What's the difference between Master and PCM channels in Alsa?

Question

What is the difference between Master and PCM channels in Alsa, and which one should I manipulate for controlling the output volume?

I have three sound cards (Intel PantherPoint, HRT HeadStreamer and Fiio E10 DACs). The Intel is integrated and comes with both Master and PCM, whereas the other two are external and only have the PCM channel with no Master.

I'm writing a script to toggle between the different soundcards and I'd like to figure out what is the exact setting to fiddle with.

Thanks for your help

Answer 1

With more complex devices, "PCM" affects the audio data played by software, while "Master" also affects everything else going to the speakers.

With devices that do not have an analog mixer, this distinction would not make sense.