[alsa-devel] Logical device name for 4-channel microphones?

[Takashi Iwai]

At Tue, 24 Apr 2012 18:28:14 +0300,
Tanu Kaskinen wrote:
> 
> On Tue, 2012-04-24 at 16:09 +0200, Takashi Iwai wrote:
> > At Tue, 24 Apr 2012 16:08:45 +0200,
> > Clemens Ladisch wrote:
> > > 
> > > Tanu Kaskinen wrote:
> > > > My problem is that I'd like to make Pulseaudio handle 4-channel webcam
> > > > microphones[2], but I'm not aware of any input device names for
> > > > 4-channel devices. Are there such device names?
> > > 
> > > These device name are useful only for device types that are generic
> > > enough.  Four-channel microphones aren't.
> > 
> > Hm, we have already surround51 or such specific one, so it's not too
> > bad to have a definition for multi-channel mics.  OTOH, surround51 &
> > co were the possible cause of confusions, as there are way too many
> > surround types.  A generic type with the channels argument might be
> > more generic?
> > 
> > In anyway, I think it's fine to define some new generic name.
> 
> From Pulseaudio point of view using "hw" should be fine if you can
> guarantee that any current or future 4-channel mics can be opened in the
> 4-channel mode using the "hw:CARD" device name.

Such a thing can be never guaranteed with "hw" :)
The hw provides nothing but what kernel driver provides.  And the
hardware might be a link of two stereo streams.


Takashi

> I'm just worried that
> there might be cards that split the four channels to e.g. two stereo
> devices, "hw:CARD,0" and "hw:CARD,1", and then "hw:CARD" won't work. I
> might be mistaken, but aren't there some such cases with playback, which
> have to be opened with the "surround" device names to get all the
> channels?
> 
> The "surround" devices also guarantee some specific channel mapping,
> which may not match what "hw" uses, which is another reason to prefer
> "surround" over "hw", but I don't think this applies to input side.
> Therefore, the only possible problem that I can see with "hw" is that it
> might not provide all channels.
> 
> -- 
> Tanu
>