This is where you find programming examples as well as hardware information about the SID, the soundchip inside the C64. This section also contain information related to music programming on the c64, such as music file formats and other things like that.
This section exemplifies how to play a tune in your own demos/games. The tune itself is done elsewhere, in a editor like JCH/DMC/SDI etc, or coded directly in assembler.
Detailed examinations of the waveforms.
This section deals with code to generate music. (Not just playback of readymade music.)
Is it a 6581 (the old one) or a 8580 (the new one) SID in your machine?