In the late 50’s Bob Gaudio had been picking up studio work as as keyboardist for producer Bob Crewe. Then Crew started to use the whole Four Seasons band working as session players and singers. One night Crewe decided to take in a four seasons performance at a local New Jersey club. It was that night, on a whim, Frankie Vallei started messing around on stage mimicking Jazz Singer, Rose Murphy’s High falsetto voice. 

It was just a goof. Crewe heard it said that’s it: That’s the sound.