code: function(id) {
        var self = this;
  
        if (typeof id === 'undefined') {
          var ids = [];
          for (var i=0; i<self._sounds.length; i++) {
            ids.push(self._sounds[i]._id);
          }
  
          return ids;
        } else {
          return [id];
        }
      }
docs: Get all ID's from the sounds pool.
  @param  {Number} id Only return one ID if one is passed.
  @return {Array}    Array of IDs.