Ok, here's how it works: a professional orchestra audition is like the worst possible combination of March Madness and American Idol, except there are no cameras, and no one's doing anything to be funny or attract viewers.
Round 1: 95 trombonists show up. Maybe 10 make it out of this round, sometimes as few as three or four. This round is blind - the judges don't see who's auditioning, they're going totaly on sound.
Round 2: This round is optional - if 8 or 10 people make it through round one they'll hold a second round to cut down to three or four. This would also most likely be a blind round.
Final Round: This round they pull down the curtains and put the last few people through their paces. Sometimes they'll make you play with the rest of the orchestra's trombone section to see if you can keep up. Last one standing gets the job (not literally, but you get the idea).
OK - how far do you think I make it?