Note that this approach requires the mp3 to be within your application's sub-directory called songs. You can also use relative pathing for the /songs/BrokenAngel.mp3
part (../../ or something like that. But it takes your applications directory as base!
File appDir = new File(System.getProperty("user.dir"));
URI uri = new URI(appDir.toURI()+"/songs/BrokenAngel.mp3");
// just to check if the file exists
File file = new File(uri);
System.out.println(file.exists())
URL song1Url = uri.toURL();