Dsp
From Hackepedia
Sometimes you will have two applications trying to access your audio device. Here is an example screenshot from trying to run xmms, when something else is accessing the audio:
the culprit can be disovered with lsof assuming your audio device is /dev/dsp like it is on BSD:
$ lsof | grep dsp firefox-b 14905 frank 1w VCHR 30,3 0t0 38 /dev/dsp0.0 firefox-b 14905 frank 1w VCHR 30,3 0t0 38 /dev/dsp0.0 firefox-b 14905 frank 1w VCHR 30,3 0t0 38 /dev/dsp0.0 firefox-b 14905 frank 1w VCHR 30,3 0t0 38 /dev/dsp0.0
as you can see, one of the websites I am viewing with firefox has claimed access to my dsp first. I must now close that tab in firefox, and restart xmms, and all is well.