When activated, the music that plays in-game changes to match that of the original Pokémon Diamond and Pearl. Activating it again will revert the music back to the original soundtrack of the game. It also changes Pikachu and Eevee's cries; namely, it changes Pikachu's cry to the electronic noise used before Pokémon X and Y, and Eevee's to the one used from X and Y until Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!.
Like the GB Sounds, if the DS Sounds is hacked in before it would normally be obtained, music that would normally only play before that point (for instance, the music that plays during the event with DialgaBD/PalkiaSP) will still play the original versions.