Howdy, all
I have one of these: http://www.chordelectronics.co.uk/products_detail.asp?id=63
It's got one of these USB DACs inside ID 08bb:2704 Texas Instruments Japan
The DAC has a single mixer control, Master, which allows you to adjust volume and mute/unmute. The fun thing is that the volume adjustment has no effect whatsoever. On machines running pulse, this means that output will be at 0dB pretty much all the time. (Of course, this is true of non-pulse machines also).
The attached patch disables the Master control, which causes pulse to control levels entirely in software, as it should for this device.
The main downside to this patch is that, while the volume part of the Master control is non-functional, the mute/unmute aspect does work as expected. I couldn't figure out how to change the Master control to just a mute/unmute control, but if someone has suggestions on what to do, that'd be appreciated. Judging by the comments in the code (and contrary to what I wrote in the map comment), I presume the mute/unmute control is the only reason why 08bb:2702 isn't doing this same thing.
Cheers, --xsdg