[alsa-devel] USB audio devices on Audio 4DJ and similar

Alan Horstmann 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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