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

[Daniel Mack]

Hi Alan,

On 11.04.2012 12:59, Alan Horstmann wrote:
> 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'.

Erm. Class compliant USB cards speak _LE formats only, and I'm not aware
of any hardware that is able to switch endianess on a run-time
configuration base. Does that mean PortAudio is unable to feed these
cards on BE hosts like PowerPC? Does the sound output endianess always
have to match the audio stream format? I certainly doubt that.