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Questions about compressors and audio conversion quality


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Can a compressor aid the digital conversion process to become more pristine? My setup is very simple (at least so far). I go through an analog mixer and from there to an audio interface that does AD conversion and that's it. So the AD conversion is really a big part of my final sound. I record in 24-bit and dither to 16-bit from there. The mixer is built with premium grade mic pre amps (don't know if it's true though :) What I mean is, can I win signal-to-noise by using high quality compressors only expanding and limiting a little and by using gate before the audio conversion, or is this just in rare cases when for instance the singer would move away from the mic pretty much at random or some distortion guitar would have much idle noise? I don't mean by making the conversion more "natural sounding" and less transparent, I just mean getting better final sound quality from the A/D conversion. (when not thinking about compressors as gates and limiters for removing outside noise) If in fact compressors are useful for this, how do I configure the compressors for this purpose to achieve the best result (generally without removing too much dynamic range)? Is the result dependent on the kind of instrument recorded? Does it make a difference if the compressor is added before or after the AD if a compressor probably will be used on that channel?

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While some comression on the way in can increase the dynamic range of the signal, there are some factors to consider, the biggest one being you are then stuck with that compression, you've recorded it and there is no undo, except to retrack.

 

With 24 bit depth, theres not need to pin the input, target your nominal level to the 0dbu reference of your particular converters, you'll have optimum autio quality and plenty of headroom for transient peaks without overshooting.

 

AFA improving the quality of your ADDA with compression, no you will not. You'd need to get better converters to do that. The quality of your recordings is highly dependant on the quality of the converters, and IMHO they are amongst the most important parts of the chain. All the best gear is worthless if you have second rate converters, and that goes for the DA as well as the DA. If you can't hear what your mixing your mixes will never be accurate.

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A compressor changes the dynamic envelope of sounds, and usually adds some color. So if your definition of "pristine" means transparent and colorless, a compressor definately is the wrong thing.

 

It can be tempting to think that a compressor can help solve your gainstaging problems when tracking. Obviously you don't want to track too hot (clipping) or too low (poor signal to noise). A compressor controls dynamics (effectively lowers hot signals and raised low signals) - so it can be tempting to think that this will solve your problems.

 

I believe this thinking is wrong - very wrong - for these reasons:

 

1 - for clean transparent tracking, the shortest path is best. Every additional cable, connector and amp stage adds voltage drop or noise, so the shorter the path the better.

2 - it's the transients that clip digital. A compressor let's the transient through! Even if you set it as fast as possible (noticeably destroying your sound), the very first transients will still slip through and clip your A/D. You achieve nothing except damaging your sound.

3 - more controls are now necessary to set up your gain-staging correctly. If you had trouble setting your preamp before, you will now have the compressor input gain and output level to worry yourself about.

4 - you are committed to the sound - it's destructive, and you can't really undo if you over-compress. Tracking without gives you more options at a later stage.

 

I believe it made much more sense to use a compressor in the days of magnetic tape - because tape absorbed transients, so you were mainly concerned about average level to tape (not peak level, which is so critical for digital). We have plugin compressors now, and generally don't have the noise problems of tape, so getting loud levels isn't such a problem with digital.

 

Some people may disagree, and say it's good to track with compression. If you love the sound of a particular compressor, and know exactly what you are doing, that's great. There are benefits if you know what you are doing. But there a big traps if you aren't sure. If you have to ask, don't do it.

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