index.html

<script>
function lalaj() {
  var out = document.querySelector("pre");
  var a = new OfflineAudioContext(1, 44100, 44100);
  var b = a.createBuffer(1, 44100, 44100);
  var g = a.createGain();
  var bb = b.getChannelData(0);
  for (var i = 0; i < bb.length; i++) {
    bb[i] = 1.0;
  }


  g.gain.setValueAtTime(0.0, 0.0);

  var curve = new Float32Array([-1, 0, 1]);

  g.gain.setValueCurveAtTime(curve, 0.7, 0.3);


  var source = a.createBufferSource();
  source.buffer = b;

  source.start(0);

  source.connect(g);
  g.connect(a.destination);

  a.oncomplete = function(e) {
    var buf = e.renderedBuffer.getChannelData(0);
    var endindex = Math.floor(0.95 * 44100);
    var startindex = Math.floor(0.65 * 44100);
    alert(endindex - startindex);
    var lala = "";
    for (var i = startindex; i < endindex; i++) {
       lala += (i / 44100) + ": " + buf[i] + "<br>";
    }

    out.innerHTML = lala;
  }

  a.startRendering()

}

window.onload = lalaj;

</script>

<pre>
</pre>