Software mixer VS Audio Quality Question

I am trying to understand the statement that using the “Software Mixer” reduces audio quality. I have completed both MIT’s Graduate course in Digital Signal Processing and MIT’s Undergraduate course in Acoustics. It is my understanding that integer multiplication has been working reliably in computers for decades and its application to gain control of digitized audio signals is well understood. So…

  • Am I missing some sort of latency related problem that is not present when the bits go straight through without an intervening multiply?
  • Is it that the signal error at the Least Significant Bit level due to truncation of the multiplication result is detectable to (at least some) Volumio users’ ears?

The aversion to a Software Mixer feels like a purist issue rather than a practical issue to me, but I admit that I could have easily missed something. I would appreciate being corrected if my thinking is flawed. I’m currently using the Fiio K5’s and my stereo pre-amp’s front panel knob volume controls for now, but I am tempted to achieve remote control by enabling the Software Mixer.

Primary Volumio Setup: RPi4 → Fiio K5 → McIntosh (solid state) → Klipschorns
Secondary Volumio Setup: RPi3 → Innomaker HiFi DAC Hat → Proton 300/301 bi-amplified bookshelf system (occasionally substitute Sony SRS-150 powered bookshelf speakers)

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Because it is, there are million more important things for SQ than this, and most systems are limited by these other things.

Besides most “hardware mixers” in DAC boards does the volume control in the digital domain, which is same as using software control.


In short.
Modifying volume level in the digital stage, can be noticeable at the analog end (speakers).
This is not caused by the actual audio signal, but due to the noise level. The processed original audio signal can be lowered, however the noise remains on the same level. (The SNR will get worse).
Please have a look here, it’s pretty well documented and easy to read/understand.

How to test

If you have a pre-amp or a DAC with analog volume control, you can simply test the impact of both digital and analog volume control.
Set the digital volume control of your media player (volumio) to 100%, hopefully this is 0 dBFS.
Play at a realistic level. Turn down the digital volume (Volumio) and increase the analog (Pre-amp) at the same time trying to keep the level constant.



Give in to that temptation.
If you can actually tell any difference with real ears, you can always resist the temptation in the light of experience. If anyone complains that you’ve ruined the fidelity, force them to go through a punishing series of blind AB trials until they cease complaining.

I think the statement is a sort of defence for the (no doubt correct) claim that Volumio is as far as possible reproducing sound in bit perfect style, against the theoretically valid objection that a software mixer can affect the SNR.

I think you would struggle to concoct a real music system in which this is a genuine problem. So in practical terms, though we are all scientific rationalists here, in this case I would go with your instinct to use svc if you find it convenient. There are worse ways to control volume.

The ultimate solution:

No volume control on Volumio, volume control on a LAN hooked amplifier.

That’s how I use it. Both, Volumio and the amplifier are controlled by a Smart home center, in my case Home Assistant, so they are together in one app :wink:

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How does the amplifier attenuate the volume?
poti …

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I get that and also get that this is not unique to digital. E.g. arithmetic overflow in an IIR or FIR filter is not-unlike overloading an analog output or input stage.
My default in the analog world is to set all cascaded level controls to roughly same percentage of full scale. typically this means I’m unlikely to suffer either overload or low SNR. Of course I make an exception if either overload or noise is a problem in which case I turn a knob down to remove the overload or turn a knob up to raise that stage’s SNR.

to be honest, it’s just the technical talk, to backup the impact that software volume control can have on the final output.
But as @Ytheleus mentioned, are you able to hear the difference. That part should give you the answer for this choice.
Even if there is some added noise, but you can’t hear it, does it matter?

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I was thinking about this issue/setup too, it comes down to functionality vs Purity. Not sure if you can really hear a difference but leaving volumio on 100% vol makes sense, like lineouts should be. I just know you shouldn’t have too many volume/gain comtols in the chain, like to keep things simple now.

My old DAC didn’t have a volume control or a remote (but had a gain control Inbetween the DAC and monitors (which also have their own volume controls, which I set and forget).

I used to use the phone buttons for the Chromecast audio volume control, although with the android 11 update that feature is broken anyway (copyright, should be fixed in a future update). Volumio doesn’t seem to have reliable vol control using phone buttons either, maybe when playing through the tidal app.

Can live with using the DAC hardware volume control now, remote is handy.