On Sun, Oct 03, 2010 at 11:22:00PM +0200, Matti Picus wrote:
My X-FI Surround USB card is barely usable. pulseaudio will let me control the volume levels, alsa support cannot view any volume controls.
But audio streaming does work for you? I heard people reporting success with this kind of hardware.
How can I contribute to better support for this card under alsa? I would like to get to the point where amixer can control the analog input/output volume levels.
As for the volume controls, there are merely two ways how they can be implemented on USB soundcards. One is as feature unit control, and the other is a proprietary vendor specific USB request. You should start having a look at the USB descriptors the devices exports (by running "lsusb -v").
In case the card does not offer a standard way to control the volume levels, you need to trace how the Windows driver does it by sniffing the communication while performing this specific operation, either with an USB hardware analyzer, or with a piece of software. There are some projects aiming for this, but I can't give you any recommendation. Just try some of these, maybe:
http://www.google.com/search?q=windows+usb+traffic+sniffer
Once you found out how they do it in Windows, you can add device specific mixer handlers, as they exist for other hardware. Have a look at sound/usb/mixer_quirks.c.
Hope that helps,
Daniel