Frequency modulation (FM) is a synthesis technique that involves using one oscillator to modulate the frequency of another oscillator. FM synthesis is often associated with the Yamaha DX7, a classic digital synthesizer from the 1980s that used this technique extensively.
In FM synthesis, the modulating oscillator (referred to as the modulator) is connected to the carrier oscillator (the oscillator whose frequency is being modulated) through a modulator-to-carrier frequency ratio. The modulating oscillator’s frequency is then used to modulate the frequency of the carrier oscillator. The result is a complex waveform that contains a rich spectrum of harmonic and inharmonic overtones.
The amount of modulation is controlled by the modulator-to-carrier frequency ratio and the strength of the modulation, which is often controlled by an envelope or LFO. As the modulation depth increases, the harmonic and inharmonic overtones become more pronounced, resulting in more complex and evolving timbres.
FM synthesis can be used to create a wide range of sounds, from bell-like tones to metallic and industrial sounds. It is often used in electronic music genres such as techno, ambient, and experimental music.
In modular synthesis, FM can be achieved using a dedicated FM oscillator module or by patching the output of one oscillator into the frequency modulation input of another oscillator. FM can be a powerful tool for creating unique and evolving sounds in a modular synthesizer setup.