FM between two detuned oscillators produces inharmonic noise suitable for hi-hats and cymbals

When two oscillators are patched so one frequency-modulates the other (or phase-modulates in PM mode), and the carrier-to-modulator ratio is non-integer, the sidebands produced are inharmonic — they don’t relate to a musical fundamental. Intentionally mistuning the oscillators amplifies this inharmonicity, creating a dense, clangorous noise that mimics the metallic quality of cymbals and hi-hats. This is more timbral varied than filtered white noise, which lacks the frequency structure of metallic objects, and far more module-efficient than the Roland TR-808’s approach of mixing six detuned square waves. Harmonically complex waveforms (saws, squares) are preferred for the modulator because they generate richer sidebands; sines produce fewer.

Examples

Patch: OSC1 (saw/square out) → FM input of OSC2. Take output from OSC2. Result is inharmonic clangour before any filtering. Then add HPF to remove fundamental — this transforms the tonal FM sound into metallic texture.

Assessment

Patch two oscillators in FM configuration, set them to a non-integer ratio, and listen. Then retune to a perfect integer ratio (1:1, 1:2) and describe the timbral difference. Explain why the non-integer ratio is desirable for percussion.