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The Movietone sound system is an optical sound-on-film method of recording sound for motion pictures that guarantees 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 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 being DeForest Phonofilm, Warner Brothers' Vitaphone, and RCA Photophone, though Phonofilm was principally an early version of Movietone.
As a student, Theodore Case became interested in the use of modulated light to carry speech, and in 1916 set up a laboratory to study the photo-electric properties of materials. He developed the Thalofide cell, a sensitive photocell, which was used as part of an infrared communication system by the U.S. Navy during, and for some years after WW1.
In 1922 Case and his assistant Earl I. Sponable turned their attention to "talking pictures". In that same year Case was approached by Lee de Forest who had been attempting since 1919 to create an optical soundtrack for motion picture film in a system he called Phonofilm . De Forest was having little success and turned to Case for help, so from 1922 until 1925 Case and de Forest collaborated in the development of the Phonofilm system. Amongst other Case inventions Case contributed the Thalofide photocell and also the Aeo-light, a light source that could be readily modulated by audio signals and was used to expose the soundtrack in sound cameras.
In 1925, however, Case ended his relationship with de Forest due to de Forest's tendency to claim the entire credit for the Phonofilm system for himself despite the fact that most of the critical inventions had come 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 the development of their own system, now called "Movietone".
From 1924 onwards Sponable had turned his attention to the design of single-system cameras, in which the sound and picture are recorded on the same negative. He asked Bell & Howell to modify one of their cameras to his design, but the results were unsatisfactory. Consequently, the Wall machine shop in Syracuse, New York was asked to rebuild this camera and the results were much improved.
Subsequently, many single-system 35mm cameras were produced by Wall Camera Corporation, which much later produced the three-film Cinerama cameras. Wall initially converted some Bell & Howell Design 2709 cameras to single-system, but most were Wall designed and produced. Single-system cameras were also produced by Mitchell Camera Corporation during World War II for the U.S. Army Signal Corps, although these cameras were quite rare.
Partly as a result of the single system experiments, the aspect ratio of approximately 1.19:1 that is created by printing an optical soundtrack on top of the 35mm full aperture became known colloquially as the "Movietone ratio". It was used extensively by Hollywood and European studios (apart from those that adopted sound-on-disc) between the late 1920s and May 1932, when the Academy ratio of 1.37:1 was introduced to restore the effective shape of the silent frame.
The 1950s brought the first 35mm kinescope camera with sound-on-film rather than separate, from Photo-Sonics, with a Davis Loop Drive mechanism built within the camera box. This camera was essential for TV network time-shifting in the years before Videotape. The sound galvanometer was made by RCA and was designed for good to excellent results when the kinescope negative was projected, thereby avoiding making a print before the delayed replay. The Davis mechanism was a Western Electric development.
After the split with de Forest, Case adopted a revised position for the projector soundhead, which was now placed below the picture head, with a sound-picture offset of 14+1⁄2 inches (370 mm) (which is close to the present day standard), rather than being placed above the picture head as had been the phonofilm practice. Case also adopted the 24 frames/sec speed for Movietone, bringing it in line with the speed already chosen for the Western Electric Vitaphone sound-on-disc system, and thus establishing 24 frames/sec as the standard speed for all sound films, whether sound-on-disc or sound-on-film. With a few exceptions, this has remained the standard speed for professional sound films ever since.  
At this point, the Movietone system was adopted by the AMPAS as the academy's standard. It and the later RCA Photophone system were interchangeable in most respects. See RCA Photophone for technical details and lists of the industry adopters.
Movietone entered commercial use when William Fox of the Fox Film Corporation bought the entire system including the patents in July 1926. Although Fox owned the Case patents, the work of Freeman Harrison Owens, and the American rights to the German Tri-Ergon patents, the Movietone sound film system uses only the inventions of Case Research Lab.
William Fox hired Earl I. Sponable (1895–1977) from Case Research Lab in 1926, when he purchased the sound-on-film patents from Case. The first feature film released using the Fox Movietone system was Sunrise: A Song of Two Humans (1927) directed by F. W. Murnau. It was the first professionally produced feature film with an optical sound track. The sound in the film included only music, sound effects, and very few unsynchronized words. The system was used for sound acting sequences in Mother Knows Best (1928).
Less than two years after purchasing the system from Case, Fox bought out all of Case's interests in the Fox-Case company. All of Fox's sound feature films were made using the Movietone system until 1931 when it was superseded by a Western Electric recording system using the light-valve invented by Edward C. Wente in 1923. However, Fox Movietone News used the system until 1939, because of the ease of transporting the single-system's sound film equipment.
The Case Research Lab sound system influenced many industry standards, such as positioning the optical sound 20 frames ahead of the image it accompanies.    The SMPTE standard for 35 mm sound film is +21 frames for optical, but a 46-foot theatre reduces this to +20 frames.   This was done partly to ensure the film runs smoothly past the sound head, but also to prevent Phonofilms from being played in theaters — as the Phonofilm system was incompatible with Case Research Lab specifications — and to ease the modification of projectors already widely in use.
Sponable worked at the Fox Film Corporation (later 20th Century Fox) Movietone studios on 54th Street and 10th Avenue in New York City until he retired in the 1960s, eventually winning an Academy Award for his technical work on the development of CinemaScope. Sponable made many contributions to film technology, including the invention of the perforated motion-picture screen that allowed placing the speakers behind it to enhance the illusion of the sound emanating directly from the film action. During his years at Fox, Sponable served for a time as an officer of the Society of Motion Picture and Television Engineers. He published a concise history of sound film in the April 1947 issue of The SMPE Journal (The SMPTE Journal after 1950). 
The history of Case Research Lab was long unheralded. Theodore Case died in 1944 and donated his home and laboratory to be preserved as a museum for the inventions of Case Research Lab. The museum's first director, who oversaw it for 50 years, put the laboratory's contents into storage and converted the building into an art studio. The Case Research Lab sound studio was located on the second floor of the estate's carriage house which was rented to a local model train club until the early 1990s.
Fox was seriously injured in a July 1929 car accident, lost his company in 1930 when his loans were called in, and lost the 1936 lawsuit in the U.S. Supreme Court against the film industry for violating his Tri-Ergon patents. Sponable did little to establish the record of Case Research Lab inventions, other than his April 1947 article in The Journal of the SMPE.
It was also in 1947 that the Davis Loop Drive was introduced to Western Electric licensees, including Twentieth Century-Fox (WECo RA-1231; still made by a successor company). [ citation needed ]
Case Research Lab, the adjoining carriage house, and Case's home have been restored and research is ongoing with the lab receipts, notebooks, correspondence, and much of the laboratory's original equipment, including the first recording device created to test the AEO light. The collections have letters from Thomas Edison, a copy of the Tri-Ergon patents, and an internal document from Fox Films written in the 1930s. This latter document says that once it became public knowledge that Sponable perfected the variable-area system of sound-on-film at the Fox Studios, that system became the standard and superseded the inventions of Case Research Lab.
A number of films owned by Case Research Lab and Museum were restored by George Eastman House in Rochester, New York, and are in their collections. The Case Research Lab and Museum has additional sound-film footage of Theodore Case, and recently discovered copies of the same films at the Eastman House, are in a much higher state of preservation. Movietone News films are in the collections of 20th-Century Fox and the University of South Carolina at Columbia, including the only known footage of Earl I. Sponable talking. Sponable can also be seen in footage of the premiere of the film The Robe .
Phonofilms that were produced using Case Research Lab inventions are in the collections of the Library of Congress and the British Film Institute.
The variable density (VD) recording systems developed from Movietone gradually lost market share to variable area (VA) systems developed from Photophone after the 1940s, a process that gathered pace as VA-related patents expired. Though both methods can theoretically achieve similar standards of recording, duplication and reproduction, quality control in the lab proved to be far more critical in the duplication of VD than VA tracks: slight errors in printer light settings and sensitometry and densitometry control will affect the signal-to-noise ratio of a VD track far more than a VA one. For this reason archives have tended to remaster original VD tracks to VA negatives for preservation and the creation of new prints.
35 mm film is a film gauge used in filmmaking, and the film standard. In motion pictures that record on film, 35 mm is the most commonly used gauge. The name of the gauge is not a direct measurement, and refers to the nominal width of the 35 mm format photographic film, which consists of strips 1.377 ± 0.001 inches (34.976 ± 0.025 mm) wide. The standard image exposure length on 35 mm for movies is four perforations per frame along both edges, which results in 16 frames per foot of film.
A sound film is a motion picture with synchronized sound, or sound technologically coupled to image, as opposed to a silent film. The first known public exhibition of projected sound films took place in Paris in 1900, but decades passed before sound motion pictures became commercially practical. Reliable synchronization was difficult to achieve with the early sound-on-disc systems, and amplification and recording quality were also inadequate. Innovations in sound-on-film led to the first commercial screening of short motion pictures using the technology, which took place in 1923.
Theodore Case Sound Test: Gus Visser and his Singing Duck, also known as Gus Visser and His Singing Duck, is a 1925 American short musical comedy film starring vaudeville performer Gus Visser. The short is an early sound film, directed by Theodore Case while perfecting his variable density sound-on-film process. Case began working on his sound film process at the Case Research Lab in Auburn, New York, in 1921.
A movie camera is a type of photographic camera that rapidly takes a sequence of photographs, either onto film stock or an image sensor, in order to produce a moving image to display on a screen. In contrast to the still camera, which captures a single image at a time, the movie camera takes a series of images by way of an intermittent mechanism or by electronic means; each image is a frame of film or video. The frames are projected through a movie projector or a video projector at a specific frame rate to show the moving picture. When projected at a high enough frame rate, the persistence of vision allows the eyes and brain of the viewer to merge the separate frames into a continuous moving picture.
Lee de Forest was an American inventor and a fundamentally important early pioneer in electronics. He invented the first practical electronic amplifier, the three-element "Audion" triode vacuum tube in 1906. This started the Electronic Age, and enabled the development of the electronic oscillator. These made radio broadcasting and long distance telephone lines possible, and led to the development of talking motion pictures, among countless other applications.
Vitaphone was a sound film system used for feature films and nearly 1,000 short subjects made by Warner Bros. and its sister studio First National from 1926 to 1931. Vitaphone was the last major analog sound-on-disc system and the only one that was widely used and commercially successful. The soundtrack was not printed on the film itself, but issued separately on phonograph records. The discs, recorded at 33+1⁄3 rpm and typically 16 inches (41 cm) in diameter, would be played on a turntable physically coupled to the projector motor while the film was being projected. It had a frequency response of 4300 Hz. Many early talkies, such as The Jazz Singer (1927), used the Vitaphone system. The name "Vitaphone" derived from the Latin and Greek words, respectively, for "living" and "sound".
A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. Modern movie projectors are specially built video projectors.
Sound-on-film is a class of sound film processes where the sound accompanying a picture is recorded on photographic film, usually, but not always, the same strip of film carrying the picture. Sound-on-film processes can either record an analog sound track or digital sound track, and may record the signal either optically or magnetically. Earlier technologies were sound-on-disc, meaning the film's soundtrack would be on a separate phonograph record.
Joseph Tykociński-Tykociner was a Polish engineer and a pioneer of sound-on-film technology.
Mitchell Camera Corporation was a motion picture camera manufacturing company established in Los Angeles in 1919. It was a primary supplier of newsreel and movie cameras for decades, until its closure in 1979.
RCA Photophone was the trade name given to one of four major competing technologies that emerged in the American film industry in the late 1920s for synchronizing electrically recorded audio to a motion picture image. RCA Photophone was an optical sound, "variable-area" film exposure system, in which the modulated area (width) corresponded to the waveform of the audio signal. The three other major technologies were the Warner Bros. Vitaphone sound-on-disc system, as well as two "variable-density" sound-on-film systems, Lee De Forest's Phonofilm, and Fox-Case's Movietone.
Phonofilm is an optical sound-on-film system developed by inventors Lee de Forest and Theodore Case in the early 1920s.
The Tri-Ergon sound-on-film system was developed from around 1919 by three German inventors, Josef Engl (1893–1942), Joseph Massolle (1889–1957), and Hans Vogt (1890–1979).
Photo-Kinema was a sound-on-disc system for motion pictures invented by Orlando Kellum.
Theodore Willard Case was an American chemist and inventor known for the invention of the Movietone sound-on-film system.
A film chain or film island is a television – professional video camera with one or more projectors aligned into the photographic lens of the camera. With two or more projectors a system of front-surface mirrors that can pop-up are used in a multiplexer. These mirrors switch different projectors into the camera lens. The camera could be fed live to air for broadcasting through a vision mixer or recorded to a VTR for post-production or later broadcast. In most TV use this has been replaced by a telecine.
Optical sound is a means of storing sound recordings on transparent film. Originally developed for military purposes, the technology first saw widespread use in the 1920s as a sound-on-film format for motion pictures. Optical sound eventually superseded all other sound film technologies until the advent of digital sound became the standard in cinema projection booths. Optical sound has also been used for multitrack recording and for creating effects in some musical synthesizers.
Auricon cameras were 16 mm film Single System sound-on-film motion picture cameras manufactured in the 1940s through the early 1980s. Auricon cameras are notable because they record sound directly onto an optical or magnetic track on the same film as the image is photographed on, thus eliminating the need for a separate audio recorder. The camera preceded ENG video cameras as the main AV tool of television news gathering due to its portability–and relatively quick production turn-around–where processed negative film image could be broadcast by electronically creating a positive image. Additionally, the Auricon found studio use as a 'kinescope' camera of live video off of a TV screen, but only on early pre-NTSC line-locked monochrome systems.
Finding His Voice (1929) is a short film, created as an instructional film on how the Western Electric sound-on-film recording system worked. Recording stars Billy Murray and Walter Scanlan, uncredited, provide the speaking and singing voices. Murray also provided the voice for the Fleischer Studios character Bimbo.
A sound follower, also referred to as separate magnetic, sepmag, magnetic film recorder, or mag dubber, is a device for the recording and playback of film sound that is recorded on magnetic film. This device is locked or synchronized with the motion picture film containing the picture. It operates like an analog reel-to-reel audio tape recording, but using film, not magnetic tape. The unit can be switched from manual control to sync control, where it will follow the film with picture.