feedback(f) {
    // if f is an audio node...
    if (f && typeof f !== 'number') {
      f.connect(this._leftGain.gain);
      f.connect(this._rightGain.gain);
    } else if (f >= 1.0) {
      throw new Error('Feedback value will force a positive feedback loop.');
    } else if (typeof f === 'number') {
      this._leftGain.gain.value = f;
      this._rightGain.gain.value = f;
    }

    // return value of feedback
    return this._leftGain.gain.value;
  }
Feedback occurs when Delay sends its signal back through its input
 in a loop. The feedback amount determines how much signal to send each
 time through the loop. A feedback greater than 1.0 is not desirable because
 it will increase the overall output each time through the loop,
 creating an infinite feedback loop. The default value is 0.5

 @method  feedback
 @for p5.Delay
 @param {Number|Object} feedback 0.0 to 1.0, or an object such as an
                                 Oscillator that can be used to
                                 modulate this param
 @returns {Number} Feedback value