Logical device name for 4-channel microphones?

Logical device name for 4-channel microphones?

[Tanu Kaskinen]

Hi,

What is the best source of information about device names ("front",
"surround40" etc)? Is it the DeviceNames wiki page[1]? That page was
slightly out of date, so I updated and expanded it (review would be
welcome).

I'm looking for information specifically about capture device names. The
wiki page didn't help me there, as it only listed playback device names.
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? If not, what should be
done?

Pulseaudio could just use "hw", but I'd prefer there to be a standard
device name for 4-channel mics. AFAIK, at playback side, some surround
implementations are using multiple devices on one card, and using "hw"
wouldn't work in those cases, while e.g. "surround40" can use the
multiple devices behind the scenes. I would guess that the same could be
the case with some multichannel microphones, and therefore a logical
name like "fourchannelmic" would be better than using "hw".

[1] http://www.alsa-project.org/main/index.php/DeviceNames
[2] https://bugs.freedesktop.org/show_bug.cgi?id=45813

-- 
Tanu

Re: Logical device name for 4-channel microphones?

[Clemens Ladisch]

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.


Regards,
Clemens

Re: Logical device name for 4-channel microphones?

[Takashi Iwai]

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.


Takashi

Re: Logical device name for 4-channel microphones?

[Tanu Kaskinen]

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. 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

Re: 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
> 

Re: Logical device name for 4-channel microphones?

[Tanu Kaskinen]

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.

Alright then, what should be the name? Here's one proposal:
"4channelinput".

-- 
Tanu