Sona 0.50 Source

Sona 0.50/doc/format-pcm.txt

SonaWave is the PCM instrument format in Sona. The recommended file
extension is ".swav".

The PCM format is 8-bit unsigned mono at ~10650Hz. Only bytes $00~$FE are
valid, samples with value $FF need to be replaced with $FE. The waveform
must be padded to 32 bytes, add $7F bytes until the next boundary if needed
($7F is the center value).

After the PCM data, add 32 more bytes, all with value $FF. This marks the end
of the instrument.