adsr

Attack, decay, sustain, release envelope for automating Web Audio API AudioParams.

Install

$ npm install adsr

API

var ADSR = require('adsr')

ADSR(audioContext)

Returns an ADSR ModulatorNode instance.

node.attack (get/set)

Attack time in seconds.

node.decay (get/set)

Decay time in seconds.

node.sustain (get/set)

Decimal representing what multiple of initial value to hold at in sustain portion of envelope.

node.release (get/set)

Release time in seconds.

node.value (AudioParam)

The target value of the attack portion of envelope. Defaults to 1.

node.startValue (AudioParam)

The start value which will ramp to node.value over time specified by node.attack. Defaults to 0.

node.endValue (AudioParam)

The final value which will be ramped to over time specified by node.release. Defaults to 0.

node.connect(destinationAudioParam)

Connect the modulator to the desired destination audio param.

node.disconnect()

Disconnect from any target AudioParams and reset to node.value.

node.start(at)

Trigger the attack-decay-sustain portion of the envelope at the specified time relative to audioContext.currentTime.

This can only be called once. Create additional instances of ADSR for multiple events.

node.stop(at, isTarget)

Specify the time to start the release portion of the envelope. Or if isTarget === true, the time the release portion should complete by.

Returns the time that the release portion will complete by (this can be used to decide when to stop the source AudioNode)

Example

var audioContext = new AudioContext()
var oscillator = audioContext.createOscillator()
var gain = audioContext.createGain()
 
oscillator.connect(gain)
gain.connect(audioContext.destination)
 
var envelopeModulator = ADSR(audioContext)
 
gain.gain.value = 0 // set base value to 0 as modulators add to existing value
envelopeModulator.connect(gain.gain)
 
envelopeModulator.attack = 0.01 // seconds
envelopeModulator.decay = 0.4 // seconds
envelopeModulator.sustain = 0.6 // multiply gain.gain.value
envelopeModulator.release = 0.4 // seconds
 
envelopeModulator.value.value = 2 // value is an AudioParam
 
envelopeModulator.start(audioContext.currentTime)
oscillator.start(audioContext.currentTime)
 
var stopAt = envelopeModulator.stop(audioContext.currentTime + 1)
oscillator.stop(stopAt)