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Dual Operator FM Synths


When "FM" is mentioned in synthesizer circles, the Yamaha DX line often comes to mind, since Yamaha built a very successful family that started the demise (at least for a decade or two) of analog synthesizers. While the DX line uses 4 to 6 operators, dual operator (one modulator, one carrier) FM is more prolific than many realize.

Analog FM

While FM was implemented digitally in the DX line, FM started out as an analog concept (think FM radios). In fact, some analog synthesizers have had FM capabilities from the beginning of the industry. A modular or semi-modular (Arp 2600) can modulate one oscillator with another. Here is a list of non-modular synths, featuring dual operator FM (not a complete list):

Yamaha implementation was based on phase modulation vs. frequency modulation.

Note: Technically, every synthesizer with an LFO routed to pitch is performing two operator FM. However, this article will limit the discussion of FM to cases where both modulator and carrier frequencies are in the audio range (20-20kHz) vs. sub-audio (<20Hz).

Yamaha Revisited

While dual operator FM is often a feature on analog synths, it is the primary synthesis method of some lesser known Yamaha families. The GS and CE lines use two dual operator FM sources. However, this in not true 4 operator FM, since the two sets of operators can not interact.

Casio Implementation

Casio CZ families use "phase distortion", which is similar to Yamaha's FM implementation. The VZ family adds true FM synthesis.