[pulseaudio-discuss] Splitting a sound card

Tanu Kaskinen tanuk at iki.fi
Wed Aug 29 05:08:43 PDT 2007

On Wed, Aug 29, 2007 at 12:52:21PM +0200, Jan Kasprzak wrote:
> I have read the FAQ, where it is described how to join several sound cards
> into one output. What I would like to do is the opposite:
> 	I have a 4-channel sound card, and I would like to use it as two
> independent sinks, with two channels each (for example, one for the speakers,
> and the second one for the headphones).

I believe this is currently impossible. You can load
module-alsa-sink with only two channels, and with
channel_map you could probably even control which channels
go to which physical output. Then you would only need to
load another instance of module-alsa-sink, but with
different channels. But, the second loading will fail,
because the device is already opened. If the card supports
hardware mixing (improbable), this trick might even work.

If it doesn't do hw mixing, there would need to be some
explicit support in Pulse for splitting a soundcard. And
that support doesn't exist, AFAIK.

I don't think this is an unreasonable feature to wish,
though. Maybe it will be implemented some day. (I'm not

> I want (for example) ekiga to send an
> "incoming call ringtone" to both outlets, while the rest of the call
> should go to the headphone outlet only.

Does Ekiga really support such feature? I had a quick look
at its manual, and it seemed only care about a single output
device, so how did you intend to separate the ringtone from
other output? Manually switch to a different sink?


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