WebAHDSR

An envelope generator for WebAudio AudioParam.

Installation

Include src/web-ahdsr.js in your HTML document:

<script type="text/javascript" src="<path-to-web-ahdsr>/src/web-ahdsr.js"></script>

Usage:

WebAHDSR requires an AudioContext and an AudioParam to control. The following example demonstrates how to control the volume (gain) of an oscillator:

// Create an AudioContext:
var context = null;
if (typeof window.AudioContext != 'undefined') {
	context = new AudioContext();
} else if (typeof window.webkitAudioContext != 'undefined') {
	context = new webkitAudioContext();
}

if (!context) {
	console.log('Web Audio API is not supported.');
	return;
}

// Create an oscillator:
var osc = context.createOscillator();
osc.type = 'sine';
osc.frequency.value = 440.0;

// Create a gain node:
var gainNode = context.createGain();
gainNode.gain.value = 0.0;

// Connect the oscillator to the gain node and start it:
osc.connect(gainNode);
osc.start(0);

// Connect the gain node to the context's destination (output):
gainNode.connect(context.destination);

// Create a WebAHDSR to control the gain node:
var gainAHDSR = new WebAHDSR(context, gainNode.gain);

// Configure the envelope times:
gainAHDSR.attackTime = 2.0;
gainAHDSR.holdTime = 1.0;
gainAHDSR.decayTime = 2.0;
gainAHDSR.releaseTime = 2.0;

// Configure the envelope values:
gainAHDSR.initialValue = 0.0; // Value before the attack period
gainAHDSR.holdValue = 1.0; // Value during the hold period (between attack and decay)
gainAHDSR.sustainValue = 0.3; // Value during the sustain period (between decay and release)
gainAHDSR.finalValue = 0.0; // Value after the release period

// Configure the envelope curves ('linear' or 'exponential'):
gainAHDSR.attackCurve = 'exponential';
gainAHDSR.decayCurve = 'exponential';
gainAHDSR.releaseCurve = 'exponential';

Start the attack-hold-decay-sustain period:

gainAHDSR.on();

Start the release period:

gainAHDSR.off();

Reset the envelope generator:

gainAHDSR.reset();

WebAHDSR can also be used to control the oscillator frequency:

// Create a WebAHDSR to control the oscillator frequency:
var freqAHDSR = new WebAHDSR(context, osc.frequency);

// Configure the envelope times:
freqAHDSR.attackTime = 0.5;
freqAHDSR.holdTime = 0.0;
freqAHDSR.decayTime = 0.5;
freqAHDSR.releaseTime = 0.0;

// Configure the envelope values:
freqAHDSR.initialValue = osc.frequency.value; // Begin at the oscillator's normal frequency
freqAHDSR.holdValue = osc.frequency.value * 2.0; // Ramp up one octave for the hold period
freqAHDSR.sustainValue = osc.frequency.value; // Sustain at the oscillator's normal frequency
freqAHDSR.finalValue = osc.frequency.value; // End at the oscillator's normal frequency

// Configure the envelope curves ('linear' or 'exponential'):
freqAHDSR.attackCurve = 'exponential';
freqAHDSR.decayCurve = 'exponential';
freqAHDSR.releaseCurve = 'exponential';

License:

WebAHDSR is made available under the MIT License. See LICENSE.txt for details.

Credits:

WebAHDSR was created by Tony Wallace.