Frequency modulation or FM uses two oscillators in order to create a signal. Instead of these oscillators adding together, they interact in an unprecedented way. Similar to how an LFO can modulate the frequency of a signal, a VCO can do the same. In this demonstration the top signal acts as a modulator and the bottom signal is the carrier. When the FM Depth is adjusted the resulting waveform appears. The volume slider can be used to hear the waveform. Note: The waveform is not heard as it is rendered. Because audio rate signals move too fast and LFOs move too slow, compromises had to be made in order to both visualize and hear the audio. That being said, the animation is merely a simulation.

The first FM synthesizer was released by Yamaha in 1980. Yamaha had previously acquired exclusive rights to Stanford Patented FM technology after prototyping an FM synth in 1975. This synthesizer was known as the GS-1. However, the most well known FM Synth is the DX7. FM synthesis quickly became popular after the DX7s release in 1982 due to it being one of the first commercially available digital synthesizers. What separated FM synthesis from the standard subtractive synthesis was its ability to create complex waveforms and natural sounds. Often times FM synthesis is used to create percussive sounds like bells, chimes, and other metallic noises.