Vorbis for music and longer sounds, to cut down on file size.
However it takes processing to decompress the files on the fly, so PCM and ADPCM are used for the shorter frequently repeated sound effects.
PCM is obviously lossless since it's just a wav, but ends up with the biggest file sizes. ADPCM compresses wavs up to 3.5 times, but does have some impact on tonal quality, so it's used on noisey sounds with a wide spectrum
(footsteps, impacts etc)."