add(num) {
    var add = new Add(num);
    sigChain(this.mathOps, add, Add, this.oscillator, this.output);
    return this;
  }
Add a value to the p5.Oscillator's output amplitude,
 and return the oscillator. Calling this method again
 will override the initial add() with a new value.

 @method  add
 @for p5.Oscillator
 @param {Number} number Constant number to add
 @return {p5.Oscillator} Oscillator Returns this oscillator
                                    with scaled output