"Note that you most likely will have to change the sample rate, even if you
already have OGG files that are supposed to replace the music that ships with
the game. The sample rate needs to be at 22050 Hz, not 44100 Hz. This makes the
music sound worse indeed, but if you don't do that, you will have the file
playing at half time. Which is no good. In Audacity, you can find the thing for
changing the sample rate in the lower left corner of the window. Change that to
22050, then export to OGG and you should be fine."

source: http://forums.wolfire.com/viewtopic.php?f=7&t=17652