Comment 5 for bug 368121

More investigation:

Ripped out ALSA, installed OSS4. CPU usage went down slightly, sound quality improved.

Installed glib 2.18 from source, then installed mpd 0.15 from source, turning off everything except MP3, MP4 and OSS. CPU usage went down a bit more, glitching stopped even with the buffer size turned back down to the default.

So I have something that works again (installed via checkinstall so I can go back to provided packages when the problem is fixed).

Looks as if it's an MPD problem, not an ALSA problem; and it's somewhat improved in 0.15, but you'll have trouble building that for Ubuntu because it needs a much newer glib than Ubuntu has in the repos.

(To save you some time, the configure script for mpd says it needs glib 2.6, but glib 2.6 is incompatible with GCC 4.3, so you'll want something even more up to date. I had success with glib 2.18, which is the current non-development release.)

((Quite why Ubuntu still ships a version of glib that's about 5 years old, I don't know.))