amp(vol, rampTime = 0, tFromNow = 0) {
    if (typeof vol === 'number') {
      var now = p5sound.audiocontext.currentTime;
      this.output.gain.linearRampToValueAtTime(vol, now + tFromNow + rampTime);
    } else if (vol) {
      vol.connect(this.output.gain);
    } else {
      // return the Gain Node
      return this.output.gain;
    }
  }
Set the amplitude between 0 and 1.0. Or, pass in an object
 such as an oscillator to modulate amplitude with an audio signal.

 @method  amp
 @for p5.Oscillator
 @param  {Number|Object} vol between 0 and 1.0
                             or a modulating signal/oscillator
 @param {Number} [rampTime] create a fade that lasts rampTime
 @param {Number} [timeFromNow] schedule this event to happen
                               seconds from now
 @return  {AudioParam} gain  If no value is provided,
                             returns the Web Audio API
                             AudioParam that controls
                             this oscillator's
                             gain/amplitude/volume)