web audio API FM echoes with reverb

fm.echo.verb.waapi.js

window.onload = function() {
  const gui = new dat.GUI()

  const ctx = new AudioContext()

  const delayLine = ctx.createDelay()
  delayLine.delayTime.value = .25

  const delayGain = ctx.createGain()
  delayGain.gain.value = .65

  delayLine.connect( ctx.destination )
  delayLine.connect( delayGain )
  delayGain.connect( delayLine )

  const reverb = ctx.createConvolver()
  reverb.connect( ctx.destination )

  const reverbInput = ctx.createGain()
  reverbInput.gain.value = 1
  reverbInput.connect( reverb )

  const glock = { cmRatio:3.5307, index: 1, attack:.001, decay:1 }

  fetch( './impulses/largeBrightPlate.wav' ).then(
    response => response.arrayBuffer()
  ).then( audioData => {
    ctx.decodeAudioData( audioData, buffer => {
      reverb.buffer = buffer
      const notes = [ 220, 440, 880, 1760 ]
      let noteCount = 0
      setInterval( ()=> {
        playNote( 
          notes[noteCount++ % notes.length], 
          glock.cmRatio, glock.index, glock.attack, glock.decay 
        ) 
      }, 500 )
    })
  })


  const props = {
    get 'delay time'() { return delayLine.delayTime.value },
    set 'delay time'( v ) { delayLine.delayTime.value = v },
    get feedback() { return delayGain.gain.value },
    set feedback( v ) { delayGain.gain.value = v },
    get 'reverb amount'() { return reverbInput.gain.value },
    set 'reverb amount'( v ) { reverbInput.gain.value = v }
  }

  gui.add( props, 'delay time', .0001, .5 )
  gui.add( props, 'feedback', .0, .99 )
  gui.add( props, 'reverb amount', 0, 2 )

  const playNote = function( frequency, cmRatio, index, attack, decay ) {	
    const carrier = ctx.createOscillator()
    carrier.frequency.value = frequency

    const mod = ctx.createOscillator()
    mod.frequency.value = frequency * cmRatio

    const modGain = ctx.createGain()
    modGain.gain.value = frequency * index

    mod.connect( modGain )
    modGain.connect( carrier.frequency )

    const envelope = ctx.createGain()
    carrier.connect( envelope )
    envelope.connect( ctx.destination )
    envelope.connect( delayLine )
    envelope.connect( reverbInput )

    envelope.gain.value = 0
    envelope.gain.linearRampToValueAtTime( .15, ctx.currentTime + attack )
    envelope.gain.linearRampToValueAtTime( 0, ctx.currentTime + attack + decay )	

    mod.start()
    carrier.start()

    carrier.stop( ctx.currentTime + attack + decay )
  }      
}