Web Audio APIを少し触ってみたコード片

demo.coffee

$ () ->
  ctx = document.getElementById("demo").getContext("2d")
  ctx.strokeStyle = "#000"
  ctx.fillStyle   = "#000"
  for x in [0..8]
    ctx.strokeRect x*80,0,80,280
  for x in [60,140,300,380,460]
    ctx.fillRect x,0,40,170
  player = new Simulator()
  $("#play").click () ->
    player.play($("#Hz option:selected").val(),0.2)

fmsim.coffee

class Simulator
  constructor: () ->
    @context = new webkitAudioContext()
    @context.sampleRate = @sampleRate
  
  sampleRate: 48000
  note: [
    262 #C3
    #277 #CS3
    294 #D3
    #311 #DS3
    330 #E3
    349 #F3
    #370 #FS3
    392 #G3
    #415 #GS3
    440 #A4
    495 #B4
    522 #C4
  ]

  play: (key,vol) ->
    buffer = @make(@note[key],vol)
    @src = @context.createBufferSource()
    @src.buffer = buffer
    @src.connect(@context.destination)
    @src.noteOn(0)

  stop: () ->
    @src.noteOff()

  make: (hz,vol) ->
    buffer = @context.createBuffer(1, @sampleRate, @sampleRate)
    data = buffer.getChannelData 0
    t = @sampleRate / hz
    t_half = t / 2
    for i in [0..(data.length)]
      data[i] = Math.sin((2*Math.PI / t) * i)
      #if ((i%t)<t_half)
      #  data[i] = vol
      #else
      #  data[i] =  -1 *vol
    return buffer