Motion picture sound synchronization

Abstract

A system is described for digital, as opposed to the usual analog, recording of a sound track in synchronism with a visual image on a motion picture film and automatically reproducing the sound in synchronism with the visual image. In one embodiment of the invention, a camera employs a linear array of light-emitting diodes across the sound track to enter a digital representation of the sound on the same frame as the synchronous visual image. The digital, specifically binary, signals which excite the light-emitting diodes are produced by analog to digital conversion of samples of the sound waveform. The binary representations are entered into shift registers at a uniform rate, and read out to the light-emitting diodes in a burst during the film advance interval immediately following shutter closure, thereby entering on the film track an optical record of all the binary pulses derived from sound produced during the just concluded frame interval. A projector capable of presenting the film sound and visual image in synchronism employs a strip of photodetectors to detect the binary pulses and a digital to analog converter to recover the original sound. Other embodiments of the invention utilize a fiber optics array, an image tube with fiber optic faceplate, or a laser scanner to enter the binary pulses on the optical sound track.