@audio/synth-fm

FM (phase modulation) — Chowning 1973, single-op or serial ops stack, per-op feedback + index decay; bell/epiano presets; FFT sidebands match Bessel J_k to 0.00%

npm install @audio/synth-fm

import fm, { bell, epiano } from '@audio/synth-fm'

Chowning 1973 FM synthesis ("The Synthesis of Complex Audio Spectra by Means of Frequency Modulation," JAES 21(7)), implemented as DX7-style phase modulation. Single operator by default, or a serial ops stack (innermost-first, each op's output phase-modulates the next, last modulates the carrier) — per-op ratio/index/feedback/indexDecay. bell and epiano are FM-classic presets built on the same kernel.

fm(440, { ratio: 1.4, index: 10, indexDecay: 2 })   // → Float32Array
bell(440)                                            // Chowning's inharmonic bell/gong
epiano(440)                                          // 2-op DX7-style e-piano

| Param | Default | | |---|---|---| | freq | — | Carrier Hz (positional) | | ratio | 2 | Modulator:carrier ratio (single-op form) | | index | 5 | Peak modulation index, radians | | indexDecay | 0 | Index decay time constant, seconds (0 = static) | | indexFloor | 0 | Index floor after decay | | feedback | 0 | Modulator self-feedback, radians | | ops | — | Serial modulator stack [{ratio, index, ...}] — overrides the single-op params | | duration | 1 | Seconds | | attack / release | 0.005 / 0.1 | Seconds | | amp | 0.8 | Peak amplitude | | fs | 44100 | Sample rate |

Use when: classic FM timbres (bells, e-piano, brass-ish tones); ops for multi-operator stacks.

Part of @audio/synth — the synth family umbrella.

MIT © audiojs