[alsa-devel] Specs available for Sweex External 5.1 with digital in/out USB 2.0 / C-Media CM6207

Erik Slagter erik at slagter.name
Tue Jun 3 22:05:52 CEST 2008

Hi there,

Today I bought this sound device, I was hoping it had the C-Media CM650? 
USB chip which is already supported by alsa (according to the list).

Instead it has a CM6207 inside.

The good news is that it supports USB audio "class" and it's more or 
less usable, some mixer outputs are available (although they're all 
called "speaker") and with some trickery the various outputs can be used.

The other good news is that Sweex supplies the "official" datasheet from 
C-media which I think is quite interesting and may very well be useful 
to resolve the last few issues.

These are the actual issues (so far, I didn't yet test it exhaustively):

  - using 2 channel output the sound is garbled; it looks like the 
"wrong" 2 channel alt setting is used (output of 
/proc/asound/card?/stream0 on request), 4/6 channel output is OK though.
  - some high squeeking noise although C-Media claims the IC to be 
high-end (or maybe their definition of high-end differs from mine ;-))
  - all outputs are labelled "speaker 1"
  - only two outputs have a mute knob, the others cannot be silenced in 
any way, only turned down
  - one of the two outputs with the mute knob doesn't appear to do 
anything (or maybe it's the sp/dif output?)
  - the other (with mute) controls the front output
  - the others (without mute) don't seem to do anything at all

Is this a typical case of (a) bug(s) in the usb audio class driver or 
should I think of "vendor extensions" here?

Would any of the developers have some interest in the datasheet of the 
chip and or any data of this thing? Of course I'd like it very much if 
the device would be fully supported but I can only ask nicely ;-)
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