I don’t know what it is called, but I can teach you how to set your favorite music as background music: Sonic background music replacement: First create two folders under the Sonic document and name them rnr_sound2 and rnr_sound3, step 2, we open the rnr_sound2 file and install our favorite music in it. It only supports MP3 format, otherwise it will not work. rnr_sound2 contains background music for chat rooms and single-player modes. Put the name of the MP3 Change them to chatroom and singleroom respectively. Okay, rnr_sound2 is set up. Now open the folder of rnr_sound3. Just like rnr_sound2, put in 3 MP3s you like, and then rename them to title lobby multiroom. Then that's it, the replacement is successful.