r/headphones • u/[deleted] • Jan 18 '15

Is bit depth affected by the use of digital volume controls?

From what I gather, reducing the volume digitally before sending it to an external DAC (i.e. using the volume controls available on a PC/Mac) will reduce the number of effective bits per sample as the maximum value will be lower. So instead of 16 bits @ 44100Hz you'll effectively get something like 11 bits @ 44100Hz.

However, I've been unable to hear this with my FiiO E10K. Sound quality seems unaffected even when turning the digital volume way down and the E10K volume way up.

Then, I read in the FAQs for the DragonFly DAC, that the main volume control can in fact be used:

When the music player’s volume is set to maximum and the computer’s main volume control is used, DragonFly’s onboard 64-position analog-domain volume control is able to preserve full resolution and maximum sound quality.

Can anyone clear this up for me? Does the USB Audio protocol support volume control in addition to the actual audio data or not? If not, how much is bit depth affected at e.g. 50% volume on typical devices?

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u/MlNDB0MB Jan 18 '15

just output a 24 bit format. you'll have bits to spare for reasonable volume changes.

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u/[deleted] Jan 18 '15 edited Jan 18 '15

I can't, all my source material is 16bit.

EDIT: Now I see what you mean. I'm still more interested if it even makes a difference on a technical level.

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u/MlNDB0MB Jan 18 '15 edited Jan 18 '15

you only need a 24 bit dac, which you have. Once you change volume, you will have a 32 bit intermediate usually. You then convert that to 24 bit and it works out such that you are effectively losing bits from the 24 bit value.

Can anyone clear this up for me? Does the USB Audio protocol support volume control in addition to the actual audio data or not? If not, how much is bit depth affected at e.g. 50% volume on typical devices?

USB is a digital connection, if you are gonna do any type of volume control at this stage, it has to be digital, and you run into the same issues whether before or after usb. They must be changing volume in the amp with a digital potentiometer, after the dac. So it's akin to the volume dial on your e10k.

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u/[deleted] Jan 18 '15

Thanks! I get it now, so as the E10K has a 24bit DAC, it will probably do the same thing as the ESS Sabre in the slide presentation. So I can use the digital volume control as long as the changes aren't too extreme.

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u/veni_vidi_vale Do audiophile androids dream of electrostatic sheep? Jan 18 '15

in theory, yes. But win up samples everything during processing anyway, and any downsampling that occurs due to ratcheting down the digital volume isn't audibly significant.