Dixieland is usually described as "heterophony", meaning the voices don't have to sync precisely.

I don't know why a genre that was so much fun to play, listen to or dance to died out so completely - it's now only preserved by antiquarians, there's nothing new in the idiom being produced. Why did that happen? (Jazz took over and went off in directions as far away from its folk roots as it could possibly get - you'd think there ought to have been a continuing role for the older idiom).