@synthlet/param

A value with a unit: the module that makes numbers and nodes interchangeable

Part of Synthlet.

Param is a source node that carries one value — and because it is a node, it can carry a signal instead. That is the whole point: anywhere a Synthlet module takes a parameter, a number and a node are the same kind of thing, and Param is what makes that true.

On the way out it applies a conversion, a gain and an offset, so it is also where units get fixed: decibels into a linear gain, a 0…1 knob into a real range, a sign flip for an inverted modulation.

Install

npm i @synthlet/param

Or npm i synthlet for every module at once.

Usage

import { registerParamWorklet, Param, ParamScaleType } from "@synthlet/param";

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

// A number, modulated by a node
const cutoff = Param(ac, { input: 1200, mod: lfo, gain: 1 });
cutoff.connect(filter.frequency);

// Shortcuts for the common conversions
Param.db(ac, -6); //            decibels to a linear gain
Param.lin(ac, knob, 20, 20000); // a 0…1 input scaled to a range
Param.mul(ac, source, 0.5); //   scaling
Param.inv(ac, source); //        sign inversion
Param.input(ac, 440); //         a plain value

Parameters

output = offset + gain × convert(input + mod)

| Param | Default | Range | Rate | Meaning | | -------- | ------- | ------ | ------ | ------------------------------------------------------ | | input | 0 | ±20000 | a-rate | The signal | | mod | 0 | ±20000 | a-rate | A second signal, summed with input before conversion | | scale | 0 | 0 … 3 | k-rate | Which converter — see ParamScaleType | | min | 0 | ±20000 | k-rate | Bottom of Linear's range; ignored otherwise | | max | 1 | ±20000 | k-rate | Top of the same range | | gain | 1 | ±20000 | k-rate | Applied after the conversion | | offset | 0 | ±20000 | k-rate | Added last |

ParamScaleType is Bypass (0), DbToGain (1), GainToDb (2) or Linear (3).

The split is signal against coefficient. input and mod are what Param carries and are read per sample, so a gate edge or an LFO passes through with its timing intact. The other five describe what it does to them, are set once at construction by every factory above, and are read once per block. With nothing connected — or with a constant connected — the whole block still takes a fill() fast path, so an unautomated Param costs what it always did.

The ±20000 bounds are a safety limit, not a hint for a slider. Unlike a module's own parameters, a Param carries whatever its destination needs — a frequency in Hz, a level in dB, a time in seconds — and has no natural range of its own. scale is the exception; it is bounded by the enum.

License

MIT © danigb