I hope this isn't necroing, as the OP is still active;
If the file is in your sounds folder, then in the map maker you need to type the name of the file with ".mp3" at the end.
The way to do it if you place the file in your music folder rather than sounds is more complicated and it is usually only used for putting multiple tracks in one map. Open music.cfg (located in the main FeralHeart folder) in Notepad, start a new line at the bottom, type whatever you want to call your music track/group of tracks in parentheses [] (like [insertmapnamehere]), and then, in a new line, type media/music/insertfilenamehere.mp3 and repeat for all the tracks you are using. When you are done, save then exit Notepad, and open FeralHeart. In the map maker type the name for the group of files. When you go to test the map, it should play them.
Hopefully this makes sense.
