[alsa-devel] How to define card specific pcm devices?

Raymond Yau superquad.vortex2 at gmail.com
Wed Aug 29 03:44:18 CEST 2012

2012-8-18 下午12:09 於 "Tanu Kaskinen" <tanuk at iki.fi> 寫道:
> On Sat, 2012-08-18 at 09:26 +0800, Raymond Yau wrote:
> > 2012-8-17 下午10:51 於 "Tanu Kaskinen" <tanu.kaskinen at digia.com> 寫道:
> > >
> > > Ping?
> > >
> > > If card specific pcm definitions are not possible, would it be
> > > acceptable to have a generic "front_left:CARD" or "first_channel:CARD"
> > > pcm, which would transform "front:CARD" or "hw:CARD" into a mono
> >
> > As pulseaudio server use SND_PCM_NO_AUTO_CHANNEL which diable channel
> > conversion, this left channel device only work with other alsa
> > except pulseaudio when your sound card does not support mono.
> So are you suggesting that Alsa doesn't need any changes, because all
> other applications allow automatic channel conversion, and therefore
> this is a PulseAudio specific problem and should be fixed in PulseAudio?

strictly speaking your mic is not a true stereo mic and the channel map is
[left, null] instead of the normal map [left,right] of line-in or stereo mic

the  channel map for those stereo mic which have out of phase left and
right channel is  either [left,-left] or [-right,right]

some stereo mic may has [null,right]

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