I thought that using a USB sound card with Linux would be easy, just plug and play, but I was wrong, it seems. Plugging in the Terratec Aureon Dual USB (ID: 0ccd:0077) that I bought rendered a promising output from dmesg and lsusb, and lsmod showed that even relevant modules were loaded. The problem was that mpd and other programs did not find any way to actually output sound to any device. They had the firm belief that my system was lacking any sound card. Maybe I would need some sound related packages?
aptitude install alsa-base alsaplayer alsaplayer-text alsa-utils
No luck… The mpd configuration file /etc/mpd.conf seemed mostly confusing when it came to output devices, and the wiki page it referred to did not help either. A search with Google on the USB ID was helpful though, as usual. Someone with the alias BigRon also had problems with Debian and this Terratec USB sound card. The results from his attempts, documented with verbose output, was similar to mine. User bandan’s reply was the beginning of the end of my trouble! I had to edit /etc/modprobe.d/alsa-base.conf to comment out a line preventing USB devices from becoming the first (default) device, substituting it for a line with the opposite effect.
## Keep snd-usb-audio from beeing loaded as first soundcard<br/>
#options snd-usb-audio index=-2
# Fix from http://forum.doozan.com/read.php?2,4119,4166<br/>
Now I was at least able to get alsamixer to acknowledge the mere existence of a sound related device, but alas it chose an input only device (most likely my Logitech webcam with microphone) as the default device even though it called the Terratec one default by name. Luckily for me the just mentioned forum thread linked to a more substantial thread describing the problem in more depth. I added myself and the mpd user to the audio group, to make sure that there would not be any problems with permissions regarding the devices
addgroup jadler audio addgroup mpd audio
I was still unable to play anything (without explicitly chosing what Alsa refers to as sound card 1). So I kept trying the stuff that had worked for the person reporting in the forum, creating an /etc/asound.conf file with basically the same content as suggested in the last thread referred to above, but changing all references to hw:0 to hw:1, and from card 0 to card 1. Now mplayer works, but I still can’t get mpd to do its thing.