Comment 8 for bug 331130

I agree with Damien--my experiments on my EeePC 901, using Audacity similarly, bring me to a similar conclusion. The "left" mic channel appears to be the difference, and the "right" mic channel is the sum.

This causes a problem for me when I download and try using Skype (version 2.0.0.72) [I know, I'd prefer something open sourced, like Ekiga, but 1) I got rid of Gnome for a space savings of over 800MB, and 2) I need something cross-platform to communicate with family members.] Skype's audio input selection is ALSA-aware, but doesn't let you specify channel information, and it appears to select the Left mic. channel on my EeePC, which is just that "difference"--not usable. So, as an experiment, I crafted a ~/.asoundrc clause to swap the mic. channels for a new ALSA device or whatever the proper term is, calling it "skype" like this:

pcm.skype {
  type route
  slave.pcm "hw:0,0" # Or, if you've followed examples which sets up a "dsnooped" label, then you could say "dsnooped" here instead (if you wanted to use software-mixed-input.)
  ttable.0.1 1
  ttable.1.0 1
}

Then, in Skype, I select the "skype" ALSA label, and now I can hear myself when performing a test call, nice and clearly.

Yeah, it'd be great if there was a way, using the .asoundrc file, to subtract the "difference" channel from the "sum" channel, but I imagine you'd have to investigate using the LADSPA plugins for that, or use JACK, or PulseAudio, or something complex like that. (Or, it'd be nice to have an ALSA module parameter to tell it to do that mixing in kernel space for us, giving us a nice clean mono mic. channel...)

But, anyway, again, this is my recent experience on an Asus EeePC 901, using Debian (Lenny) [I know, not Ubuntu, but I had found this thread to be very informative, and wanted to add my experience]; I'd recompiled ALSA (version 1.0.19, under kernel 2.6.26-1-686), and had to add the line 'options snd-hda-intel model=eeepc-p901' to /etc/modprobe.d/alsa-base, not that that really changed anything (but before adding that options line, I had had a line in my /var/log/boot where the snd-hda-intel module couldn't determine the model information, which disappeared when adding that options line.) I'd used http://www.kernel.org/doc/Documentation/sound/alsa/HD-Audio.txt (and HD-Audio-Models.txt.)