The sound.btc was created with the 'BTc Sound Encoder 3.0' (https://www.romanblack.com/picsound.htm):
* Open the Sound Library file BTc3_Lib1.SL coming with the BTc Sound Encoder.
* Set the 'Algorithm' to '1 bit'.
* 'Resample .WAV' to 33.000 Hz.
* 'Trim .WAV' to samples 0-362500.
* 'Export binary file .BTC format'.
Oliver Schmidt