The classical French organ usually has two tremulants, the "Tremblant douce" and "Tremblant fort"
The Tremblant fort, or named Tremblant á vent perdu (German "Auslass-Tremulant") is rarely used since the 17th century, but was essential for the Grand Jeu, due to the still more dramatic effect and and perhaps the covering of more or less out of tune reed stops.
The Tremblant fort produces a strong noise due to the flap mechanism, which can be heard at the beginning of the music.
The Tremblant fort today is now largely out of service, for example today with the Silbermann organ of Ebersrmunster and so is often unknown, which is a pity.
The Riepp Dreifaltigkeits organ still has this tremulant active and I'm happy to present this unusual sound effect