There is no "booth," contrary to what you see in the FAQs. You sing for a "casting director," a cappella, anything you want (a "real" song, not something that hasn't been published). The casting director will give you some pointers -- I don't know if they do that if they don't want you at all, although I would presume they might -- my DS 16 tried out and the casting director suggested he be a little more animated, but passed him on to the next level. If you actually make it to the point where they're going to put you in a show, the producers will give you quite a few suggestions, and you get 10 minutes with a professional vocal coach who will work on song styling and movement. It can be really helpful, not just for the AI thing, but for anyone who likes to sing (my son is in theatre in school and lead singer for a band, so this was worthwhile for lots of reasons). Have fun and good luck!
Erin