code: function(notes) {
    var _this = this;
  
    // last octave set
    this._octave = 4;
  
    notes = this._parseNotes(notes);
    return function(time, opts) {
      opts = _this._options(opts);
      var n = Math.floor((time * opts.tempo) % notes.length);
      return opts.volume * (Math.sin((2 * Math.PI) * notes[n] * time));
    };
  }
docs: class