The synthesizer-related classes Synth, SynthSound, SynthParameters have already been covered on the overview page. This leaves only SynthOscillator, SynthEnvelopeGenerator, and SynthVoice. SynthVoice is by far the most important, so let's start with that. I'm not going to pore over every line of code; instead my goal is to point out what's important to help you understand the code as you read it for yourself.