That is usually by the choice of the corps, as that is now controlled by each individual corps. A few years ago, they were given more flexibility as to how their corps is introduced, and if the PA announcer is on the field, just watch him and you will see a corps staff member standing next to him giving a cue when to make the announcements. If you watch closely, no two corps do it the same any more. The days of "Drum major, is your corps ready...wait for salute...you may take the field, etc. are gone.