In the thirties and forties, government-sponsored documentaries provided a forum for experimentation, in image and in sound, by such leading documentary filmmakers as Alberto Cavalcanti and Humphrey Jennings in Britain, and Pare Lorentz in America. Brazilian-born Cavalcanti worked in the French avant-garde in the twenties before moving to Britain in the early '30s. His experiments in sound were a primary contribution to the sound film in that era. In Pett and Pott (1934, 33 mins), a film made to encourage people to use the telephone, Cavalcanti recorded the soundtrack first and added images later. He used natural sounds, music and asynchronized sound to comic effect, with “a strong element of satire against middle class respectability and a whole air of grotesquerie that recalls Cavalcanti's earlier work in France.” In Coal Face (1935, 11 mins), though Cavalcanti's name does not appear on the credits, “the sound conception is all his own, and the film very obviously bears his stamp from start to finish...” The highly inventive soundtrack was intended as an experimental prelude to Night Mail (1936); in both, the rhythmic possibilities of words are explored, and sound is used, in Cavalcanti's words, to “extend the visual sense, rather than merely duplicate it.”
The Plow that Broke the Plains (1936, 29 mins) was the first film of critic Pare Lorentz, who went on to become the head of the U.S. film service in the Roosevelt Administration. The film, which dramatizes the problems of the dust bowl area of the Great Plains, is set in striking, expressive counterpoint to a now-classic score by Virgil Thomson that draws on traditional Midwestern themes.
Humphrey Jennings' Listen to Britain (made with Stewart McAllister, 1942, 20 mins) is a portrait of Britain at war that dispenses with commentary and relies on natural sounds and some music. “Jennings' complex editing, and his highly personal use of sound, adds...a dimension which is poetic rather than simply thematic... With the elimination of commentary the images...often acquire a rich ambiguity...” (quotations from British Film Institute catalogue)