Setup USB sound card on Raspberry Pi

sudo nano /etc/modprobe.d/alsa-base.conf

at the end, add the following line to prevent a lot of debugging information to be written to the syslog file.

options snd-usb-audio nrpacks=1

Volume can be changed by typing: alsamixer

Sometimes it seems people is having problems getting the volume and other settings saved. If having troubles try running alsamixer as root and after exit type:
sudo alsactl store

Then reboot.