freeverb.js

class Freeverb extends CompositeAudioNode {
    get wetGain () {
        return this._wet.gain;
    }
    get dryGain () {
        return this._dry.gain;
    }
    get roomSize() {
        return mergeParams(this._combFilters.map(comb => comb.resonance))
    }
    get dampening() {
        return mergeParams(this._combFilters.map(comb => comb.dampening))
    }

    constructor (audioCtx, options) {
        super(audioCtx, options);
        const {roomSize: resonance, dampening, wetGain, dryGain} = options;
        const sampleRate = 44100
        const COMB_FILTER_TUNINGS = [1557, 1617, 1491,  1422,  1277,  1356, 1188,  1116 ]
        .map(delayPerSecond => delayPerSecond / sampleRate)
        const ALLPASS_FREQUENCES = [225, 556, 441, 341]

        this._wet = audioCtx.createGain()
        this._wet.gain.setValueAtTime(wetGain, audioCtx.currentTime)
        this._dry = audioCtx.createGain()
        this._dry.gain.setValueAtTime(dryGain, audioCtx.currentTime)
        this._merger = audioCtx.createChannelMerger(2)
        this._splitter = audioCtx.createChannelSplitter(2)
      
        this._combFilters = COMB_FILTER_TUNINGS
        .map(delayTime => new LowpassCombFilter(audioCtx, {dampening, resonance, delayTime}))
        const combLeft = this._combFilters.slice(0,1)
        const combRight = this._combFilters.slice(7)
        this._allPassFilters = ALLPASS_FREQUENCES
        .map(frequency => new BiquadFilterNode(audioCtx, {type: 'allpass', frequency}))

        this._input.connect(this._wet).connect(this._splitter)
        this._input.connect(this._dry).connect(this._output)
        combLeft.forEach(comb => {
            this._splitter.connect(comb, 0).connect(this._merger, 0, 0)
        })
        combRight.forEach(comb => {
            this._splitter.connect(comb, 1).connect(this._merger, 0, 1)
        })

        this._merger
        .connect(this._allPassFilters[0])
        .connect(this._allPassFilters[1])
        .connect(this._allPassFilters[2])
        .connect(this._allPassFilters[3])
        .connect(this._output)
    }
  }