Howl = function(o) {
    var self = this;

    // Throw an error if no source is provided.
    if (!o.src || o.src.length === 0) {
      console.error('An array of source files must be passed with any new Howl.');
      return;
    }

    self.init(o);
  }
Create an audio group controller.
@param {Object} o Passed in properties for this group.