@synthlet/lfo

A low-frequency oscillator with eleven shapes, as an audio worklet

Part of Synthlet.

The modulation source. Web Audio's OscillatorNode gives you four waveforms and none of the ones modulation actually wants — no sample-and-hold, no exponential ramps, no single-sample impulse — and no gain or offset without two more nodes. This is one node with all of it.

It emits a signal, one value per sample, so a slow sine on a pitch or a gain is smooth rather than a 344 Hz staircase.

Install

npm i @synthlet/lfo

Or npm i synthlet for every module at once.

Usage

import { registerLfoWorklet, Lfo, LfoType } from "@synthlet/lfo";

const ac = new AudioContext();
await registerLfoWorklet(ac);

const osc = new OscillatorNode(ac, { frequency: 440 });
osc.start();

// ±10 Hz of vibrato at 5 Hz
const vibrato = Lfo(ac, { type: LfoType.Sine, frequency: 5, gain: 10 });
vibrato.connect(osc.frequency);

osc.connect(ac.destination);

Parameters

output = gen(phase) × gain + offset

| Param | Default | Range | Rate | Meaning | | ----------- | ------- | --------- | ------ | ----------------------------- | | type | 1 | 0 … 10 | k-rate | Waveform — see LfoType | | frequency | 10 | 0 … 200 | k-rate | Rate in Hz | | gain | 1 | 0 … 10000 | k-rate | Amplitude | | offset | 0 | ±1000 | k-rate | Where the waveform is centred |

LfoType is None (0), Sine (1), Triangle (2), RampUp (3), RampDown (4), Square (5), ExpRampUp (6), ExpRampDown (7), ExpTriangle (8), RandSampleHold (9) and Impulse (10).

All four parameters are k-rate — what is audio-rate here is the output, which is a different question. type is structural: swapping generator 128 times a block is not waveform modulation, it is noise. The other three are read once per block, which lets the generator hoist its phase increment out of the sample loop; a modulated frequency still moves, one step per render quantum. For an envelope on the depth, put a native GainNode between the LFO and its destination — that is a-rate and free.

Credits

concaveTransform is the MMA concave transform as presented by Will Pirkle (Tritone Systems) in Designing Software Synthesizer Plug-Ins in C++ and SynthLab, including the 5.0/12.0 correction coefficient.

See the repository's THIRD-PARTY-LICENSES.md.

License

MIT © danigb