Tone has multiple types of envelopes for different purposes. Each of the envelopes implements an ADSR and all of the timings use tempo-relative Tone.Time stay synchronized with the tempo even as the bpm changes.

The attack portion of the envelope makes the output signal transition from 0 (min) to 1 (max) over the duration of the attack time.

When the peak value is reached, the envelope will fall to the sustain value over the duration of the decay time.

Unlike the other attributes of an ADSR envelope, sustain is not a time, but a percentage of the maximum value of the signal. It is a number between 0 and 1. The envelope will remain at the sustain value, until the release is triggered.

The time it takes for the envelope to return from the sustain value back to the minimum value is defined by the release time.

Play with the parameters of an AmplitudeEnvelope to hear how each of the phases effects the timbre of the input source.

example

The basic envelope type just outputs a signal in the range of 0-1. This node has only an output and no input.

triggerAttack starts the attack/decay portion of the envelope ending at the sustain value. An optional velocity argument will scale the output value at that number.

An amplitude envelope is just a Tone.Envelope connect to a GainNode so that audio passed into the input of the envelope will be scaled by the Tone.Envelope.

Tone.ScaledEnvelope has a range which starts at min and ramps to max. The min value can be larger than the max, it just represents what value the envelope starts at and ramps to.

The curve of the attack and release can be controlled by attackCurve and releaseCurve. These either take a string like "linear", "exponential", "sine", or an array of values to be used as the curve. Below are the curve names and their shapes.