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The Movietone sound system is an optical sound-on-film method of recording sound for motion pictures, ensuring synchronization between sound and picture. It achieves this by recording the sound as a variable-density optical track on the same strip of film that records the pictures. The initial version of this system was capable of a frequency response of 8500 Hz.
Although modern sound films use variable-area tracks instead, modern motion picture theaters (excluding those that have transitioned to digital cinema) can play a Movietone film without modification to the projector (though if the projector's sound unit has been fitted with red LED or laser light sources, the reproduction quality from a variable density track will be significantly impaired).
Movietone was one of four motion picture sound systems under development in the U.S. during the 1920s. The others were DeForest's Phonofilm, Warner Brothers' Vitaphone, and RCA Photophone. However, Phonofilm was principally an early version of Movietone.
In 1916, Theodore Case established a laboratory to research the photoelectric properties of materials. As a student, he developed an interest in using modulated light to record sound. He created the Thalofide cell, a sensitive photocell which was utilized by the U.S. Navy during and for some years after World War I as part of an infrared communication system.
In 1922, Case and his assistant, Earl I. Sponable, shifted their focus to talking pictures. During that year, Case was approached by Lee de Forest, who had been trying since 1919 to develop an optical soundtrack for motion picture film in a system he called Phonofilm. De Forest was not having much success and sought help from Case.
From 1922 to 1925, Case and de Forest collaborated in developing the Phonofilm system. Among Case's other inventions, he contributed the Thalofide photocell and the Aeo-light, a light source that could be easily modulated by audio signals and could finally be utilized to expose the soundtrack in the film of sound cameras.
In 1925, Case terminated his partnership with de Forest due to de Forest's habit of claiming sole credit for the Phonofilm system, despite most of critical inventions originating from Case. Documents supporting this, including a signed letter by De Forest that states that Phonofilms are only possible because of the inventions of Case Research Lab, are located at the Case Research Lab Museum in Auburn, New York.
In 1925, therefore, Case and Sponable continued developing their system, which they now called Movietone.
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Since 1924, Sponable focused on designing single-system cameras that could record both sound and pictures on the same negative. He requested Bell & Howell to modify one of their cameras according to his design, but the results were unsatisfactory. As a result, the Wall machine shop in Syracuse, New York was tasked with rebuilding this camera, and the results were significantly improved.
Subsequently, Wall Camera Corporation produced numerous single-system 35mm cameras, which eventually led to the later development of the three-film Cinerama widescreen cameras in the 1950s. Initially, Wall converted some Bell & Howell Design 2709 cameras to single-system, but most were designed and produced by Wall. Single-system cameras were also made by Mitchell Camera Corporation during World War II for the U.S. Army Signal Corps, although these cameras were relatively rare.
The aspect ratio of approximately 1.19:1 was introduced when single-system camera technology was developed. This technology printed an optical soundtrack on top of the 35mm full aperture, which was colloquially referred to as the Movietone ratio. This ratio was widely used by Hollywood and European studios (apart from those that adopted sound-on-disc) between the late 1920s and May 1932.
In May 1932, the Academy ratio of 1.37:1 was introduced, effectively restoring the original frame shape of the silent era.
In the 1950s, the first 35mm kinescope camera with sound-on-film was introduced by Photo-Sonics. This camera featured a Davis Loop Drive mechanism built within the camera box, which was essential for TV network time-shifting before the use of videotape. The sound galvanometer, made by RCA, was designed to produce good to excellent results when the kinescope film negative was projected, thereby avoiding the need to make a print before the delayed replay. Western Electric developed the Davis mechanism.
After parting ways with de Forest, Case made changes to the Movietone projector soundhead by positioning it below the picture head, with a sound-picture offset of approximately 370 mm (close to the present-day standard). This was a departure from the previous practice in Phonofilm, where the soundhead was placed above the picture head. Case also adopted the 24 frames/sec speed for Movietone, aligning it with the speed already chosen for the Western Electric Vitaphone sound-on-disc system. This established 24 frames/sec as the standard speed for all sound films, whether sound-on-disc or sound-on-film and has remained the standard speed for professional sound films with a few exceptions.
At this point, Case and Sponable's Movietone system was adopted by the AMPAS as the academy's standard. It was interchangeable with the later RCA Photophone system in most respects. For technical details and lists of the industry adopters, please refer to RCA Photophone.
The commercial use of Movietone began when William Fox of the Fox Film Corporation purchased the entire system, including the patents, in July 1926. Despite Fox owning the Case patents, the work of Freeman Harrison Owens, and the American rights to the German Tri-Ergon patents, the Movietone sound film system utilized only the inventions of Case Research Lab.
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