What is the snd sound file format?

The type of encoding depends on the value of the 'encoding' field (word 3 of the header). Formats 2–7 are uncompressed PCM, therefore lossless. Formats 23–36 are ADPCM, which is a lossy, roughly 4:1 compression. Formats 1 and 27 are μ-law and A-law, respectively, both lossy. Several of the others are DSP commands or data, designed to be processed by the NeXT MusicKit software.