2. digital
  3. 1373371136

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

Showing 6 responses by audioengr

audioengr
3,282 posts
 
The fact is that no preamp will most of the time be better than using an active preamp. A transformer-based linestage (TVC) is one option. A DAC with really good volume technology (not like an active preamp) is another option. Both of these require that the DAC have a strong output buffer. Op-amps need not apply.

The best overall solution IME is to use a combination of volume control with a TVC or; DAC (with exceptional volume control technology) or discrete gain settings and a limited amount of digital volume control The ideal thing is to use up to -10dB of digital volume decrease and no more than that. This way the digital part can be the remote controlled part and the fixed volume can be manual.

So, there are these requirements:
1) sufficient drive from the DAC
2) Passive TVC or
3) DAC with discrete gain control or
4) DAC with reference voltage volume control

Steve N.
Empirical Audio
audioengr
3,282 posts
 
Like I said, the output of the DAC must be low-impedance with a lot of drive capability and then no preamp can beat it.

It just makes engineering sense. The more stages you add, the more noise, compression and distortion gets added. Less is more. If the output stage of the DAC is as good as any uber-expensive preamp (including power delivery), it will beat it.

Steve N.
Empirical Audio
audioengr
3,282 posts
 
Ed - 99.9% of iPod users use the stock earphones too. Means nothing. Means that they are just uninformed.

Steve N.
Empirical Audio
audioengr
3,282 posts
 
Oferi - The input impedance of an amp has nothing to do with the dynamic response to an input current and voltage signal. It's usually only a resistor to ground.

Just put a resistive passive linestage to an amp and you will typically experience a loss in dynamics.

Steve N.
Empirical Audio
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
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
More to discover