work.suroh.tk/assets/js/synth.js

export class Synth {
  // SYNTH VOICE CONSTRUCTOR
  constructor(audio, type, env = {
    a: 0.2,
    r: 0.5,
  }) {

    this.audio = audio
    this.t = this.audio.currentTime

    this.env = {
      a: env.a,
      r: env.r,
    }

    // PRIMARY GAIN
    this.gain = this.audio.createGain()
    this.gain.gain.value = 0

    // PRIMARY VOICE
    this.primVoice = this.audio.createOscillator()
    this.primVoice.type = typeof type === 'string' ? type : 'sine'
    this.primVoice.connect(this.gain)
    this.primVoice.start()

    // MOD GAIN
    this.modGain = this.audio.createGain()
    this.modGain.gain.value = 0
    this.modGain.connect(this.gain)

    // MOD VOICE
    this.modVoice = this.audio.createOscillator()
    this.modVoice.type = 'triangle'
    this.modVoice.connect(this.modGain)
    this.modVoice.start()

  }

  // OSC -> ADSR -> GAIN
  noteOn(freq) {
    // note frequency
    this.freq = freq ? freq : (Math.random() * 350) + 150
    this.primVoice.frequency.setValueAtTime(this.freq, this.t)
    this.modVoice.frequency.setValueAtTime(this.freq - 20, this.t)
    // clear preScheduled events
    this.gain.gain.cancelScheduledValues(this.audio.currentTime)
    // attack
    this.gain.gain.setTargetAtTime(0.45, this.t + this.env.a, 0.2)
  }

  noteOff() {
    // release
    this.gain.gain.setTargetAtTime(0.0, this.t + this.env.r, 1)
  }

  mod() {
    this.modGain.gain.cancelScheduledValues(this.audio.currentTime)
    // attack
    this.modGain.gain.setTargetAtTime(0.8, this.audio.currentTime, 0.5)
    // release
    this.modGain.gain.setTargetAtTime(0.8, this.audio.currentTime + 0.4, 0.5)
  }
}