On 2019-04-27, Christian Weisgerber <naddy@mips.inka.de> wrote:
> It is my theoretical understanding that USB audio gadgets typically
> come with a uhid(4) device, as does yours above, and you would use
> usbhidctl(1) to list and manipulate the available controls.
No, that is wrong.
Looking over uaudio.c, I now see that mixer controls are an inherent
part of the USB audio spec and that the driver automatically provides
them.
So the correct answer is this: If your USB audio gadget attaches
as audioN, use "mixerctl -f /dev/mixerN" to access the corresponding
controls. If you don't specify a device, mixerctl uses /dev/mixer,
which by default is a symlink to /dev/mixer0. You can point this
symlink to a different unit. Alternatively, you can set MIXERDEVICE
in the enironment.
(Personally, I have only used USB audio dongles to add an S/PDIF
output to machines that lacked one, so the mixer didn't really come
up.)
--
Christian "naddy" Weisgerber naddy@mips.inka.de
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