Start a game and go to Angel Island Zone Act 1. Go to one of the swings that you hang from and grab on. While Sonic is swinging, press Left, Left, Left, Right, Right, Right, Up, Up, Up. You will hear a ring if you entered the code correctly. Pause the game and press A to take you back to the title screen. Press Down twice to find the newly unlocked Sound Test menu. Enter it, where you can play all of the sounds/music in the game and warp to any level.