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Optimizing Digital Volume Control

Hi,

First I would like to state that I am relatively new to audiophilia (sounds like a disease), however I have a relatively good engineering background.

Presently I am using a traditional CD->DAC->pre->power->speakers setup. I am using a Hegel HD20 DAC that has a digital volume control feature. I recently noticed that without the pre (ARC LS2) in the chain, using the DAC for volume control, I get better results.

Since the DAC is 24b, having a -140db noise floor (close to 144db theoretical limit) this makes sense to me. Since a CD, having 16bit resolution, supports a theoretical maximum of 96db (practical implementation are below 90db). So s properly designed digital attenuation of over 50db (probably in this case over 60db) should not degrade the sound.

Now to my question, assuming a computer as the source, followed by a 24b DAC that doesn't support volume control, one can in theory achieve the same results if the computer converts the 16b original data to 24b and then apply digital volume control. In this case the computer should output a 24b signal to the DAC.

Does anyone know if this is something that a JRiver or Foobar solution is capable of doing? or in general, does anyone know how volume control would work using JRiver or Foobar?

Thank you in advance for your attention.
oferi
oferi OP
12 posts
 
Audioengr, I agree that the input impedance of a power amp is probably slightly frequency dependent, and hopefully not amplitude dependent. So I agree that a low impedance source is a good idea. My point is only in regards to how low is good enough. A 200 ohm source into a typical amp would be plenty good (as evident by the design of reference preamps having a 200 ohm or bigger series resistor at the output). On the other hand a passive (pot) would probably degrade the quality if its impedance is on the order of the amp input impedance.

BTW, a passive volume control with a 20K ohm into a 100K good amp seems to do an excellent job (but not as good as the best preamps).
zd542
5,339 posts
 
"07-10-13: Edorr
Steve, this is the theory. As I mentioned, nine out of ten of the guys on whatsbestforum with six figure systems end up adding a preamp to their DAC. They can't be all tone deaf and/or suckers. As Denon mentioned, you need to spend $20K (and up) to get the desired result, which they do."

I agree overall, but you don't have to spend 20k. If you match your components well, you can get away for less.

You can also get great sound without a preamp. In both cases, it comes down to good system matching and what you like.

Oferi,

For someone with 6 months experience in audio, you seem to have your mind made up about a lot of things. Nothing wrong with that. I won't tell you how to think. You did ask for advice, though. You appear to have a good start on the technical aspects of audio. I would now balance that with some listening experience. Not everything in audio can be measured. If you don't accept that and find a way to blend your listening experience with the tech aspect, this will not be a fun hobby for you.
audioengr
3,282 posts
 
Oferi - I have had he opportunity to compare good active preamps with passive resisive, passive transformer and DACs with good drive. Comparing some of the best of each I conclude that resistive passive is the worst. Transformer and a good DAC are the best.

Output impedance in the 20 ohm range is much too high. Needs to be in the 10 ohm range. Has nothing to do with the terminating resistor in the amp.

Steve N.
Empirical Audio
audiolabyrinth's avatar
audiolabyrinth
4,555 posts
 
@ Audioengr , You mean above 200 ohms on the digital source is to high and 100 ohms is Ideal!, I agree!, cheers.
audioengr
3,282 posts
 
Even 100 ohms is too high IMO. The lower the better. This alone does not guarantee that the output driver is a good one though. It also requires good circuit design and parts choices as well as good power delivery infrastructure.

Steve N.
Empirical Audio
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