adsr-gain-node/index.js

A simple and small nodejs module for creating an adsr gain node

function AdsrGainNode(ctx) {

    this.ctx = ctx;

    this.mode = 'exponentialRampToValueAtTime';
    // this.mode = 'linearRampToValueAtTime';

    this.options = {
        attackAmp: 0.1, 
        decayAmp: 0.3,
        sustainAmp: 0.7,
        releaseAmp: 0.01,
        attackTime: 0.1,
        decayTime: 0.2,
        sustainTime: 1.0, 
        releaseTime: 3.4,
        autoRelease: true
    };

    /**
     * Set options or use defaults
     * @param {object} options 
     */
    this.setOptions = function (options) {
        this.options = Object.assign(this.options, options);
    };

    this.gainNode
    this.audioTime
    
    /**
     * Get a gain node from defined options
     * @param {float} audioTime an audio context time stamp
     */
    this.getGainNode =  (audioTime) => {

        this.gainNode = this.ctx.createGain();
        this.audioTime = audioTime

        // Firefox does not like 0 -> therefor 0.0000001
        this.gainNode.gain.setValueAtTime(0.0000001, audioTime)        
        
        // Attack
        this.gainNode.gain[this.mode](
            this.options.attackAmp, 
            audioTime + this.options.attackTime)

        // Decay
        this.gainNode.gain[this.mode](
            this.options.decayAmp, 
            audioTime + this.options.attackTime + this.options.decayTime)

        // Sustain
        this.gainNode.gain[this.mode](
            this.options.sustainAmp, 
            audioTime + this.options.attackTime + this.options.sustainTime)
 
        // Check if auto-release
        // Then calculate when note should stop
        if (this.options.autoRelease) {
            this.gainNode.gain[this.mode](
                this.options.releaseAmp,
                audioTime + this.releaseTime()
            )
            
            // Disconnect the gain node 
            this.disconnect(audioTime + this.releaseTime())
        }
        return this.gainNode;
    };

    /**
     * Release the note dynamicaly
     * E.g. if your are making a keyboard, and you want the note
     * to be released according to current audio time + the ADSR release time 
     */
    this.releaseNow = () => {
        this.gainNode.gain[this.mode](
            this.options.releaseAmp,
            this.ctx.currentTime + this.options.releaseTime) 
        this.disconnect(this.options.releaseTime)
    }

    /**
     * Get release time according to the adsr release time
     */
    this.releaseTime = function() {
        return this.options.attackTime + this.options.decayTime + this.options.sustainTime + this.options.releaseTime
    }

    /**
     * Get release time according to 'now'
     */
    this.releaseTimeNow = function () {
        return this.ctx.currentTime + this.releaseTime()
    }
    
    /**
     * 
     * @param {float} disconnectTime the time when gainNode should disconnect 
     */
    this.disconnect = (disconnectTime) => {
        setTimeout( () => {
            this.gainNode.disconnect();
        },
        disconnectTime * 1000);
    };
}

module.exports = AdsrGainNode;