2010/12/7 Eliot Blennerhassett <linux@xxxxxxxxxxxxxxxx> > Thanks Raymond, > > On 03/12/10 15:33, Raymond Yau wrote: > >>> Greetings, > > > > > >>> There is only a single mic on this netbook. However, the alsa device > >>> shows up as stereo, and the right channel carries an inverted copy of > >>> the left channel. > > > > > http://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=59c774ed5ee00e9623a204c3234191d6a6d8cf7a > > Commitlog was "Add route_policy copy to HDA-Intel.conf for capture > Since some digital mics have the phase-inversion problem in one channel, > adding both channels for mono stream results in the noise. Use > route_policy copy to avoid that situation." > > As far as I can guess, the commit helps when an application asks to > record mono from the stereo device, by copying L rather than summing L+R > > My machine already has this, however it doesn't really fix the root of > the problem. > https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/639846 The route plugin is only used when the application are alsa 's default pcm/ctl device for hda-intel if you fall back to use dmix/dsnoop pulseaudio is using front device for capturing (i.e. changing PCM Playback volume affect pulseaudio recording ) > > Because the internal mic appears as a stereo device, rather than a mono, > applications can open it as stereo. > > Only later when the resulting signal L+R is sent to a mono output does > the signal "disappear". > > So I'm back to wondering how to force an app (primarily PulseAudio) to > see the mic as mono? > > you have to ask PA developer _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
