Hi Daniel,
Thanks for your helpful replies; responses below.
On Sunday 08 April 2012 15:12, Daniel Mack wrote:
On 06.04.2012 23:09, Alan Horstmann wrote:
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.
What are those issues? Can you elaborate?
These are essentially issues in the way Portaudio interfaces; I am not suggesting driver bugs etc, but in summary:
a) The Audio 4DJ uses fixed _BE format, almost uniquely AFAICT from grepping driver source tree. Portaudio at present requests formats in the host platform endianness - so on a x86 PC an acceptable format is not available from the 'hw' device. Users seem reluctant to use 'plughw'.
b) Subdevices are not enumerated by Portaudio at present, and so only 2 of the 4 channels can be accessed. If the unit had presented a single 4-channel device all the channels would have been available.
The device itself implements 4 audio channels which are synced to each other. In other words: the hardware is not able to only enable one of them and leave the other ones paused or set sample rates individually.
When I implemented the driver, it seem most logical to follow the way the device denotes it channels though. The documentation and silk screen presents them as pairs of stereo, and so the driver does the same thing.
I am just interested whether you think it would be possible for the driver to be modified to support a single 4-ch device, perhaps through a module option?
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 writing?
For this particular device, there wasn't any need yet.
I couldn't see any USB cards there - is that probably correct?
Regards
Alan