PulseAudio

PulseAudio is an audio framework for Linux that was allegedly introduced in Ubuntu and some other Linux distributions before it was ready.

Allegro
PulseAudio broke sound in Linux games using the Allegro library, a cross-platform game programming library similar to SDL, because the PulseAudio developers did not add support for the Sound Blaster-style unsigned 16-bit sample format used by Allegro. There appears to be a workaround.