Digital Volume Control - understanding how it works.

[Dr X]

Serious question actually. JRiver claim their digital volume control to be be "perfect" and have some mathematical proof for it. Just wish I could find the damn link!

[andreasmaaan]

Serious question actually. JRiver claim their digital volume control to be be "perfect" and have some mathematical proof for it. Just wish I could find the damn link!

I do recall stumbling across that link at one point, think it might be on their wiki page?

My ears certainly don't agree though. I could perhaps be more specific by adding that by "sounds better" I meant sounds closer to the unattenuated signal - to my ears of course!

[Nada]

"All audio handling inside the program is done with 64 bits of precision....... As a result, should you choose to use them, digital volume, room correction, and other audio functions are pristine."

Theres a difference between perfect and pristine.

Edited August 3, 2012 by Nada

[Dr X]

Ah good Nada, that link has their program proof that their 64 bit internal digital volume control is "perfect".

Subjectively it sounds perfect to my ears too, but of course I'm biased

[Addicted to music]

If its perfect and prestine to your ears, it'll be idea for mine

Edited August 3, 2012 by pchan

[davewantsmoore]

Sure, their proof is fine.

... but it does not cover the issues raised in the OP.

Generalising about analog vs digital volume is difficult. There's always an exception to the rule.

[Dr X]

... but it does not cover the issues raised in the OP.

And those issues (plural) are?

Edit: Main question is...in a really good day modern system...did anything Sean Adams say there have any audible effect at realistic listening levels?

If I set my digital volume control to 0% (-96db) am I expected to hear noise out of my speakers coming from the DAC(s)?

Edited August 3, 2012 by Dr X

[davewantsmoore]

And those issues (plural) are?

Sorry, I didn't mean to plural.....

That digitally reducing the level coming out of a DAC only reduces the level of the signal, not the noise.

Edit: Main question is...in a really good day modern system...did anything Sean Adams say there have any audible effect at realistic listening levels?

This depends on how much attenuation you are using and how noisy your DAC is.... and how much dynamic range you desire (can hear).

If I set my digital volume control to 0% (-96db) am I expected to hear noise out of my speakers coming from the DAC(s)?

Maybe, depending on the above.

Like I said, you really don't want me to generalise. The answer is always that it depends. Anyways, there are other issues a million times more important in playback.

The mistake is people trying to have a debate and "settle which one is best/flawed/whatever". It is just another potential pitfall in system design, that is all.

[ehtcom]

Reduced signal to noise ratio at low volume.

[Monkeyboi]

So what ESS is say is no secret, digital volume is popular because of the destructive nature of normal volume potentiometers, and that includes all of them regardless of make and material used.

Hmmmm..... this sentence almost reads as though potentiometers or devices that contain them need to accompanied with a safety warning.

"Good evening Mr. Phelps. This amplifier with an analogue volume control will self destruct after 200 rotations of the volume control knob. The manufacturer will deny any knowledge of their inaction to prevent this. Should you be harmed in any way it's your bloody fault - LOL."

Cheers,

Alan R.

Edited August 3, 2012 by Monkeyboi

[Dr X]

The mistake is people trying to have a debate and "settle which one is best/flawed/whatever". It is just another potential pitfall in system design, that is all.

Fair enough Dave, it does come down to what's best for each individual already existing system.

But having said that, we could have a debate of what's best if one was attempting to assemble "the best possible" system, from the ground up.

If we did, IMO digital volume control would be part of it, especially something like what's been implemented in JRiver's 64 bit internal.

[Monkeyboi]

From my experience I have always wanted to to use a intergrated volume chip like the WM 8816 or a step resistor relay control. Its the 1st I have heard of mercury switching jkeny and Im glad that you have mentioned it, as you can see the innovation is great to see but, mercury is not a very good conductor as: http://environmental...electrical.html as you can see from this table. So the benefits of using mercury defeats this purpose.

Mercury wetted contacts (albeit now not favoured for enviornmental and cost reasons) are well suited to circuits with low voltages and currents, for example audio signal levels. The mercury prevents oxidation of the contacts and actually maintains a good low contact resistance over time compared to contacts exposed to air and humidity. It was used extensively in low voltage / low signal level telecommunications equipment until it was deemed too costly and hazardous so many relay manufacturers discontinued its use.

Cheers,

Alan R.

[Arg]

Reduced signal to noise ratio at low volume.

Same as analogue, as far as everything downstream of the pot is concerned. [edit: spelling]

Edited August 3, 2012 by Arg

[andreasmaaan]

The mistake is people trying to have a debate and "settle which one is best/flawed/whatever". It is just another potential pitfall in system design, that is all.

+1

[andreasmaaan]

Ah good Nada, that link has their program proof that their 64 bit internal digital volume control is "perfect".

Subjectively it sounds perfect to my ears too, but of course I'm biased

I'm now very curious to hear whether anyone else has done the M51 vs Jriver comparison??

To my ears there was a very significant difference.

Dr X, i do admit that I'm using the jriver attenuator now anyway because my preferred DAC doesn't have an attenuator, which I suppose proves it can't be all that bad....

[davewantsmoore]

But having said that, we could have a debate of what's best if one was attempting to assemble "the best possible" system, from the ground up.

If we did, IMO digital volume control would be part of it, especially something like what's been implemented in JRiver's 64 bit internal.

We could ... although "best possible", is just about minimising compromises.

You should feed a DAC chip with a full scale signal to extract it's best performance. The fact that you would choose to attenuate the digital level entering the DAC using high precision maths does not alter this recommendation.

Altering the volume level inside the DAC chip (not before it), is maybe a different matter, as it is implementation dependant.

As far as I am aware, jRiver do not recommend using their software volume if your audio hardware (eg DAC) has it's own volume control. The assumption there (and it is an assumption) could be that doing digital volume inside the DAC chip (or some analog volume control after the DAC) is more superior.

[Addicted to music]

Mercury wetted contacts (albeit now not favoured for enviornmental and cost reasons) are well suited to circuits with low voltages and currents, for example audio signal levels. The mercury prevents oxidation of the contacts and actually maintains a good low contact resistance over time compared to contacts exposed to air and humidity. It was used extensively in low voltage / low signal level telecommunications equipment until it was deemed too costly and hazardous so many relay manufacturers discontinued its use.

Cheers,

Alan R.

Thats way before my time Alan,

so what youre saying is that electrons flow better in a liquid form than on solid state such as copper or silver??? :P LOL Wonder if they get dissy finding there way to gnd

[Addicted to music]

And those issues (plural) are?

Edit: Main question is...in a really good day modern system...did anything Sean Adams say there have any audible effect at realistic listening levels?

If I set my digital volume control to 0% (-96db) am I expected to hear noise out of my speakers coming from the DAC(s)?

If you set to zero db or no attenuation than that is the setting where there is minimum distortion and zero digital errors, its when you listen to low level/ maximun attenuation that distortion is huge. Look at the M51 review.

[davewantsmoore]

Same as analogue, as far as everything downstream of the pot is concerned. [edit: spelling]

Not really.

Reducing volume digitally reduces the signal but not the noise coming out of the DA converter. Reducing analog level reduces both. Yes, an analog circuit degrades SNR, but this is (very likely to be) constant at all levels.

Note, I'm not saying that one is always going to be superior to another. (As you've noted,) with appropriate gain in a system, you would ideally not be using very high levels of digital attenuation.

[Dr X]

If you set to zero db or no attenuation than that is the setting where there is minimum distortion and zero digital errors, its when you listen to low level/ maximun attenuation that distortion is huge. Look at the M51 review.

I didn't say 0db.

I actually said 0% which is -96db in JRiver MC, so my question remains.

[Dr X]

As far as I am aware, jRiver do not recommend using their software volume if your audio hardware (eg DAC) has it's own volume control. The assumption there (and it is an assumption) could be that doing digital volume inside the DAC chip (or some analog volume control after the DAC) is more superior.

I don't believe they (JRiver) recommend that at all. Where did you get that from?

[jkeny]

Thats way before my time Alan,

Then you should listen to the voice of experience

so what youre saying is that electrons flow better in a liquid form than on solid state such as copper or silver??? :P LOL Wonder if they get dissy finding there way to gnd

Again, listen to what Alan, says - mercury wetted switches were known to sound better because they avoided oxidation of the contact points in a switch or attenuator. The oxidated layer of copper is a worse conductor than the mercury, hence the explanation.

[Addicted to music]

Then you should listen to the voice of experience

Again, listen to what Alan, says - mercury wetted switches were known to sound better because they avoided oxidation of the contact points in a switch or attenuator. The oxidated layer of copper is a worse conductor than the mercury, hence the explanation.

I am listening and learning like i said, it was an innavative way in devising a switch or a switching contact, this is the 1st I have heard of it. I dont think that mercury is used now due practicality and to its toxicity to the environment. If you are aware of a manufacturer using murcury switching let us know!

You wouldnt use copper or silver to act as a switching contact points, like you said these metals are highly corrosive when exposed to the natural environment apart from gold, switching contact and relays are made with more stable alloys, but as an alloy (combining 2 or more metals) naturally lowers conductivity. This is why typical mechanical volume controls are not a good idea to be placed in an amplifer, every material changes the SQ and colors it, not to mentioned the wear and tear factor that occurs over time. Like I mentioned in previous post that some amplifier manufacturers in the late 90-2006 are using volume controls that attenuate in the analog domain, without traditional pots, but these are expensive implementation, Silicon Chip had an artical that did this but the chip they used was no longer manufactured, it was expensive and the whole project would have set you back $500AUS plus. So when DAC engineers place volume control in there packages it was a cheap way to implement but at the cost of bit reduction.

[Arg]

Same as analogue, as far as everything downstream of the pot is concerned. [edit: spelling]

Not really.... an analog circuit degrades SNR, but this is (very likely to be) constant at all levels.

Hi, only upstream of the pot.

Downstream of the pot, let's say you have a valve amp (pre, power, whatever) which has 60dB SNR at full power (maximum signal). Turn the pot down by, say 12 dB and you now have 60-12=48 dB of SNR.

Exacty the same thing happens with a digital pot, as far as everything downstream of the pot is concerned. The so-called resolution loss of digital is at the same rate, turn it down 12dB and resolution falls by 2 bits which is 12dB of SNR reduction.

[jkeny]

Don't think there is anyone doing mercury wetted switches now but I may be wrong.

Another way to avoid contacts in an analogue volume control is to use Light Dependent Resistors (LDR) - there are units that have a LED & LDR combined in one device so varyng the current to the LED varies the resistance of the LDR & thereby the volume.

Look up Lightspeed Attenuator! There's also some threads on DIYAudio about DIY versions . Actually Greg Ball of SKA Audio sells some kits called OptiVol very cheaply!

Edited August 4, 2012 by jkeny