A quick introduction to FM Synthesis

Frequency Modulation (FM) synthesis is a process for creating a wide range of sounds by modulating (changing over time) the frequency of an oscillator using another oscillator.

A "carrier" oscillator is wired so it can be heard, and then a second "modulator" oscillator is wired to the frequency control of the carrier. When the modulator oscillator is at a slow speed and intensity, this creates an effect usually called "vibrato" - but when the modulator is oscillating fast, in the audible range (20hz to 20,000hz), it's called FM synthesis.

As the image above suggests, the resulting frequency modulated wave is much more complex than either the carrier oscillator, the modulator oscillator, or the two simply mixed together and heard.

If your browser supports WebAudio, you can use the tool below to explore a simple FM setup - one carrier and one modulator. If you're not hearing sound, check that your phone isn't on silent.

Using this basic idea we can create extremely complex FM synthesis setups, that generate an almost infinite range of sounds, usually by doing one or all of the following:

1. Adding envelopes to the oscillators, so their level or amount of modulation changes over time.
2. Using more oscillators. These are wired together in complex networks of modulators and carriers, usually called "algorithms". The Yamaha DX7, the instrument that popularized FM synthesis, had six oscillators that could all be used as modulators OR carriers, and they could be arranaged into 32 different algorithm.
3. Using oscillators that can create different wave shapes. On the DX7, all the oscillators only generated sine waves. On later FM synthesizers you often have a wide range of wave shapes available for both modulators and carriers.

Crows Electromusic will be releasing an instrument that uses FM soon - subscribe to our email list if you'd like to be notified when it's available!