DIY Pulse-width modulation (PWM) article explains the basics, then gives you the option of breadboarding your own. Audio applications aren’t discussed, but don’t let that stop you. (Technical) (via Hack-a-Day)

Propellerheads demystification (you may have to get Thor)(*)
• SOS on PWM & string sounds (also explains how PWM itself can be synthesized – if your synth is flexible enough)
• Look at a PWM synth module
• Here’s one on PWM in sound design
• A couple more decent articles: (*)(*)(*)

Bonus tip: A blog about making music with computer software
(a bit more ambitious than In Formant)