When taped sound must accompany the showing of a motion picture, problems of synchronization arise. This paper describes a simple, widely applicable regulator system for recording such sound, in which a high degree of synchronization is assured. As the film is run through the projector, the accompanying sound is taped on a half-track tape recorder. An auxiliary head simultaneously records a 60 cps tone derived from the projector power source upon the adjoining track. In playback, this tone, suitably amplified, drives a small auxiliary synchronous motor which, by appropriate gearing, controls the projector speed. Errors which may arise from stretched tape, tape creep, and line frequency variations are thus eliminated. Details of a typical system are presented, together with a description of the modifications which must be made on the tape recorder and the film projector.
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