Synthesizer Boot Camp is an excellent series of synth tutorial videos create by Simon Cann. I'll be highlighting some of these videos in the coming posts.
Finally we focus on FM synthesis, which features the pitch of one oscillator (the carrier) being modulated by the output of another oscillator (the modulator). The carrier output contains a series of sideband frequencies. Adjusting the volume of the modulator (the "modulation index") alters the number and strength of those sidebands, and the adjusting the modulator and carriers to different frequencies alters the frequencies of the sidebands.
9 mins in length: