Software volume control - does this affect sound quality in a negative way?

[voodooless]

I asked Cambridge Audio about this for their Evo, and they said the volume is internally analogue. They may well have been making it up though! I know other kit does volume in DSPs.

Yes, there are chips that offer analog volume control with digital control. Your AVR is full of them.

 

[charleski]

I'm going to add a link from the Auralic forum which mentions software volume control as a result of a technology implemented in Lumin called Leedh which is advertised to be a 'Lossless Digital Volume Control'

https://community.auralic.com/t/lumin-added-new-volume-control-algorithm/6554

Xuanqian responds as below (copied and pasted from the link) ... implying there is a major problem with digital volume controls ....

The algorithm won’t fix digital volume control major problem.
Let’s say we have a DAC which has dynamic range (DNR) of 120dB. It means you DAC has a 1uV noise floor from the DAC chip itself and the all the analog circuits after that comparing to a maximum of 1V output signal level; this makes 120dB DNR.
When you apply digital volume control, the signal level will drop but the noise floor will probably not drop, or at least will not drop accordingly. If you apply a -40dB volume control, your music signal level will drop to 0.01V, but the noise floor won’t drop to 0.01uV because it is way beyond any of current component’s limitation. Let’s say the noise floor drop to 0.1uV (which I will be very impressed), you will lost 20dB dynamic range. In real world, you will lose way more than 20dB, that’s why digital volume control can make sound so dull when you turn the volume down, you just lost a lot of details in the music.
It is not to say analog type volume control is perfect, all resistors have Johnson noise thermometry it is temperature based noise from physical law. JNT is related to the resistor value because the higher value, the more heat it will create when current flow through. In a very high resolution, low noise audio system, JNT must be considered. However JNT can be very low and beyond audio system’s consideration if the entire system has low impedance design.

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The output of your DAC is going into an amplifier. Let's say your amplifier also has a noise floor of 1uV in its input buffer and has the option of switching in an analog potentiometer to attenuate the signal at the input.

Digital volume control:
signal = 0.01V
noise from DAC =1uV, noise from buffer =1uV. Total noise = sqrt(1uV^2+1uV^2) = 1.414uV
SNR = 20log(1e-2/1.414e-6) = 77dB

Analog volume control:
Signal =0.01V
noise from DAC = 0.01uV. Noise from buffer= 1uV. Total noise = 1uV
SNR= 80dB

Not a whole lot of difference, even assuming the analog pot is perfect.

 

[snapcrackle]

Thanks for the maths

 

[voodooless]

The output of your DAC is going into an amplifier. Let's say your amplifier also has a noise floor of 1uV in its input buffer and has the option of switching in an analog potentiometer to attenuate the signal at the input.

Digital volume control:
signal = 0.01V
noise from DAC =1uV, noise from buffer =1uV. Total noise = sqrt(1uV^2+1uV^2) = 1.414uV
SNR = 20log(1e-2/1.414e-6) = 77dB

Analog volume control:
Signal =0.01V
noise from DAC = 0.01uV. Noise from buffer= 1uV. Total noise = 1uV
SNR= 80dB

Not a whole lot of difference, even assuming the analog pot is perfect.

Picture I once made of another thread:

 

[Tom C]

I have a question that I think is on topic: In a DAC with a built-in physical volume control, and that accepts native DSD, does the DAC perform an internal DSD->PCM->Volume adjustment, then convert to analog audio? Not that I can hear a difference between DSD to PCM conversion and native DSD playback. I can't hear a difference. But I am curious. I would think such an internal conversion is necessary.

 

[voodooless]

I have a question that I think is on topic: In a DAC with a built-in physical volume control, and that accepts native DSD, does the DAC perform an internal DSD->PCM->Volume adjustment, then convert to analog audio? Not that I can hear a difference between DSD to PCM conversion and native DSD playback. I can't hear a difference. But I am curious. I would think such an internal conversion is necessary.

It depends. Some AKM DAC’s have direct DSD playback. The E30 for instance supports this in DAC mode (AK4493). Not all DAC’s chips have such a mode however, and even if they do, it’s not always part of the implementation

 

[RayDunzl]

Compared to using an analog volume control from a pre-amp, or in fact the volume control built into a DAC chip, can software volume control be equally good as the aforementioned?

For example, using the 'software' volume control in an Auralic Mini, or Volumio etc etc?

Lose 1 MSB for every 6.02dB attenuation is the basic rule.

It's really not as bad as you might think.

In the following image, the top trace is full volume, the middle trace shows what it "looks" like with 60dB attenuation using the same visual scale (it looks like there is nothing left), the bottom trace zooms in on the -60dB (1/1000th) version to show what's left, which isvery close to what you started with.

-60dB takes your playback from "loud" to "almost inaudible".

The traces represent "voltage" that would be output by the DAC.

 

[BJL]

Lose 1 MSB for every 6.02dB attenuation is the basic rule.

It's really not as bad as you might think.

In the following image, the top trace is full volume, the middle trace shows what it "looks" like with 60dB attenuation using the same visual scale (it looks like there is nothing left), the bottom trace zooms in on the -60dB (1/1000th) version to show what's left, which isvery close to what you started with.

-60dB takes your playback from "loud" to "almost inaudible".

The traces represent "voltage" that would be output by the DAC.

I have found that 32 bit digital attenuators sound generally fine at most listening levels but soft listening levels they suffer. I have found that 24 bit digital attenuators sound poor at most levels.

This isn't by measurement, just my listening experience. The 24 bit control that I auditioned was irritating for music. The 32 bit was fine until I turned the volume down low. This was comparing with Placette precision analog controls. These days I use a Pioneer AVR, which I suspect uses an analog ladder attenuator on an IC, and sounds fine whatever it is. Probably if I wasn't comparing with the Placette attenuators, I wouldn't have noticed the differences, at least with the 32 bit control.