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.