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Twin-Drum Film-Drive Filter System for Magnetic Recorder-Reproducer
By CARL E. HITTLE
Use of two drums in tight-loop type of film-drive filter system solves the problem of film support in magnetic recorder-reproducer utilizing two separate magnetic head assemblies. Performance of filter system is analyzed.
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.ANY VALUABLE contributions have been made to the art of sound recording by the design of film-drive mechanisms and a wealth of engineering principles covering these endeavors can be found in literature.1 It might be considered, however, that many of the film-drive mechanisms described in the references were designed for specific applications using photographic film as the recording medium, and were not particularly suited for the magnetic type of medium. The theory of recording with the latter has established certain requirements for the film-drive mechanisms. These were met only with some degree of compromise with many of the other photographic-type drives employed in what might be referred to as the interim period for the acceptance of magnetic recording by the motion picture industry. Magnetic recording, having proven to be a useful tool, has dictated the need for a more comprehensive design of the overall equipment as well as of the
Presented on October 18, 1951, at the Society's Convention at Hollywood, by Carl E. Hittle, Radio Corporation of America, Engineering Products Dept., RCA Victor Div., 1560 N. Vine St., Hollywood 28, Calif.
system components. The purpose of this paper therefore is to describe a film-drive mechanism especially designed for magnetic recording and one which makes use of the many advantages attributed to the magnetic medium.
Features of the film-drive mechanism especially designed for magnetic recording may be more fully appreciated when illustrated against a background of those of the basically photographic types which were converted for use of magnetic film.
The conversion of a photographictype recorder to magnetic is shown schematically in Fig. 1. In this instance, the photographic-type sound drum was foreshortened so that the portion of the magnetic film from the sound track location to the nearest outside edge of the magnetic film would extend beyond the drum much in the same fashion as would be required for converting to photographic sound reproducing. The single magnetic head was mounted so that the recording gap portion of the head would contact the coated surface of the magnetic film at the required location. The film-drive filter system of this recorder was a tightloop system utilizing a magnetic drive
April 1952 Journal of the SMPTE Vol. 58
323