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Volume control with computer & DAC


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Hi all,

 

There is something that is nagging me about volume control that I hope someone would be able to share their knowledge about.

 

Let's say I have a Computer->DAC->Amplifier->speakers set-up.

 

If my pc has a S/PDIF output, and I use that interface to connect to the DAC, then volume is implemented directly within the PC. Sample values are digitally reduced then sent to the DAC.

 

However, using a USB DAC muddies the situation a little. It is conceivable that the PC is sending the original, full-valued samples over to the DAC, and then the DAC is performing volume control during the D/A conversion.

 

Would anyone be able to provide me with any insight as to what is going on and how it can effect sonic performance?

 

Thanks!

 

Bryston BDP-3 > Bryston BDA-3 > Levinson 526 > Levinson 532 > Revel Salon2

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Thanks for the response.

 

My DAC in the above system is theoretical at this point.

 

I don't see why one could not design a USB based DAC with PC driver software that implemented volume control within the DAC itself, as a function of the D/A process itself, no hardware volume knobs needed. Unlike the S/PDIF, all sorts of command instructions can be passed, along with music samples, across the USB link.

 

In theory, such an implementation could have very real sonic advantages. So I doubt I am the first person to have this idea ;)

 

Bryston BDP-3 > Bryston BDA-3 > Levinson 526 > Levinson 532 > Revel Salon2

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I don't see why one could not design a USB based DAC with PC driver software that implemented volume control within the DAC itself, as a function of the D/A process itself, no hardware volume knobs needed.

 

Of course, even the cheapest USB sound cards offer volume control via USB, using standard usb audio specifications. Vast majority of them control volume in digital domain, in the actual DAC. But it is only about implementation, the communication protocol is standardized and should be supported by stock usb drivers.

 

SPDIF has no standardized control channel, unless some parts of the spdif frame header were "misused" which would make the solution proprietary.

 

 

 

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Paul,

You can either control volume in the digital or analog domain. In the digital domain, this can be done either by the music playing software - such as iTunes - or at the DAC itself, what happens is that you are throw away bits (ie resolution), so my humble understanding is that there would no sonic advantage to do it either start or end of the chain. Try searching here on the forum as there were lengthy discussions about this.

 

If you meant a digitally controlled analog volume at the DAC, then you need specially designed software or driver for that particular DAC. So it probably can be done but am not aware of any example.

 

In my personal opinion, the volume control of your ML 326s should be superior to any built-in volume control in any DACs known to man.

 

Mac Mini ? Weiss DAC202 ? ML 326s ? ML 532h ? Wilson Sophia3

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The Wavelength Proton has an analogue volume controlled via the volume control setting of the computer .. Is this what you were asking for?

 

Eloise

---

...in my opinion / experience...

While I agree "Everything may matter" working out what actually affects the sound is a trickier thing.

And I agree "Trust your ears" but equally don't allow them to fool you - trust them with a bit of skepticism.

keep your mind open... But mind your brain doesn't fall out.

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Are you asking for digital attenuation within the DAC as opposed to analog attenuation within a DAC? If so, the Sabre DAC chip will do that, and I am sure other DACs besides my DIY one will use that function.

 

Forrest:

Win10 i9 9900KS/GTX1060 HQPlayer4>Win10 NAA

DSD>Pavel's DSC2.6>Bent Audio TAP>

Parasound JC1>"Naked" Quad ESL63/Tannoy PS350B subs<100Hz

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If you meant a digitally controlled analog volume at the DAC, then you need specially designed software or driver for that particular DAC. So it probably can be done but am not aware of any example.

 

Please see my post right above yours, the concept of control elements is built into the usb-audio standard. How the commands are implemented in the actual USB device is up to its designers. Instead of communicating with the actual DAC chip and control its digital volume feature via I2C they can opt for relais voltage dividers. But it definitely takes more effort and expenses :-)

 

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A nice example of controlling external devices via standardized API is arcam-av plugin for linux alsa http://git.alsa-project.org/?p=alsa-plugins.git;a=blob_plain;f=doc/README-arcam-av;hb=HEAD . This plugin defines new audio controls exposed to all alsa-aware applications which directly manipulate the Arcam AV functions via RS232

 

http://git.alsa-project.org/?p=alsa-plugins.git;a=blob;f=arcam-av/ctl_arcam_av.c;h=0ab14605bf30482e395629284ec66b5e2d21776a;hb=HEAD#l39

 

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Thanks for all the input, guys.

 

So this has been some very interesting news to me.

 

Apparently there exists as least one USB DAC in which volume control is done in the analog domain, and controlled by the OS's main volume control? (Wavelength Proton)

 

As also mentioned above, this method, in theory, has sonic advantages over both a DAC connected to a PC via S/PDIF, and a USB connected DAC that implements its volume control in the digital domain.

 

So the question is: How does one tell if their USB DAC is doing volume control in the digital or analog domain? Not exactly something I see when I look at the specs ;)

 

 

Bryston BDP-3 > Bryston BDA-3 > Levinson 526 > Levinson 532 > Revel Salon2

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