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Running an analog compressor on a DAW master bus output, level issues???
Old 11th February 2013
  #1
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Running an analog compressor on a DAW master bus output, level issues???

Just wanted to see if others are experiencing the same thing.

Let's say I want to run a stereo mix out of a DAW and then feed it into an analog compressor.

In my case, at the moment, I have an Apogee DA-16X here. According to the manual, the Apogees are factory calibrated so that -16dBFS = +4dBu. I did double check this using a 1kHz sine wave test tone and volt meter, -16dBFS yields very close to 1.2v at the outputs so it's certainly close in any case.

Ok, so I have a stereo program inside the DAW that's peaking close to the top of the digital scale (0dBFS). If I keep the faders in the DAW at "0" (and thus the program is truly peaking near 0dBFS), the signal coming out of the DA converters is simply too hot for any analog compressor to handle. I cannot back off on the threshold in the compressor enough to perform gentle limiting. Level going in is just too hot. This makes sense since, in theory, my program must be peaking at like +16dBu or so on the analog side and the compressor wants to see something way less like closer to +4dBu.

One easy fix is to just pull the faders down in the DAW to about -16dBFS... then I won't have any problems with analog compressors following the DA outputs.

BUT.... is there any good reason to NOT pull the digital faders down so much? Somehow is just seems like a bad thing to run audio out with the faders so low (comparatively speaking). But perhaps this is all fine and dandy. Of course in the analog realm it's always been a "no no" to run any output very low, I guess I'm having trouble shaking that mindset.

So just wondering what others have experienced when running outboard analog gear on a pair of DAW outputs spitting out stereo program. Is it perhaps the "norrm" to have to pull your master output faders down to say -16dBFS or so? Or? (I've never heard of this until recently.)

On the other hand, when taking individual tracks out of the DAW when doing analog SUMMING, the individual tracks are rarely peaking near 0dBFS and more likely peaking at -16dBFS so there's pretty much no issue when doing analog summing.

But my question here has to do with specifically taking out a stereo master bus that is already peaking pretty high in the digital realm.

So... is everyone simply pulling their digital faders way down (to like -16dBFS or so)? Is this 100% kosher?

Little by little I'm trying to get a bit more familiar with whole science of levels and how different types of gear interact etc. In one regard, digital is still new to me, at one point someone threw a DAW in front of me and I just started using it before truly understanding all the science.... so just trying to catch up here.

Old 11th February 2013
  #2
teo
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You are probably recording too hot...
Old 11th February 2013
  #3
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This is a good thread to read, the first couple of pages have the info you need.

The Reason Most ITB mixes don’t Sound as good as Analog mixes (restored)

Even if you have recorded hot you can manage the gain staging to get the results you need.
Old 11th February 2013
  #4
Gear Head
 

If you take a screenshot of your mix where we can see you're faders and levels I'm sure someone can help...
Old 11th February 2013
  #5
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Thanks, guys. I will go visit that link soon.

I'd take a screenshot but I'm not able to do that right now.

It's simple though... in this particular case I'm just dealing with 2-track stereo mixes of songs that were previously mixed and bounced with peaks nearing the upper end of the digital scale which is not uncommon these days. Then what I wish to do is play these songs out through my DAW, into some analog gear.

It does make sense to me that if a certain peak is, for example, at 0dBFS, and if the DA converter is calibrated so that -16dBFS = +4dBu, then 0dBFS is going to come out of the converter way hotter than +4dBu, probably above +16dBu or thereabouts... and perhaps this is just too hot for the average analog compressor.

The math all makes sense, it all seems "correct". But, I've just never specifically heard of people having to pull their DAW faders down to say -16dBFS or so when sending out to analog gear.

For whatever it's worth, when I record individual tracks and then send them out individually to be SUMMED in analog, they peak probably barely halfway up the digital scale and thus there is no problems running analog compressors on them.

The "problem" only occurs when I take a 2-track bounced mix that does happen to peak way hotter, up closer to 0dBFS. I was just wondering if this should be considered "normal" or if I am either misunderstanding something or maybe I need to recalibrate my DA converters etc. Again, pulling the DAW faders down to say -16 solves the issue, but I just wanted to make sure that this is considered ok to do.

Thanks, I'll go read that link now....
Old 11th February 2013
  #6
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Quote:
Originally Posted by crosscutred View Post
This is a good thread to read, the first couple of pages have the info you need.

The Reason Most ITB mixes don’t Sound as good as Analog mixes (restored)
Thanks for sending this link. Indeed an excellent bit of information that indeed addresses my concerns.

So, as I take it, in sum, the goal really is to just be careful not to record into digital "too hot" and keep all digital levels far below 0dBFS, or in fact keep them close to the 0VU, 1.23v reference.

By the way, I normally do this, I'm actually not one of those guys looking to pin 0dBFS all the time. I'm in fact very much against that. But recently I happened to have a few master 2-bus digital tracks, stuff I did not mix by the way, and was just messing around and trying to put some analog compression on.

So, I guess, in my case here now, really the only thing I CAN do is simply pull the DAW faders down so that the signal leaving the DAW is indeed closer to the 0VU / 1.23v level... which will mean pulling the digital fader down to, in my case, about -16dBFS (on some systems apparently it would be -20dBFS).

But I do have a question in general, with respect to that helpful post about gain staging... please excuse me if I am misunderstanding...

It would appear that, while recording, the goal is to simply keep your levels / peaks not too far above the 0VU / 1.23v / -16 or -20dBFS reference. If so, then in theory you can just play the tracks out of the DAW with the digital DAW faders all at "0" and all the levels should be good going into your individual analog inputs, like on a console or assorted outboard gear etc.

Though, another option would be to record hotter, record with levels averaging higher than -16dBFS, but then during playback into the analog realm, simply reduce the DAW output faders so that the effective level leaving the DA converters is closer to 0VU / 1.23v.

Is there a sonic penalty of one over the other?

I suppose the only argument here that I could think of is that some folks might say to record to digital as hot as possible for "maximum resolution", then reduce the output level later during playback. But, if I remember correctly, this "max resolution" concept is also something that is often argued about... and I am not claiming to know the answer. I've read interviews with some very well respected producers that have claimed it's best to record to digital as hot as you can (for best resolution), but then I've also read some tech articles stating that this is really not so true, so....?

In the meantime, in my world, most often when I record I go from the mic to the pre then straight into the DAW.... no compression or limiting on the way in. My tracks are always VERY dynamic and it pretty much forces my average input levels to be pretty darned low while trying to "guarantee" not hitting any "overs". From memory, I'm likely averaging around -20dBFS when I record anyway.

I'm gonna go read that gain staging post again, maybe even twice.

Thanks!
Old 11th February 2013
  #7
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Don't over think. If you need to trim the tracks then do it.
Old 11th February 2013
  #8
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Quote:
Originally Posted by rcb4t2 View Post
Don't over think. If you need to trim the tracks then do it.
This, with digital you don't suffer by recording a little lower than you would with analogue, the noise floor is not really an issue once you are past the converters.

Some converters appear to sound worse the closer to their limit you push them, this is probably the analogue part of the circuit running out of headroom. On some it doesn't seem to matter.
Old 11th February 2013
  #9
This is the problem with using different scalse for Digital and analog

If your converters are calibrated that -16dBFS = +4 dBu = 0VU on your compressor, when you're up close to 0dBFS at some peaks then you are at some points hitting your converter with +20 dBu. That's 7.75v into a piece of gear expecting a line level input at around 1.23v. Not sure what bus comp you're using but mine has a maximum input of +20dBu and doesn't sound good being hit that hard.

I don't believe there is any problem in pulling the DAW master faders down a little if the mix is already done and finished up that hot. I'd imagine any miniscule "damage" to the audio due to this is going to be far, far, far less significant than pinning the meters on an analog comp throughout the entire mix, unless of course you are looking to add a lot of distortion and an enormous amount of compression
Old 11th February 2013
  #10
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Quote:
Originally Posted by Bristol Posse View Post

...If your converters are calibrated that -16dBFS = +4 dBu = 0VU on your compressor, when you're up close to 0dBFS at some peaks then you are at some points hitting your converter with +20 dBu. That's 7.75v into a piece of gear expecting a line level input at around 1.23v. Not sure what bus comp you're using but mine has a maximum input of +20dBu and doesn't sound good being hit that hard.....
I've tried assorted different bus comps, GML, SSL, etc, they all behave the same way. The issue is, the level of the audio going into them is so hot that the compressors instantly go into severe gain reduction, even with the threshold knobs backed all the way "down" or "off". It's impossible to do mild compression. Of course one cannot work this way.

If I reduce the output faders in the DAW, then I can get it all working ok... but I'm finding that I need to reduce the faders considerably... this makes sense, at least after reading all the above etc. We can't have 7+ volts coming out, needs to be closer to 1.23volts... and this requires dropping the fader possibly as much as -16dBFS... or in some cases maybe not even that much, but I'm finding that I need to drop the fader at least -6dBFS if not -10dBFS to keep the highest peaks completely out of threshold when the threshold controls are fully reduced. But, if doing this is ok, then fine.

Finally, this all makes sense and isn't rocket science.... but it surely is something that every engineer needs to know. Yeah, too bad that DAW meters etc are not marked, calibrated or "limited" in such a way to keep folks from accidentally making serious gain staging errors when interfacing with analog. I'm personally very much not into the "chaos" with all this level business. But, it is what it is, we just need to learn how to properly handle it. This is a valuable lesson for all.



EDIT: here's an idea.... maybe someone already makes it... a software plug-in for DAWs that gives you a dedicated channel output VU meter and/or dBu meter and/or even a volt meter, per channel... though, I guess this is tricky when applying universally since it seems many DA converters are calibrated differently.... but I suppose the software could require you to calibrate and test your outputs first and get it all synced up before using. I'd buy it!
Old 11th February 2013
  #11
Quote:
Originally Posted by 666666 View Post
EDIT: here's an idea.... maybe someone already makes it... a software plug-in for DAWs that gives you a dedicated channel output VU meter and/or dBu meter and/or even a volt meter, per channel... though, I guess this is tricky when applying universally since it seems many DA converters are calibrated differently.... but I suppose the software could require you to calibrate and test your outputs first and get it all synced up before using. I'd buy it!
A calibrated test tone and a good RMS voltmeter are really all you need and you only need to test your gear once to know where everything sits.

this Site can be really useful too

I use REAPER as a DAW and the master meters can be calibrated to show you where 0VU is based on how your converters are calibrated. It's a nice touch and would be good to have on the track meters too for those of us using with hardware, but beggars can't be choosers I guess
Old 11th February 2013
  #12
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You could always just lower the output cal of the converter... -14 = +4 dBu (+18 dBu max) is pretty common. You are on the right track though to be thinking of all this, nice job!
Old 11th February 2013
  #13
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If you use Protools, run your master buss insert on the master fader. You can just pull down the master fader to get the level where you need it. The fader on the master bus is pre-insert.
Old 12th February 2013
  #14
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OP: What you're experiencing is normal and expected behavior when playing a hot mix out of your converters into a pro (+4dBu) analog piece of gear. Pulling the master fader down is one way to deal with it, and put the levels back in the operating range of your compressor (other options are a trim plugin, or perhaps removing any plugs on your master that may be increasing gain).

The reality is that when interfacing analog gear with the digital world, in order to keep your analog gear (including your pres on the front end!) operating in the range they were designed to you'll need to keep your average levels in the digital world hanging out around -18dBFS. That means that (in Pro Tools, for example) your meters won't look very hot at all. But at 24 bits most seem to agree that any kind of resolution loss is very small and inconsequential.

The reason that this type of problem gets largely overlooked while recording is that most good quality analog gear has so much headroom that it'll operate significantly above the nominal +4dBu level without producing noticeable distortion. For example, you can run an API 512 hot enough so that you're almost clipping the converter, without hearing any "problems". There are a few cases where you will hear trouble though. For example, probably one of the most popular vocal chains right now involves a 1073 pre into a CL1B compressor. The input stage of that compressor is on the sensitive side, and if you push the pre too hot in front of it you'll notice distortion from it long before you're clipping your converter.

A good rule of thumb is that unless you're printing a mix (which needs to be hot enough for your client to reference against commercial releases), keep your levels into the converter, within the DAW, and out of the converter averaging around -18dBFS (assuming your converters are calibrated to -18dBFS=+4dBu). Keep in mind that I said "averaging", as in an actual average level such as RMS. Since DAW meters tend to be peak meters, that means your peaks will still be higher than -18 obviously. (The relationship between your peak and average levels will vary based on program content.) In most cases that means that your peak levels shown on the DAW meters will stay well below 0, and probably below -6dBFS.

In your specific case, the simplest way for you to get useable level into your compressor is to put the meter on the compressor into the "input" mode (assuming it'll do it) and adjust your converter outputs with the master fader etc. until you're in the neighborhood of 0VU'ish shown on the compressor input.
Old 12th February 2013
  #15
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Quote:
Originally Posted by Bristol Posse View Post
I use REAPER as a DAW and the master meters can be calibrated to show you where 0VU is based on how your converters are calibrated. It's a nice touch and would be good to have on the track meters too for those of us using with hardware, but beggars can't be choosers I guess
I think this should be a standard feature on every DAW. It would certainly help clear up some of the confusion that seems to come up frequently on this subject.
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