The technological development that most liberated the sound film, however, was the practice known variously as postsynchronization, rerecording, or dubbing, in which image and sound are printed on separate pieces of film so that they can be manipulated independently. Postsynchronization enabled filmmakers to edit images freely again. Because the overwhelming emphasis of the period from 1928 to 1931 had been on obtaining high-quality sound in production, however, the idea that the sound track could be modified after it was recorded took a while to catch on. Many motion-picture artists and technicians felt that sound should be reproduced in films exactly as it had originally been produced on the set; they believed that anything less than an absolute pairing of sound and image would confuse audiences.
For several years, both practice and ideology dictated that sound and image be recorded simultaneously, so that everything heard on the sound track would be seen on the screen and vice versa. A vocal minority of film artists nevertheless viewed this practice of synchronous, “naturalistic”sound recording as a threat to the cinema. In their 1928 manifesto “Sound and Image,” the Soviet directors Sergey Eisenstein, Vsevolod Pudovkin, and Grigory Aleksandrov denounced synchronous sound in favour of asynchronous, contrapuntal sound—sound that would counterpoint the images it accompanied to become another dynamic element in the montage process. Like the practical editing problem, the theoretical debate over the appropriate use of sound was eventually resolved by the practice of postsynchronization.
Postsynchronization seems to have first been used by the American director King Vidor for a sequence in which the hero is chased through Arkansas swamplands in the all-black musicalHallelujah (1929). Vidor shot the action on location without sound, using a freely moving camera. Later, in the studio, he added to the film a separately recorded sound track containing both naturalistic and impressionistic effects. In the following year Lewis Milestone’s All Quiet on the Western Front and G.W. Pabst’s Westfront 1918 both used postsynchronization for their battle scenes. Ernst Lubitsch used dubbing in his first American sound films, the dynamic musicals The Love Parade(1929) and Monte Carlo (1930), as did the French director René Clair in Sous les toits de Paris (Under the Roofs of Paris, 1930). In all these early instances, sound was recorded and rerecorded on a single track, although some American directors, including Milestone and the Russian-born ArmenianRouben Mamoulian (Applause, 1929; City Streets, 1931), had experimented with multiple microphone setups and overlapping dialogue as early as 1929. Generally, through 1932, either dialogue or music dominated the sound track unless they had been simultaneously recorded on the set. In 1933, however, technology was introduced that allowed filmmakers to mix separately recorded tracks for background music, sound effects, and synchronized dialogue at the dubbing stage. By the late 1930s, postsynchronization and multiple-channel mixing had become standard industry procedure.