What's the best way to adjust volume? (Using PCM1794A)

Hi Astro,

You are correct that the digital attenuation will decrease your resolution after you have exhausted the headroom between the ENOB of the DAC and the ENOB of the digital audio. While digital attenuation will reduce the total resolution available, the DAC in most cases, if not all for a use case, will be able to perform at a higher ENOB than the source audio. Let's say the source audio is at 17 ENOB, and the DAC can perform up to an ENOB of 22 bits, then you have the headroom of 5 bits of resolution for attenuation before the signal quality of the audio is actually effected by digital attenuation. And once it does get that low, it becomes harder, if not impossible, for the human ear to detect any distortion. With the PCM1794A, the digital attenuation would have to be performed in the audio source, while using the PCM1792A can perform digital attenuation since it has software control.

The above will be true for any kind of digital attenuation, but as stated above, the headroom of the DAC will affect how much headroom is available before the signal quality is truly changed. Therefore, the only other way would be an analog control. And you have proposed changing the 10k Iref resistor. I do not recommend using this method as our testing and verification has been done with a precision 10k ohm resistor, and we do not have test data outside of this. You are welcome to test this method yourself and I would be interested in the results.

Another analog approach to volume control would be to place resistor dividers with pots on the input to the TPA6120A2. This would allow you to control gain with the turn of a pot, and have no effect on resolution. This solution however does not allow for digital control of volume.

For each situation these options have positive and negatives that will fit certain applications.

Justin

Hi Astro,

The best option would probably be the second option so that you don't have the inputs to op amps interfering with each other.

Justin