Count this article as a bookmark, so I can find the relevant links, the next time I have a sound problem.
I have a recurring problem with sound on Ubuntu 8.10. On my desktop sound almost always stops working after a few hours (or sooner). On my laptop sound is less trouble, but still occasionally does stop working.
Also the volume on the my laptop was far too low. Found by opening the volume control applet and running all the sliders up to the max, I could get the volume to a decent level. One problem solved - after a fashion. Clearly there is an issue if the master volume control is defeated by a non-obvious secondary setting.
Lots of folks are having trouble with sound on Ubuntu, but a fair number are due to configuration issues. Wading through far too many notes, I found something that works:
Re: no sound on Ubuntu 8,10 try to restart alsa
sudo /etc/init.d/alsa-utils stop sudo alsa force-reload sudo /etc/init.d/alsa-utils start
Yep, that worked. Had to manually kill rhythmbox (which was playing music when sound died), and had to re-start the volume control applet. Bit crude.
Seems the base problems are more-or-less well known. Also seems at least one guy came up with instructions for diagnosing audio problems (though more for no-sound-ever problems). The PulseAudio software seems to be at the heart of the problem.