На вскидку:
Sonic Academy: Synthesis 101 - Subtractive Synthesis
Sonic Academy: Synthesis 101 - FM Synthesis
Native Instruments Absynth 3. Tutorial DVD
MacProVideo - A/V Fundamentals 201 - Analog Synthesis in a Digital World
MacProvideo - Richard Lainhart: Advanced Synthesis
Ableton Synthesis With Operator
Но они правда не онлайн.
Ну и куча туториалов на Youtube.