Classical Hollywood cinema
The beginning of the sound era itself is ambiguously defined. To some, it began with "The Jazz Singer", which was released in 1927 and increased box-office profits for films, as sound was introduced to feature films. To others, the era began in 1929, when the silent age had definitively ended. Most Hollywood pictures from the late 1920s to 1960s adhered closely to a genre—Western, slapstick comedy, musical, animated cartoon, and biopic (biographical picture)—and the same creative teams often worked on films made by the same studio. For instance, Cedric Gibbons and Herbert Stothart always worked on MGM films; Alfred Newman worked at Twentieth Century Fox for twenty years; Cecil B. DeMille's films were almost all made at Paramount Pictures; and director Henry King's films were mostly made for Twentieth Century Fox. Similarly, actors were mostly contract players. Film historians and critics note that it took about a decade for films to adapt to sound and return to the level of artistic quality of the silents, which it did in the late 1930s.
André Charlin
Charlin became involved in cinematography at a time when sound was starting to be added to motion pictures, and began to build equipment for synchronous sound playback.
At first this used 33 rpm records.
The first "talkies" appeared in 1931, and Charlin began working on ways to improve sound quality through better recording technology.
He founded a recording studio in 1933 that produced the sound tracks for many prewar movies, including in 1934 a stereo sound track for Abel Gance's 1927 silent movie "Napoléon".
He moved into techniques for film projection with a 1935 patent for "Cyclope" focussing and a 1938 patent for "Actua Colour" to project colour films which was used in over 1,000 movie theatres by 1948. 
During World War II he turned to making dynamos to power the lamps of bicycles.
In 1949 Charlin stopped producing cinema equipment and sold all his related patents to Philips of the Netherlands.
Early in the 1950s Radio-Cinema, a subsidiary of the Compagnie générale de la télégraphie sans fil, acquired Charlin' company.