(Re-sending including alsa-devel and more information.)
Hello there.
I'm a developer for Mixxx, the cross-platform open-source DJ software which uses PortAudio and we've been trying for a long time to track down the cause of "horrible mic sound" as documented in our bug: https://bugs.launchpad.net/mixxx/+bug/900364 The resulting recorded audio sounds about 50-60% lower pitch with crackles and it only happens with the ALSA API on Linux and only with certain (mostly Intel-based) audio devices.
I have just discovered by testing in Audacity (which also uses PA) that the problem occurs when PA (and therefore ALSA) is asked to open just one channel of a sound input device yet the device (or ALSA) seems to stream two anyway. I have been able to reproduce the problem in Audacity (which also uses PA) when selecting the ALSA API and mono recording, but it works correctly when I change it to stereo recording.
I'm suspecting there's a miscommunication between PA and ALSA or ALSA and the sound hardware where either the lower level is saying its input(s) can only be opened in stereo and the higher level (or the application above it) ignores that, or the lower level says it's fine opening mono but then misbehaves.
How can I find out which, whether it's ALSA, PA, or the sound hardware at fault?
Sincerely, Sean M. Pappalardo "D.J. Pegasus" Mixxx Developer - Controller Specialist