Topic: The myth of unity gain

[Church-Audio]

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.

[DSatz]

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

[Church-Audio]

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.

[DSatz]

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

[Ekib]

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.

[Church-Audio]

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.

[Ekib]

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?

[Gutbucket]

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.

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.

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.

[Ekib]

Thanks for your answers!

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?

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 ?

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!

[Gutbucket]

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 ?

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.

[Ekib]

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.

[Ekib]

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.

[Gutbucket]

Good to hear you got it figured out.  And good methodology for determining at which settings the problem occurs.

  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.

[Ekib]

Good to hear you got it figured out.  And good methodology for determining at which settings the problem occurs.

  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.

[Gutbucket]

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.