var loadSoundFile = function(url) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.responseType = 'arraybuffer';
    xhr.onload = function(e) {
      context.decodeAudioData(this.response,
      function(decodedArrayBuffer) {
        buffer = decodedArrayBuffer;
      }
    };
    xhr.send();
  }