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EZ Web Audio / Envelope

Class: Envelope ​

Defined in: envelope.ts:60

ADSR Envelope class for managing amplitude envelope scheduling.

The envelope controls how a sound's amplitude evolves over time:

  • Attack: Ramp from 0 to peak (1.0)
  • Decay: Ramp from peak to sustain level
  • Sustain: Hold at sustain level until release() called
  • Release: Exponential decay to silence

Supports clickless retriggering: when a note is retriggered while the envelope is still active, it picks up from the current value instead of jumping to zero, preventing audible clicks.

Example ​

typescript
const envelope = new Envelope({
  attackTime: 0.05,
  decayTime: 0.1,
  sustainLevel: 0.7,
  releaseTime: 0.3
})

// Apply on note start
envelope.applyTo(gainNode.gain, audioContext.currentTime)

// Release on note end
envelope.release(gainNode.gain, audioContext.currentTime)

Constructors ​

Constructor ​

new Envelope(options): Envelope

Defined in: envelope.ts:87

Creates a new Envelope with the specified ADSR parameters.

Parameters ​

options ​

EnvelopeOptions = {}

ADSR configuration options

Returns ​

Envelope

Properties ​

attackTime ​

readonly attackTime: number

Defined in: envelope.ts:62

Duration in seconds to ramp from 0 to peak (1.0)

decayTime ​

readonly decayTime: number

Defined in: envelope.ts:65

Duration in seconds to ramp from peak to sustain level

releaseTime ​

readonly releaseTime: number

Defined in: envelope.ts:71

Duration in seconds for release to silence

sustainLevel ​

readonly sustainLevel: number

Defined in: envelope.ts:68

Amplitude level (0-1) held during sustain phase

Accessors ​

isActive ​

Get Signature ​

get isActive(): boolean

Defined in: envelope.ts:97

Whether the envelope is currently active (between applyTo and release).

Returns ​

boolean

Methods ​

applyTo() ​

applyTo(gainParam, startTime): void

Defined in: envelope.ts:165

Applies the attack-decay-sustain phases to an AudioParam.

Schedules:

  1. setValueAtTime(startValue, startTime) - Start from current value (0 for first trigger)
  2. linearRampToValueAtTime(1, startTime + attackTime) - Attack to peak
  3. linearRampToValueAtTime(sustainLevel, startTime + attackTime + decayTime) - Decay to sustain

If retriggering (envelope already active), cancels scheduled values and starts the attack from the current estimated value to prevent clicks.

Parameters ​

gainParam ​

AudioParam

The AudioParam to schedule the envelope on (typically gainNode.gain)

startTime ​

number

The audio context time to start the envelope

Returns ​

void

estimateCurrentValue() ​

estimateCurrentValue(currentTime): number

Defined in: envelope.ts:110

Estimates the current envelope value at a given time.

Used for retriggering to determine where to pick up from. Returns 0 if envelope is not active.

Parameters ​

currentTime ​

number

The time to estimate the value at

Returns ​

number

The estimated envelope value (0-1)

release() ​

release(gainParam, startTime): void

Defined in: envelope.ts:213

Applies the release phase to an AudioParam.

Uses setTargetAtTime for smooth exponential decay to zero. The time constant is calculated as releaseTime/5, which gives approximately 99% completion within releaseTime seconds.

Parameters ​

gainParam ​

AudioParam

The AudioParam to schedule the release on

startTime ​

number

The audio context time to start the release phase

Returns ​

void