[alsa-devel] USB audio devices on Audio 4DJ and similar
gineera at aspect135.co.uk
Fri Apr 6 23:09:21 CEST 2012
Hi Daniel and Alsa folks,
At present I am involved with resolving some issues that have arisen from
people using the Audio 4DJ interface with Portaudio, and I hoped it would be
OK to check a few Alsa details with you? Unfortunately I have limited
experience of USB audio.
Apparently the 4 audio inputs/outputs appear as 2 stereo sub-devices on the
first device, rather than a single 4-channel device - is this correct?
Assuming that is correct, does that arise as a result of the intrinsic nature
of the interface, or is it by developer choice in the driver (for example so
that it can be opened as 2 stereo streams)? Is there (or could there be) a
way to change this, eg by module option or udev rule? I notice in the source
#define CHANNELS_PER_STREAM 2
Is there a way at present that the device can be accessed as a single
4-channel stream other than by creating a custom ~asoundrc with a pcm
definition using 'multi' to join the 2 stereo streams?
I don't see any USB audio units having files in /usr/share/alsa/cards; is it
not relevant, not normally necessary or something no-one has got round to
I appreciate any clarification you can bring.
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