Early sound film production encountered many challenges. Camera noise required each camera and operator to be placed in a soundproof booth or "sweat box." The dependence of sound-on-disc upon a level surface, temperature control, and a dust-free environment for the wax record gave sound-on-film an edge. Fox took Movietone outdoors for its first all-talking picture, In Old Arizona (1928). In 1930 the camera booth gave way to the "blimp," a wooden enclosure for the camera body, or to the "barney," a padded quilt. In 1928 microphones were concealed on the set in lamps, vases, flowerpots, candlestick telephones, or overhead light fixtures, another cause of camera stasis. But by 1929 microphones were suspended from booms, sometimes hitting actors in the head. Omni-directional microphones had to be kept close to the actors in order not to pick up unwanted sounds. Directors asked for microphones that could be aimed at the person actually speaking. Bidirectional microphones, and some that claimed to be unidirectional, appeared in the 1930s, with true unidirectional microphones offered in 1941.
When critics complain about the lack of camera mobility in early sound films, they are not talking just about literal movement (most shots in silent films were made from a tripod) but about the lost facility with which the scenes had been structured through camera angles with time compressed or expanded by editing. Sound pulled movies away from cinematic time and toward real time. Most scenes were shot with multiple cameras and a single audio recording. Warner's On Trial (1928) was derided for the long shot of the courtroom.
It was possible to edit sound-on-disc by means of interlocked turntables that could be cued to specific grooves, but that process was meant to assemble several scenes onto one disc, not shots within scenes. Sound-on-film had an obvious advantage in that it could be spliced. By 1932 most scenes were made with a single camera. The "master scene" would be filmed all the way through as in a play. The close-ups, reactions, and over-the-shoulder shots would then be filmed separately and miked accordingly. All studios (including Warner, which dropped sound-on-disc in March 1930) recorded a separate strip of film in a "sound camera." To cut sound apart from the picture, yet in sync with it, Moviola added a sound reader to its editing consoles in 1928. In the 1930s they could run two and three sound tracks.
"Rerecording," the combination of production and post-synchronized sound, steadily improved. King Kong (1933), with complex sound effects and speech at the same time, and a score that "catches" individual lines of dialogue, would have been impossible even eighteen months earlier. Rerecording put an end to the production of "foreign" versions as the dialogue could be dubbed with sound effects and music retained.
In 1947 a new recording medium became available: sprocketed film coated with magnetic iron oxide. It was estimated that by 1951, 75 percent of recording, editing, and mixing in Hollywood was done on magnetic track. Lightweight recorders such as the Nagra that used 1/4-inch magnetic tape with a "sync pulse" from the camera appeared in the 1950s and gained wide use in the 1960s. On the postproduction side, the early dubbing machinery used the old film transports retrofitted with magnetic heads. Because a gap or click could be heard where the recording stopped and resumed, films were still mixed the old way, that is, in 1,000-foot reels. A mistake lost all the work to that point. Advances in electronics in about 1969 enabled "backup," or "rock 'n' roll," where the new recording could be superimposed on the end of the old.
The wide-screen upheaval of the 1950s brought magnetic stereo into theaters. Cinema-Scope offered left, center, and right channels behind the screen and a "surround" channel in the auditorium from four stripes of magnetic oxide on the 35mm print. Todd-AO's six-track 70mm format (five speakers behind the screen plus surround) set the standard for deluxe presentations. In 1976, noise reduction technology made it possible to derive four-channel stereo from a pair of mono-compatible optical tracks, popularly known as "Dolby." The 1990s saw three types of digital sound: Dolby Digital and SDDS on the film itself and the disc-based DTS system.