FM — Frequency Modulation
When one oscillator modulates another's pitch fast, magic happens.
Speed up an LFO until you can hear it. Brand new sounds appear.
// WHAT IT DOES
If you slowly speed up an LFO modulating pitch (vibrato), it eventually goes so fast it stops sounding like a wobble and starts creating brand new frequencies. Welcome to .
Two oscillators: the 'modulator' (the fast LFO) and the 'carrier' (the one you actually hear). The modulator wiggles the carrier's pitch thousands of times per second. The result has 'sidebands' — extra tones above and below the carrier that you couldn't get from a single wave.
This is how the Yamaha DX7 made all the famous '80s bell, electric piano, marimba, and metallic bass sounds.
- • FM gets you sounds that subtractive synthesis literally can't produce — metallic, glassy, bell-like timbres.
- • It's CPU-cheap because each 'instrument' is just a few sine waves modulating each other.
- • Even one pair (1 modulator + 1 carrier) gives you a vast palette.
// SEE & HEAR IT
▸ An LFO is a slow oscillator that controls something else. Pick the target to hear vibrato, filter wobble, or tremolo.
▸ HOW IT WORKS
- • Sidebands appearing above and below the carrier as rises.
- • Inharmonic 'metal' when ratios are non-integer.
- • Most of the 'character' arriving in the first 200 ms (modulator ).
▸ WALKTHROUGH (4 steps)
- 1. DO: Use an FM-capable synth (Operator, FM8, Dexed). Init to 2 sines: mod + carrier.▸ LISTEN: Just a sine — modulator off.
- 2. DO: Bring modulator level up slowly.▸ LISTEN: Sidebands appear; brightens and develops.
- 3. DO: Set modulator ratio to 3.5 (non-integer).▸ LISTEN: Bell / metallic clang.
- 4. DO: Give the modulator a fast envelope (A=0, D=200 ms).▸ LISTEN: Classic FM electric piano: bright tine , mellow body.
▸ COMMON MISTAKES
- ✗ Cranking modulation index to max and getting noise instead of tone.
- ✗ Ignoring modulator envelope — FM 'sounds plastic' without it.