The sims 3 custom music

Hello,
I recently bought the sims 3, and heard that you could put your own music files in to the custom music folder to play your songs through the game. For some reason i cant play the music i put in the folder. I even deleted the other music that came with that folder and it still wont work. Does the music have to be a specific format? or is there anything else i can try? thanks :)