setPath(p, callback) {
    var path = p5.prototype._checkFileFormats(p);
    this.url = path;
    this.load(callback);
  }
Reset the source for this SoundFile to a
 new path (URL).

 @method  setPath
 @for p5.SoundFile
 @param {String}   path     path to audio file
 @param {Function} callback Callback