According to the docco
“16-bit PCM: This is the default format. The data is uncompressed, so it requires very few CPU cycles to play, but uses 2 bytes per sample per channel (about the same as a typical uncompressed .wav or .aiff file).
8-bit PCM: Also uncompressed, but only uses 1 byte per sample per channel (half the space of 16-bit PCM), and lower audio quality.
ADPCM: A compressed format that requires somewhat more CPU cycles to play, but requires 1/3 of the space of 16-bit PCM. Audio quality is typically somewhat worse than 16-bit PCM but better than 8-bit PCM. Samples are packed in blocks of 36 samples (24 bytes).”
*"The most portable formats for a stream sound are:
.ogg (Ogg Vorbis)
These formats are supported on all platforms, including Windows and OS X, and we recommend that you use them for most purposes.
Files in the .cks format are created using cktool; the audio data can be in the same formats supported by bank sounds (16-bit PCM, 8-bit PCM, or ADPCM).
Streams can also be in other audio file formats; support for these varies by platform. Currently, the following additional formats are supported on both iOS and Android:
.wav (uncompressed, or with �-law or a-law compression)
.mp4 (AAC compression)
.m4a (AAC compression)
The iOS version can read the following additional audio file formats:
.aac, .adts (AAC compression)
.aiff, .aif, .aifc
.m4a (Apple Lossless compression)
.snd, .au (uncompressed, or �-law compression)
The Android version can read the following additional audio file formats: