I've been having problems with USB sound for some time (it used to work about 6 months ago). I find that any USB sound device that I connect is not recognised, and is not listed by aplay -l I've tried disabling pulseaudio. I've tried purging and re-installing alsa-base, pulseaudio, and pavucontrol. To no avail. I'm using 12.04 LTS. I found the solution: 12.04 does not have the needed kernel module snd-usb-hiface this is introduced in the 3.11.1 kernel and installing that on 12.04 gives USB sound for my equipment. How to install the 3.11.1 kernel is given here:- installing 3.11.1 kernel