Sound pitch
Changes the pitch of all sounds for the specified player. Negative values lower pitch, positive values raise pitch. Pitch will remain altered, even if a new game is started, until sound_pitch is set back to 0. Note that sound_pitch will not affect the pitch of sounds already being played (so a looping sound will not be altered until the next time it starts).
Example:
setplayer[THISACTOR].sound_pitch -1024
...will lower the pitch of sounds as if the player were underwater.