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A complex oscillator pairs two oscillators so one FM- or AM-modulates the other to enrich a simple wave

Concept L2First instrument E · Modular, Eurorack, grooveboxes & dawless B · Sound design & synthesis

A complex oscillator couples two oscillators: one (the modulator) changes the frequency (FM) or amplitude (AM) of the other (the carrier). At low modulation depth the result is gentle vibrato or tremolo; at audio-rate depth, sidebands appear, adding harmonic and inharmonic partials to a simple carrier. Because even two sine sources suffice, complex spectra emerge from minimally complex material — this is the defining West Coast route to harmonic generation without subtractive filtering.

Examples

Carrier 440 Hz sine, modulator 110 Hz sine at audio rate: FM produces sidebands around 440 Hz (e.g. 330 and 550 Hz). Raising the depth adds further sidebands, moving the tone toward bell-like or metallic timbres.

Assessment

Describe how a complex oscillator’s output spectrum changes as modulation depth rises from zero to high. Which new frequencies appear, and are they harmonic or inharmonic relative to the carrier?

Prerequisites — understand these first

Don't confuse with

Buchla complex oscillators pair a modulation oscillator with a principal oscillator to produce timbres unavailable from single-oscillator designs

Sources

“using a pair of [oscillators](https://learningmodular.com/glossary/oscillator/ "Glossary: Oscillator") (sometimes combined into what's called a "[complex oscillator](https://learningmodular.com/glossary/complex-oscillator/ "Glossary: Complex Oscillator")") where one modulates the frequency ([FM](https://learningmodular.com/glossary/frequency-modulation/ "Glossary: Frequency Modulation")) or amplitude ([AM](https://learningmodular.com/glossary/amplitude-modulation/ "Glossary: AM")) of the other”

corpus · west-coast-synthesis-learning-modular-glossary · chunk 1

Taught in modules

Unlocks (2) — atoms that build on this