general recorders have? Wouldn't it make things ten times easier?
But since it is there I will have to deal with it and figure out the correct settings.
How do I find the correct voltage from the ca 11 mics ? And also what software to use to determine the voltage out?
Also, this pre amp has a limiter. Do I use the limiter on the unit, or the limiter on the software app( like the tascam pcm Rec mkII). Or both ? I record loud metal so it needs a limiter for sure.
Also lets say I put the level too low on the pre amp. Does it really matter since the recording levels on the recorder, in this case the iPhone , will be set correctly and a little higher since the pre amp is too low. Is it something you will
really notice ?

I appreciate any help. I am completely new to pre amps so it is very interesting.

I can tell you that my mics.. are going to put out about -35 db @ 1k at 114 db on axis less then an inch from the diaphragm with a distortion of less then 0.5% THD. So if you are in the average concert close to the stacks that level that I test the mics at is very similar to what you might encounter. That means with out any gain applied to my mics you are going to be running around -35 to -30 or there about. My whole thing about live recording is making sure you leave about 10 db for headroom on your VU meter. If you find out what unity gain is on your recorders line input you might need to apply 20 db of gain or 15 db of gain to get close to that -10 db Vu reading. So in a situation where things are quiet like 100 db or less you might need even more gain like 20  or 30 db of gain.. Again heeding the -10 db rule for headroom on your VU meter. Setting the preamp so that you get what you need to sit around -10 to -8. With a unity gain setting again on your recorders input.. The whole point of the preamp is  A good signal to noise ratio B easier to adjust then a recorders input in some cases. And proper power for my mics.. If you want to be able to measure the output level of my mics.. You need a calibrated noise source meaning a source of noise that has a known acoustic level at a known distance. Then you can measure the voltage output or connect it to a computer that has a calibrated unity gain input. Its not a very easy thing to do. I have all of this test gear so I can do this quite easily. It starts with a calibrated known audio source. For your application it would be overkill and not really practical. So to recap.

You want to know what unity gain is for your recorders input you plan on using..
You want to know how much "make up gain" you need to get you to where you want to be on your VU meter. And the other issue is you want to hope that your VU meter is calibrated to Unity gain :) Its a complex subject and I really do suck at explaining things in written txt. Sorry I did my best. I hope this helps you somewhat.

Thanks for the explanation! I will have to read it a couple times to understand everything but I surely get some idea.
It really is complex indeed.
Still I am wondering why separate preamps have the volume options and built in pre amp's don't.
And do I need to use the limiter on the pre amp itself or the limiter on the app?
But I have to say, I don’t mind it. I do object when I see people sticking microphones up my nose, in the front row. If I see anyone doing that [laughs] I’m going to have security remove them. Because that’s just obnoxious. But I don’t mind if people come and discreetly at the back make a recording of it. And I know that it’s just for their own use, for the superfan.
(Steven Wilson , interview http://blog.musoscribe.com/index.php/2011/01/25/interview-steven-wilson-on-audience-taping/ )

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Re: The myth of unity gain
« Reply #67 on: November 29, 2015, 02:40:03 PM »
Why don't pre amps have that built in auto function general recorders have? Wouldn't it make things ten times easier?

Auto level setting is similar to a limiter. Both monitor the input level to the device and adjust the output level. In the case of a recorder, the output level is the recorded level.  Both can be useful as a "crutch" to help get a usable recording if you are unable to set the recording level correctly, if the sound source being recorded is too unpredictable.

Auto-record level constantly adjusts the recording level, which can be useful for recording lectures or speech where the intent  of the recording is transcription without needing to pay too much attention to the recording, rather than natural and pleasing  sounding audio quality.  It is not a good choice for recording music, where it will be constantly trying to make the louder parts quieter and the quiet parts louder, but cannot do so very smoothly.  You will hear it working, like someone constantly turning the volume up and down, clumsily.  If you set your recording level correctly so that there is enough room to fit the music, you don't need auto-level setting. 

A limiter on a preamp or recorder can be useful for music recording if the recording level has been set high enough that the signal would overload and distort badly during quick (transient), high level peaks.  A limiter is not designed to be constantly engaged, it should only "do it's thing" momentarily, and then release quickly.  If it is only working occasionally, its effect will not be as audibly apparent as the auto-level setting function.  But if it is working at all, it is reducing the full natural range of the music.  If you set the recording level low enough so that there is enough room for the peaks without overloading, you don't need a limiter. 

You can make better recordings by setting your recording level appropriately so that you do not need to use either of these things on the recorder.

Quote
Do I use the limiter on the unit, or the limiter on the software app( like the tascam pcm Rec mkII). Or both ? I record loud metal so it needs a limiter for sure.

Limiting after the recording has been made serves an entirely different function.  It is used to increase the apparent loudness of the recording beyond what one could do by simply turning up the signal level until it is just below overload.  There is no need to do that to prevent distortion.  Doing so actually introduces distortion.

You won't need a limiter "for sure".  A limiter isn't useful because the sound being recorded is loud.  You can simply turn down the recording level to fully accommodate "loud".  A limiter is useful when the overall range of loudness is very large and hard to predict.  With loud metal, the average level is very loud, yet the overall range of loudness during the music is not very large- the peak levels aren't going to be a whole lot higher than the average loudness level.  It gets loud and stays loud.  It doesn't have very rapid, very high peaks that are considerably louder than most of the music. 

Set your levels so that you can accommodate the highest peaks without overload and leave some safety margin.  You probably won't notice any low-level noise introduced by your equipment during the quiet parts.  They aren't going to be quiet enough to hear the noise.

Quote
Also lets say I put the level too low on the pre amp. Does it really matter since the recording levels on the recorder, in this case the iPhone , will be set correctly and a little higher since the pre amp is too low. Is it something you will really notice ?

That's "gain-staging", and really what this thread is all about.  It's all about setting the relative levels through each device correctly so that everything works as best it can- neither causing distortion of the signal nor introducing noise.  It matters if the gain-staging is set inappropriately and causes either of those problems. It doesn't matter if neither of those problems are introduced.  There is usually a range of settings which will not introduce either of those problems, and they only become a problem when your gain-staging falls outside of that acceptable range.  Setting optimal gain-staging makes the breadth of that range as wide as possible.

Once you have a raw recording which is neither clipped at the top (from a level being set too high somewhere) or buried in noise (from a level being set too low somewhere), you can adjust the level and "loudness" afterwards with editing software however you like.  Doing that is the topic for another thread.
« Last Edit: November 29, 2015, 02:43:40 PM by Gutbucket »
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Ekib

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Re: The myth of unity gain
« Reply #68 on: December 01, 2015, 01:10:40 PM »
Thanks for your answers!

Quote
Auto level setting is similar to a limiter. Both monitor the input level to the device and adjust the output level. In the case of a recorder, the output level is the recorded level.  Both can be useful as a "crutch" to help get a usable recording if you are unable to set the recording level correctly, if the sound source being recorded is too unpredictable.

Auto-record level constantly adjusts the recording level, which can be useful for recording lectures or speech where the intent  of the recording is transcription without needing to pay too much attention to the recording, rather than natural and pleasing  sounding audio quality.  It is not a good choice for recording music, where it will be constantly trying to make the louder parts quieter and the quiet parts louder, but cannot do so very smoothly.  You will hear it working, like someone constantly turning the volume up and down, clumsily.  If you set your recording level correctly so that there is enough room to fit the music, you don't need auto-level setting.

I actually thought the limiter would be the same as the -20 DB switch that some recorders have . I thought the limiter would be automatically attenuating the signal -20Db ( what usual attenuation switches do ). So it's good you cleared that up for me. I certainly don't need auto level, I didn't know that's what a limiter does!
So when I use my tascam pre amp ixj2 along with my church audio 11 mic's , would I need an attenuation cable in between the pre amp and the mic's ?
Or since I use my i-Phone and the pre amp works like an AD converter the input can't be overloaded ? I really have no clue. What I mean is that I have always used -20 DB at my current PCM M10 , and before on Minidisc and DAT recorders. What should I do?



Quote
Do I use the limiter on the unit, or the limiter on the software app( like the tascam pcm Rec mkII). Or both ? I record loud metal so it needs a limiter for sure.



Quote
Also lets say I put the level too low on the pre amp. Does it really matter since the recording levels on the recorder, in this case the iPhone , will be set correctly and a little higher since the pre amp is too low. Is it something you will really notice ?

That's "gain-staging", and really what this thread is all about.  It's all about setting the relative levels through each device correctly so that everything works as best it can- neither causing distortion of the signal nor introducing noise.  It matters if the gain-staging is set inappropriately and causes either of those problems. It doesn't matter if neither of those problems are introduced.  There is usually a range of settings which will not introduce either of those problems, and they only become a problem when your gain-staging falls outside of that acceptable range.  Setting optimal gain-staging makes the breadth of that range as wide as possible.[/quote]

My ixj2 has a small level meter which shows green and goes to red when the signal gets distorted. As long as I have the green light I suppose it's ok?

Thanks again for the input!
« Last Edit: December 01, 2015, 01:30:07 PM by Ekib »
But I have to say, I don’t mind it. I do object when I see people sticking microphones up my nose, in the front row. If I see anyone doing that [laughs] I’m going to have security remove them. Because that’s just obnoxious. But I don’t mind if people come and discreetly at the back make a recording of it. And I know that it’s just for their own use, for the superfan.
(Steven Wilson , interview http://blog.musoscribe.com/index.php/2011/01/25/interview-steven-wilson-on-audience-taping/ )

Online Gutbucket

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Re: The myth of unity gain
« Reply #69 on: December 01, 2015, 05:50:23 PM »
So when I use my tascam pre amp ixj2 along with my church audio 11 mic's , would I need an attenuation cable in between the pre amp and the mic's ?
Or since I use my i-Phone and the pre amp works like an AD converter the input can't be overloaded ?

Quote
My ixj2 has a small level meter which shows green and goes to red when the signal gets distorted. As long as I have the green light I suppose it's ok?

Well the bad news is that you can overload a device's analog input stage, and/or overload it's AD converter!  Sometimes on inexpensive equipment you can overload the analog input stage but not the AD stage, and the meters will indicate good levels without indicating the overload.  That's commonly referred to around here as "brickwalling".  If susceptible to "brickwalling distortion" and fed an overly hot input, a user will adjust the device's input level knobs below a certain level in an attempt to keep the device's meter from showing overload, but the input-stage has already distorted badly.  Most inexpensive recorders used around here have a practical "do not go below" level on their input level knobs, which users here figure out pretty quickly and it then becomes common knowledge.  I have no idea if that's the case or what that that position of the input level knob might be on this Tascam i-phone interface, but if you need to set the level knobs overly close to the bottom of their range in order to avoid the meter indicating overload, it might be an issue.   If the Tascam has a separate line-level input which still provides power to the mics, or lets you switch it's mic-level input to a line-level input while keeping mic power on, then that will allow a hotter input and probably 'fix' the brickwalling problem if there is one.  Alternately you could use an attenuator cable into the mic-level input, but it would need to be one which passes sufficient mic-power to power the microphones correctly.

But from what Chris Church posted above about the sensitivity and output level of his microphones, you probably won't have a problem going straight in.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Ekib

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Re: The myth of unity gain
« Reply #70 on: December 03, 2015, 04:23:35 AM »
Quote

Well the bad news is that you can overload a device's analog input stage, and/or overload it's AD converter!  Sometimes on inexpensive equipment you can overload the analog input stage but not the AD stage, and the meters will indicate good levels without indicating the overload.  That's commonly referred to around here as "brickwalling".  If susceptible to "brickwalling distortion" and fed an overly hot input, a user will adjust the device's input level knobs below a certain level in an attempt to keep the device's meter from showing overload, but the input-stage has already distorted badly.  Most inexpensive recorders used around here have a practical "do not go below" level on their input level knobs, which users here figure out pretty quickly and it then becomes common knowledge.  I have no idea if that's the case or what that that position of the input level knob might be on this Tascam i-phone interface, but if you need to set the level knobs overly close to the bottom of their range in order to avoid the meter indicating overload, it might be an issue.   If the Tascam has a separate line-level input which still provides power to the mics, or lets you switch it's mic-level input to a line-level input while keeping mic power on, then that will allow a hotter input and probably 'fix' the brickwalling problem if there is one.  Alternately you could use an attenuator cable into the mic-level input, but it would need to be one which passes sufficient mic-power to power the microphones correctly.

But from what Chris Church posted above about the sensitivity and output level of his microphones, you probably won't have a problem going straight in.

I think I will do a test at a not important for me show.
I have never had problems with brickwall since I always used the -20DB switch on recorders. But the Tascam doesn't have that so I will have to see.
Maybe I will have to get an attenuator cable. They are no cheap though. Any recommendations for a good one? I know core sound makes one.
Thanks again for the help.
But I have to say, I don’t mind it. I do object when I see people sticking microphones up my nose, in the front row. If I see anyone doing that [laughs] I’m going to have security remove them. Because that’s just obnoxious. But I don’t mind if people come and discreetly at the back make a recording of it. And I know that it’s just for their own use, for the superfan.
(Steven Wilson , interview http://blog.musoscribe.com/index.php/2011/01/25/interview-steven-wilson-on-audience-taping/ )

Offline Ekib

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Re: The myth of unity gain
« Reply #71 on: December 28, 2015, 01:57:31 PM »
Quote
Well the bad news is that you can overload a device's analog input stage, and/or overload it's AD converter!  Sometimes on inexpensive equipment you can overload the analog input stage but not the AD stage, and the meters will indicate good levels without indicating the overload.  That's commonly referred to around here as "brickwalling

This turned out to be so correct. I tested the IXJ2 Tascam preamp with the IPhone 5S at a local show ( coverband playing ).
The first song I recorded with the IXJ2 at level 2, than every next song I added a level. So 3,4,5 etc. As you see on the added file the first 6 songs look ok ( and the have no brickwall, distortion ). I adjusted the recording level on every song at the iPhone using the Tascam PCM app.
Than when I arrived at level 8 it started to distort. At level 9 and 10 the distortion is really bad. The indicator however only indicated distortion at level 10. So Gutbucket , you were completely correct.
The recording turned out to be good sounding ( except of course the distorted songs ) . I actually don't hear any quality difference in songs I recorded at level 2-7 .
I recorded two songs of the same band using my PCM M10. And after editing ( 96/24 to 44/16 ) I really don't hear any difference at all with the songs recorded with the IPhone.
So I think I will start at level 5 to be on the safe side for other shows.
I surely don't need an attenuator cable at all.
« Last Edit: December 28, 2015, 02:00:31 PM by Ekib »
But I have to say, I don’t mind it. I do object when I see people sticking microphones up my nose, in the front row. If I see anyone doing that [laughs] I’m going to have security remove them. Because that’s just obnoxious. But I don’t mind if people come and discreetly at the back make a recording of it. And I know that it’s just for their own use, for the superfan.
(Steven Wilson , interview http://blog.musoscribe.com/index.php/2011/01/25/interview-steven-wilson-on-audience-taping/ )

Online Gutbucket

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Re: The myth of unity gain
« Reply #72 on: December 28, 2015, 02:55:21 PM »
Good to hear you got it figured out.  And good methodology for determining at which settings the problem occurs.

Quote
  I actually don't hear any quality difference in songs I recorded at level 2-7.
So I think I will start at level 5 to be on the safe side for other shows.

This is basically sums up the issue surrounding gain-staging with these kinds of devices and small recorders. Typically there is most often a range of acceptable gain-staging settings which produce equally acceptable results.  Everything is good as long as the settings don't creep outside of that region.  Determining the "okay range" via your experiment and using the middle value of that range as your default setting is what this is all about.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Ekib

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Re: The myth of unity gain
« Reply #73 on: December 30, 2015, 02:24:49 PM »
Good to hear you got it figured out.  And good methodology for determining at which settings the problem occurs.

Quote
  I actually don't hear any quality difference in songs I recorded at level 2-7.
So I think I will start at level 5 to be on the safe side for other shows.

This is basically sums up the issue surrounding gain-staging with these kinds of devices and small recorders. Typically there is most often a range of acceptable gain-staging settings which produce equally acceptable results.  Everything is good as long as the settings don't creep outside of that region.  Determining the "okay range" via your experiment and using the middle value of that range as your default setting is what this is all about.

Why is it there is a range of acceptable gain staging settings on smaller recording devices ?

I was actually surprised the i-Phone in combination with the IXJ2 made such a great recording . I used the Church Audio 11 mic in this test.


But I have to say, I don’t mind it. I do object when I see people sticking microphones up my nose, in the front row. If I see anyone doing that [laughs] I’m going to have security remove them. Because that’s just obnoxious. But I don’t mind if people come and discreetly at the back make a recording of it. And I know that it’s just for their own use, for the superfan.
(Steven Wilson , interview http://blog.musoscribe.com/index.php/2011/01/25/interview-steven-wilson-on-audience-taping/ )

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Re: The myth of unity gain
« Reply #74 on: December 30, 2015, 05:12:00 PM »
The range of acceptable settings is actually even wider in high-quality equipment.  There is plenty of room to fit the music between noise way down at the quiet end of things, and distortion at the loud end of things.  Finding the most optimal setting is an admirable goal, and maximizes the range of what you can record without problems, but is somewhat academic and considerably less important than simply landing somewhere within that acceptable range.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline EricM

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Re: The myth of unity gain
« Reply #75 on: February 28, 2016, 06:56:00 PM »
I used a Sony M10, Audio Technica AT943 stereo cardioid mics and a 12volt battery box.

I had my rec dial on 4. Low Mic sensitivity, limiter on and manual record mode. Mic input used.

I still have some clipping in the loudest screams, yells and whistles from the audience. None of the music clipped as far as I could tell.  It's mostly a clean recording. I think over the 2 hour show there's maybe 2 minutes worth of clipping.

Next time I will set my Rec dial to 3. I don't want even 1 second worth of clipping.

Is there anything else I could have done?

Offline nulldogmas

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Re: The myth of unity gain
« Reply #76 on: February 28, 2016, 07:00:46 PM »
I used a Sony M10, Audio Technica AT943 stereo cardioid mics and a 12volt battery box.

I had my rec dial on 4. Low Mic sensitivity, limiter on and manual record mode. Mic input used.

I still have some clipping in the loudest screams, yells and whistles from the audience. None of the music clipped as far as I could tell.  It's mostly a clean recording. I think over the 2 hour show there's maybe 2 minutes worth of clipping.

Next time I will set my Rec dial to 3. I don't want even 1 second worth of clipping.

Is there anything else I could have done?

You've looked at the waveform to see that it's definitely clipping, as in there are peaks hitting 0dB? Would want to rule out that something isn't overloading earlier in the chain, though with a 12v battery box that admittedly seems unlikely.

Next option I'd use would be to switch to Line In, which is significantly quieter than the Mic In on the M10.

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Re: The myth of unity gain
« Reply #77 on: February 28, 2016, 08:47:39 PM »
^ I had a look at it in Audacity. There's some clipping there. Some red peaks. I listened to my recording at the same time as looking at the graph. In the screams etc there's definately clipping. I thought for sure I'd be safe at Rec Level 4 on the dial and the other settings. I might try Line In next time as you suggested. I've only recorded 3 shows so far. I know one things for certain for me and that is that 4 is too high.

Lucky for me I'm mostly in the right levels. I ended up with a pretty good recording that could have been great.
« Last Edit: February 28, 2016, 08:49:40 PM by EricM »

 

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