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Auxiliary Multitrack Magnetic Sound Reproducer
By C. G. DAVIS and H. A. MANLEY
A four-track magnetic soundhead for reproducing CinemaScope films in theaters is described. The unit mounts readily between projector and upper film magazine and is film driven. To facilitate threading, the film sprocket is locked when the pressure pads are opened. A low natural-period Davis filtered drive insures high-quality film motion.
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HEN Twentieth Century-Fox began the CinemaScope program, the Westrex Corporation was requested to design a special multichannel magnetic soundhead which would reproduce the four striped magnetic tracks on the composite release print employed in the CinemaScope presentation. The general requirements called for a unit, not to exceed 5 in. in height, to be mounted between the top of the picture projector and the upper magazine, capable of being installed with a minimum of effort. A 28-frame separation between picture and sound start marks was specified and provision was to be made in the soundhead for adjusting the length of the film path to accommodate different projectors employing varying film path lengths.
The CinemaScope program appears to be the first to utilize commercially a composite multitrack sound and picture release print. Figure 1 illustrates such
Presented on October 6, 1953, at the Society's Convention at New York by John G. Frayne for the authors, G. G. Davis and H. A. Manley, Westrex Corp., 6601 Romaine St., Hollywood 38, Calif. (This paper was received Nov. 2, 1953.)
a print and shows the location and dimensions of the four tracks. Tracks 1, 2 and 3 provide the three-channel stereophonic sound, while the fourth track is for special sound effects to be reproduced in the auditorium. It will be noted that the sprocket holes have been reduced in both width and height. The reduction in the width of the holes makes additional space across the film available for the multiple sound tracks.
The Westrex Stereophonic Reproducer has been designed to reproduce the four tracks of a CinemaScope release print without materially affecting the normal operation of theater equipment with standard release prints. For operation with standard release prints the equipment in the auxiliary head is by-passed and the film is threaded over two rollers and into the projector.
In considering the design of a filmpulling mechanism to meet the requirements, past experience indicated that three factors required special consideration. The first of these factors was obviously the successful scanning of the relatively small magnetic tracks adjacent to the sprocket holes. The solution was found to be an optimum combination
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March 1954 Journal of the SMPTE Vol. 62