A sane way to automate WebAudio parameters
npm install param-enveloper---
Hey look! A sane way to use parameters in WebAudio.
This is a small library for automating changes to an
AudioParam
(like a signal's gain or frequency).
It lets you schedule any series of ramps, sweeps, and delays, at arbitrary times,
_without_ causing discontinuities (i.e. audible clicks or glitches).
(That may not sound like much, but suffice to say that the
WebAudio API makes it difficult, and this library makes it easy.)
``ts
import { Enveloper } from 'param-enveloper'
const env = new Enveloper(myAudioContext)
// initialize a param, with starting value=0 since this is a gain node
const param = masterVolume.gain
env.initParam(param, 0)
// to play a note, first declare the time it starts:
env.startEnvelope(param, startTime)
// then schedule an AHDSR envelope - A/H/D are durations in seconds
env.addRamp(param, A, 1) // linear attack ramp to gain=1
env.addHold(param, H) // hold current gain
env.addRamp(param, D, 0.5, true) // exponential decay ramp to gain=0.5
// to schedule later changes like a release, start a new envelope
env.startEnvelope(param, releaseTime)
env.addSweep(param, -1, 0, 0.2) // -1 duration means open-ended sweep
// you can also query the scheduled param value at arbitrary times:
const val = env.getValueAtTime(param, ctx.currentTime + 0.5)
`
The special sauce here is that you can start a new envelope any time
(in response to user input, etc), and things will just work without causing
discontinuities, even if the new envelope starts during an ongoing ramp/sweep/etc.
Install via npm/yarn/bun:
`sh`
pnpm i --save param-enveloper # or npm/yarn/etc
`ts`
import { Enveloper } from 'param-enveloper'
var enveloper = new Enveloper(audioCtx)
enveloper.initParam(param, baseValue)
// ...
The API is documented in JSDoc comments; consult your local tooltip for details.
`ts
import { Enveloper } from 'param-enveloper'
class Enveloper {
constructor(ctx: AudioContext | OfflineAudioContext)
initParam(param: AudioParam, initialValue = 0)
startEnvelope(param: AudioParam, time = 0)
getValueAtTime(param: AudioParam, time: number)
addHold(param: AudioParam, duration: number)
addRamp(param: AudioParam, duration: number, target: number, exponential = false)
addSweep(param: AudioParam, duration: number, target: number, timeConstant: number)
}
`
To hack on this, use the local build / start` scripts. Contributions welcome!
---
Made with 🍺 by andy.
License is ISC.