The music is not for the people to hear, neither it is part of the demonstration.It is for the pilots to help synchronize their maneuvers with the rhythm of said music.
Like using the drum or trumpet to help synchronize the movements of an XIX century army.
(If you find any mistake in my English, please let me know via a PM)
(Really, I speak terrible English, so please, tell me if I make mistakes. I'd like to improve it a bit )