Topic: Analog Line-In: how to pre-determine overloading???

[twatts (pants are so over-rated...)]

I imagine there is a way to calculate if your recorder will overload via the analog line-in input based on dbUs, etc...   Can someone explain how this works to me???

I've been reading about the various Tascam Hand-Helds and comping them with the Edirols and Sonys.  It seems like the R09HR and the M10 can take a line-in of +26dbUs, while some of the Tascams can take +6dbUs???  If I decide to run a SD MP-2 in front of either unit, can I calculate at what point the hand-held input will overload???  I would imagine that would mean figuring out the output level of the SD MP-2 at each the various points on the output gain (zero gain on knob, half on, full-on), and comparing that to the max level of the recorder???

Thanks,

Terry

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I imagine there is a way to calculate if your recorder will overload via the analog line-in input based on dbUs, etc...   Can someone explain how this works to me???

I've been reading about the various Tascam Hand-Helds and comping them with the Edirols and Sonys.  It seems like the R09HR and the M10 can take a line-in of +26dbUs, while some of the Tascams can take +6dbUs???  If I decide to run a SD MP-2 in front of either unit, can I calculate at what point the hand-held input will overload???  I would imagine that would mean figuring out the output level of the SD MP-2 at each the various points on the output gain (zero gain on knob, half on, full-on), and comparing that to the max level of the recorder???

Yes, that's the process I used.

I did this once and use my 722 which (when at -6) clips at +26dbu. I then reset it to 0 gain and added 17db of gain which represented the signal (reading 0dbfs) that my mics send at the loudest point (in my 4 loudest shows exempting stage lip stuff). Made note of the signal and then put a pre-amp between the two, set the gain of the 722 to clip at 0 (as the preamp had a max of +20dbu) and then played the signal increasing gain until I heard distortion over the recording. Granted, I had little numbers on the preamp and it matched within a db or so, but the point is if you know the recorder's limits (and those limits are true), and you can recreate a tone entering the preamp that is the same level as the loudest point you would reasonably encounter, you can get benchmarks to where a given spot on the preamp is puting out Xdbu with your mics. Once you know that, you can switch out the recorder and repeat the test with a new variable (the recorder) and slowly wratchet up the gain until you either hit 0dbfs or you hear distortion while monitoring and see what that value is.

[twatts (pants are so over-rated...)]

Thanks for the reply.  I see what you are doing and that would work - if I already owned the gear...

The reason I want to know this is I've had a recent discussion on another board where someone is talking about buying a hand-held unit.  I don't have experience with analog line-in (I've always been a SPDIF guys), so I'm unsure how to figure out all the output dBVs and input dBVs:

What practical difference would having a line-in with a max input of -4dBV (Tascam DR-05) vs. +6dBV (Tascam DR-07) make???  I understand the basic idea that the +6 will take a hotter signal, but in terms of numbers, and in terms of possible Preamps, what does it actually mean???

In a more theoretical sense, since all this will really be a factor of how Loud the actual recording is, if I run a SD MP-2 (for example) in front of either Tascam mentioned above, how do I pre-determine approx. where I can I can expect the signal to overload???

The reason I want to know this is to determine which would be more practical in the long-run, if a Preamp was added in front of the recorder.

I guess I'm looking for the mathematics behind figuring out "levels".  I suppose I'm also looking for any recommendations in the hand-held arena - what is comparable to the DR-05/07 in functionality, but also price???

Thanks,

Terry

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Thanks for the reply.  I see what you are doing and that would work - if I already owned the gear...

fair enough, I missed that bit, sorry.

What practical difference would having a line-in with a max input of -4dBV (Tascam DR-05) vs. +6dBV (Tascam DR-07) make???  I understand the basic idea that the +6 will take a hotter signal, but in terms of numbers, and in terms of possible Preamps, what does it actually mean???

Ok, in general terms. My 722 hits max at +26dbu, the sonosax sx-m2 output max is +20dbu. The pmd-661 is something like +16dbu I think (someone else will know). My mics, which are hot are around +4dbu.

So converting the dbV to dbu, you get a sense that the DR-05 tops out at -1dbu or -2dbu and the DR-7 at around +8dbu. The korg mr-1 had a max input of about -2dbu and it (IME) routinely would overload with a sbd signal or a strong amp (I've seen people use 20db or greater attenuators with a V3). For example, if I were having to pair my mics (circa 34mv/pa, or a max out of +4dbu, which is hot) with either recorder, I could run a battery box and risk clipping on the DR-05 at really loud shows and add about +5db or so of gain on the preamp and run out of headroom of a couple db on the DR-07 (again, at really loud shows, quieter stuff adjusts accordingly).

Most pre-amps have a minimum operating gain. The sax when it's not in pass-through mode is +6db, the V3 is like +10 I think.

So the questions I'd have would be:
- whats the mv/pa rating of your mics? 14mv/pa is roughly 9dbu quieter than 35mv/pa at the same dbspl source.
- will you ever take a sbd patch or no?
- minimum gain on the pre-amp you like? (balanced/unbalanced ratings are nice)

The reason I want to know this is to determine which would be more practical in the long-run, if a Preamp was added in front of the recorder.

That's easy, search for a hot signal recorder if you like preamps, especially if you like lots of gain/coloration from preamps.

Make more sense?

[DSatz]

I am definitely overtired at the moment but I find this discussion hard to follow.

What I do is take a simple signal generator and set it to generate a tone at some level. I connect its output to the input of the recorder or preamp or mixer that I want to test, and I listen for distortion at the output of that device. If there's no audible distortion, I increase the generator's output level until I hear some.

Now, the question is whether that distortion is due to input overload or due to overload somewhere else further along in the circuitry (e.g. the input circuit is handling the signal OK, but the record level is cranked up so high that one or more internal circuit stages are being overdriven), or maybe both.

The easiest way to tell is by reducing the input gain (the "record level control") while keeping the signal level from the generator the same as before. If the distortion doesn't decrease and eventually go away, then the input (or some other fixed threshold near the input, which is the same thing in effect) is clipping. So I reduce the generator's signal level until the distortion just disappears--and whatever voltage that is, is the device's input overload point.

If, on the other hand, the distortion DOES go away when I reduce the input gain, I bring up the level of the generator again until either (a) I reach a signal level that causes distortion no matter how far I turn the input gain down (which means I've found the input overload point) or (b) I reach a signal level that's higher than I will ever need to feed in to that particular input. As far as possible, I only use equipment that gives me outcome (b).

It doesn't matter very much what units of measure we're using as long as we're using them correctly. They can be mV or dBu or dBV. If any of those units of measure give you trouble, pick one that doesn't. Decibel-based units can be very convenient, but only if you understand them and can convert between voltages and decibels-relative-to-some-reference-level. If that doesn't come easily to you, use mV; there's no shame in that.

--best regards

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I am definitely overtired at the moment but I find this discussion hard to follow.

My apologies, I unfortunately lack some of the appropriate gear to really test this sort of stuff, so my hillbilly method was the best I had. For posterity reasons at least, I appreciate the better answer. 

[Gutbucket]

Unashamed member of the mV camp here.

I have a cheap Behringer cable tester / signal generator which I route through a home stereo amp to use its volume knob as a level control.  I then simply measure the output of the amp with a digital multimeter set to read AC voltage in mV.

Lacking the signal generator, you can substitute a recorded test signal played back by computer, disc player or another recorder.

[F.O.Bean]

Yeah this is WAY over my head

[Todd R]

I hate almost even to chime in given all the great practical testing advice, but if you want to go the quick and dirty route using specifications and theory (a good route if you don't actually have the gear in question in hand).....

You should be able to pre-determine overloading using some math and mfg's specifications (I say "should" since many mfgs fail to provide the most basic of specs).

You need to consider:
- your mic sensitivity from the specs
- the max sound pressure level you expect at your show/where you're recording -- using a general rule of thumb or guess
- how much gain you'll be applying at the preamp
- the max input level at your recorder or A/D, again from the specs, if they'd only supply it.

If you put all the units in dbu or dbV, it is very easy.  Here is a handy calculator for conversions:

http://www.sengpielaudio.com/calculator-db-volt.htm

I prefer to work with the dbu unit, though dbV works as well.

Step 1:  Get your mic sensitivity from the specs.  It should be listed as a dbu per "Pascal" or mV per Pascal

If needed, use the calculator above to put the value into dbu.  A typical condensor mic will be something like -35 dbu/Pa.  if the spec comes in mV/Pa (millivolts), use the calculator above -- put the voltage spec in the 3rd column, being careful that the calculator wants volts, not millivolts.  So if your mic spec is 14.7 mV/Pa, put 0.0147 into the calculator.  In this case, you'll find it is -35 dbu/Pa

Step 2:  Determine or guess the SPL you'll be recording. 

For a loud PA-driven show, maybe a good guess is 120db, or maybe 124db.  Note:  this is very loud, but you want max instantaneous, unweighted SPL.  An averaged SPL level using A-weighting will probably be much less than this, but low bass frequencies are discounted by A-weighting.  (I'd really love to hear a good educated guess as to what un-weighted max SPL levels might be for a PA-driven concert with loud subwoofers banging -- I always guess at 124db).

To go forward, it is important to know that a Pascal = 94db.  So the mic spec of -35dbu per pascal says the mic will be putting out -35 dbu at 94db, we need to know how much it puts out at the max SPL.  So you'll want max SPL of 124db - 94db = an additional 30db

Step 3:  Determine how much gain in db you'll add using your preamp. 

this is easy, say you'll add 20db.  (Ok, easier for those using a Lunatec V2 or V3, since the knobs tell you the db gain.  For other preamps, guess based on the min and max gain the preamp can put out, and where you are on the gain knob.)

Say as an example, you've got a Beyer MV100 preamp with a minimum fixed gain of 20db -- so you're adding 20db of gain at the preamp

Step 4:  Get the max input level of your recorder from the specs.  Not all mfgs seem to want to provide this, but you can usually find someone on the interweb who has tested it.  GuySonic is great at doing this testing for us, and ts.com often has this figure for various recorders if you dig.

Say the recorder can take +24dbu (I think this is the figure for the Sony D50). Or maybe like the handheld Tascam units it is more like +6 dbu.

Step 5:  Determine if what you have in Steps 1-3 is too much for the recorder in step 4.

This is easy, just simple addition.  Just make sure if you've got specs on mic sensitivity in dbu, you compare it to recorder max input in dbu (not max volts or max dbV -- use the calculator if needed to convert).

For an example of a -35dbu mic sensitivity, an SPL of 124db, and 20db of gain, it is:

-35 + (124-94) + 20 = 15dbu

So in this case, you'd be golden if you were running the Sony D50 (max input of 124dbu) and screwed if you were running the Tascam DR07 (max input of +6dbu)



Again, this is a pretty easy way to guess if you'll overload overload your recorder given what you have for mics and what you have for a preamp.  Actual testing is much better, but if for instance you haven't yet bought the recorder and already have the mics and preamp (so you can't test, but would like to know if the recorder is a good purchase), this should get you in the ballpark to understand if you'll be overloading the recorder.