stop(time) {
    if (this.started) {
      var t = time || 0;
      var now = p5sound.audiocontext.currentTime;
      this.oscillator.stop(t + now);
      this.started = false;
    }
  }
Stop an oscillator. Accepts an optional parameter
 to determine how long (in seconds from now) until the
 oscillator stops.

 @method  stop
 @for p5.Oscillator
 @param  {Number} [secondsFromNow] Time, in seconds from now.