My confusion turned out to be with what exactly
alsamixer
does. I was getting playthrough because the "Mic" device
was unmuted in the mixer. So alsa was doing the playthrough
directly.
Well, because alsamixer is a tool which tries to match to all
cards supported by ALSA, it is sometimes a bit confusing.
But we do not have a better solution; ask your manufacturer to
write a GPL'ed UI-Mixer for that certain device.
I somehow had the impression that one used alsa
mixer to set the input levels of various devices that were
available to be opened by software talking to alsa.
What does various devices mean in this case?
But by
experimenting with audacity, I see that with Mic muted in
alsamixer, audacity is able to get input from the Mic
device via alsa. Does this imply that ALL input devices
should be muted in alsamixer and apps are responsible for
reading from the input? For example, it seems to not
matter whether I've muted the CD or not.. AlsaPlayer can
still play a CD.
I guess that alsaplayer reads the CD and puts it out to PCM.
The CD channel is if you have a CD inserted and you've
pressed the play button on the drive. In this case, it
behaves like a CD player. If it is connected via an extra
cable to the mainboard, the drive will output the sound
directly to the soundcard and then adjusting the CD channel
would make sense.
Best regards
ce