code: function(id) {
        var self = this;
        var duration = self._duration;
  
        // If we pass an ID, get the sound and return the sprite length.
        var sound = self._soundById(id);
        if (sound) {
          duration = self._sprite[sound._sprite][1] / 1000;
        }
  
        return duration;
      }
docs: Get the duration of this sound. Passing a sound id will return the sprite duration.
  @param  {Number} id The sound id to check. If none is passed, return full source duration.
  @return {Number} Audio duration in seconds.