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.)
--
Eee PC internal microphone inverts noise cancellation
https://bugs.launchpad.net/bugs/331130
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