On Mon, 11 Jul 2016, John Westwood wrote:

I think the MTP stuff is a red herring. I checked syslog when I use a DAC that works (Audiolab MDAC) and that has the MTP lines too, but it doesn't have the warning line about Unlikely big volume range.

In addition, the working DAC has the following lines which are not present the non-working DAC:

Jul 11 19:56:35 atlas kernel: [83940.049124] input: Lakewest Audio Audiolab M-DAC as /devices/pci0000:00/0000:00:1d.1/usb7/7-2/7-2:1.0/0003:0451: ADAC.0002/input/input12 Jul 11 19:56:35 atlas kernel: [83940.104367] hid-generic 0003:0451:ADAC.0002: input,hiddev0,hidraw1: USB HID v1.11 Device [Lakewest Audio Audiolab M-DAC] on usb-0000:00:1d.1-2/input0

With the non-working DAC I get these lines instead:

Jul 11 19:56:25 atlas kernel: [83930.079063] usb 7-2: Warning! Unlikely big volume range (=65535), cval->res is probably wrong. Jul 11 19:56:25 atlas kernel: [83930.079067] usb 7-2: [2] FU [PCM Playback Volume] ch = 1, val = -32768/32767/1

I think maybe the problem is similar to this one:

https://groups.google.com/forum/#!topic/linux.debian.kernel/HwwkRkbL5aY

Is my problem a bug in snd-usb-audio? Or am I doing something wrong? I would really appreciate some thoughts on this, I feel like I'm talking to myself :-(

Considering that you're not really doing anything, you're probably not doing something wrong. :-)

On the other hand, you're likely to get more of a response if you direct your questions to the person who solved the problem mentioned in that Debian bug report, and if you CC: the sound developers' mailing list rather than the general USB list.

Alan Stern