Instructions
Enter any Pokemon Center in any city on both systems running "Ruby" and "Emerald." The city selection does not matter.
Walk up the stairs located to the left of the Pokemon Center.
Speak to the woman behind the third desk; she asks you which room you would like to join out of the three options provided: Trade Center, Colosseum and Record Corner.
Answer "Record Corner," the third option on the list, to enter the record mixing room.
Sit in any of the four available seats. Once any number up to four players are seated, the records are automatically mixed. Once the records have finished mixing, you can leave the room.