The extra track in DiscJuggler, need a little help
 

When I open a Dreamcast cdi file in Discjuggler. it always tell me there are two tracks in it and that the first track is a audio file? What is this audio file for and can you leave it out? Has this file got something to do with self-booting games?

Hope someone can help me out, cause All the games that needs DJ has this frist audio file!