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digital volume attenuation vs analog
Old 7th September 2013
  #1
Here for the gear
 

digital volume attenuation vs analog

What's the story on digital monitor out attenuation that occurs either from the knob on your audio interface or the fader in your audio interface's software mixer? Does it decrease bit resolution and therefore decrease headroom and degrade the signal going to your speakers?

Does this mean that if you usually monitor at a moderate level, attenuated digitally by your interface, are you constantly working with a fraction of the possible bit resolution that you could be?

If there's a thread where this info exists, by all means, point me there!
Old 7th September 2013
  #2
Gear Maniac
 

Yeah there is degradation. It's mostly neglible tho. A little bit more detailed here (read what rme writes about it) https://www.gearslutz.com/board/9394891-post7.html
Old 7th September 2013
  #3
Quote:
Originally Posted by nept View Post
Yeah there is degradation. It's mostly neglible tho. A little bit more detailed here (read what rme writes about it) https://www.gearslutz.com/board/9394891-post7.html
Attenuating from within the digital realm does raise the noise floor by the amount you attenuate. With a 24 bit DAC, moderate attenuation shouldn't be much problem. But if you start looking at 50 or more dB of attenuation from the theoretical 140 dB signal-to-noise ratio permitted by 24 bit, that lowers the effective signal-to-noise ratio down to around 90 dB. That's roughly the practical SNR of a CD -- still very good, but maybe a reasonable threshold to begin being concerned.

The signal is being 'degraded' in the sense that the noise floor is raised, but it's not like the above-noise-floor signal is mangled. And, at that 'reasonable threshold of concern' of 90 dB, the noise floor would be as good as silent scaled against normal program level signals.

All that said, if you have really loud speakers (and I have a pair of 200w/ch powered monitors that I fell in love but which are easily twice as loud as I ever would have needed and maybe three times as loud as I need now (since I no longer have a sound-proofed studio) and they don't have a huge amount of built-in attenuation (mine have, I think 20 dB from screwdriver pots in the back), you may end up having to turn down from the digital side a fair amount.

However, with less powerful monitors (or higher working levels), it may not be much of an issue at all. You can frequently put your mind somewhat at ease by doing the math, seeing how much attenuation you're dialing in from the digital side and subtracting that from the theoretical 24 bit SNR of 140 dB. If it's below 80 dB all the time (ie, 60 dB of attenuation, that's a lot), maybe it's time to think about an alternate form of attenuation.


But don't forget, analog attenuation has its own gotchya's, too. If it's active, there will be *some* potential increase in noise (probably little and probably insignificant with a quality unit); if it's a passive control, it will change the impedance as the level changes and that will change tonal balances slightly. The greater the attenuation, the greater the shift as a rule of thumb. Either way, making two analog potentiometers with very, very similar tapers -- to avoid wavering center image as you turn down the ganged pots -- can be very expensive in today's manufacturing world. When every home had 10, 20, 30 rotary potentiometers scattered through it, the economies of scale meant you could buy them fairly reasonably (even if you, yourself, were not buying 50 thousand). But today, pots are not nearly as common in gear (particularly outside our realm) and so any quality, stereo control is going to be on the pricey side.
Old 7th September 2013
  #4
Gear Maniac
 

Great summary on the practical implications theblue1. I don't think there's many systems needing a 50 db reduction. Assuming they naturally play at brutal 120db spls, at -50dbs they're down to 70db spl which is really rather quiet (and then the 90dB SNR is 20dBs too much to hear the noise... ^^). Anyway it left me wondering weather we really can't tell appart an 8bit from a 16bit file @ 40db spl. Since the SNR @ 8bit is ~-48db's we shoulnd't be able to. I just cant imagine not being able to tell em appart, no matter what volme hey're played at. Wished I had a dB meter here to test it.
Old 7th September 2013
  #5
Lives for gear
 
DCtoDaylight's Avatar
 

Quote:
Originally Posted by theblue1
Either way, making two analog potentiometers with very, very similar tapers -- to avoid wavering center image as you turn down the ganged pots -- can be very expensive in today's manufacturing world. When every home had 10, 20, 30 rotary potentiometers scattered through it, the economies of scale meant you could buy them fairly reasonably (even if you, yourself, were not buying 50 thousand). But today, pots are not nearly as common in gear (particularly outside our realm) and so any quality, stereo control is going to be on the pricey side.
Huh - I'd never thought of that angle before, but you're quite right! Another place where analog is shuffling off to Buffalo. Maybe someday people will have whole discussion threads about tracking down NOS stereo pots...

Also, good explanation of the issues on the OP's question.
Old 7th September 2013
  #6
Quote:
Originally Posted by DCtoDaylight View Post
Huh - I'd never thought of that angle before, but you're quite right! Another place where analog is shuffling off to Buffalo. Maybe someday people will have whole discussion threads about tracking down NOS stereo pots...

Also, good explanation of the issues on the OP's question.
I hope so.

To be honest, it's so stinkin' hot and stupid humid here that it feels like someone swapped my brain for a big sponge filled with hot dishwater...


PS... circling back around to consumer devices... pursuing this line of thinking a while back (comparative digital and analog noise floors, etc) a while back DID make me wonder how many consumer devices (stereos, tabletops, portables, phones, tablets, etc) use better than 16 bit for media processing (like in volume control) and output.

We may not have too much to worry about with our 24 bit headroom -- but I've noticed my consumer devices can seem even more crappy sounding when you turn the volume down on the unit but turn the input up on a sound system it's plugged into (intentionally bit-starving it, if you will).

Still, I extended that 'bit-starving' experiment and did some informal (non ABX) tests on my MOTU, reducing the gain by, like 72 dB... it didn't sound horrible at all. But I couldn't shake the sense that it didn't sound as good. And, you know, that would certainly be believable on the numbers -- though, when I was a kid (by cracky), a home stereo with a 65 dB SNR was considered quite decent. (It's a bit tricky comparing the digital noise floor with its analog counterpart, of course. I'm no digital engineer (more like failed college poet) so I'll just shut up now. )
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