[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
Fri Jun 13 23:40:47 CEST 2008

Jon Smirl wrote:
> On 6/3/08, Erik Slagter <erik at slagter.name> wrote:
>> 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.
> Write this up for the Free Linux Driver project.
> http://lwn.net/Articles/276973/
> http://www.linuxdriverproject.org/twiki/bin/view/Main/DriversNeeded
>>  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 ;-)
>> _______________________________________________
>>  Alsa-devel mailing list
>>  Alsa-devel at alsa-project.org
>> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel

BTW, issues 3,4 are my fault: alsamixer calls the mixers all "speaker-1" 
but if you use amixer, you'll see that this is actually one device with 
separate mixers for front, side, back, etc. So it's logical it only has 
one mute knob.

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