GB526567A - Improvements in or relating to sound recording - Google Patents

Abstract

526,567. Optical sound recording. RADIO CORPORATION OF AMERICA. March 20, 1939, No. 8875. Convention date, March 29, 1938. [Class 40 (ii)] A double density direct positive having little ground noise is made by projecting a narrow beam of light varied in accordance with the sound waves upon a film to expose an area defining the sound waves and projecting an additional beam varied in accordance with the envelope of the sound waves to fall on the filmwithin the said exposed area whereby to expose a portion of said area more densely than the remaining portions or margins of said area. Additional side beams to produce side exposures may also be used. As shown in Fig. 2, an aperture comprising a rectangular part 14A and a triangular part 13A is imaged by a soundoperated galvanometer on a plate 18 formed with two slits 21, 22. The slit 21 produces on the film a variable area record 27, Fig. 3, in the usual way. In conjunction with the slit 22, a shutter 19 is provided controlled by the envelope of the sound whereby inner and outer additional beams are controlled to produce the highly exposed parts 25, 26 on the film. In a modification, Fig. 4, the aperture has an inclined part 13B which produces a Class A push-pull sound record, and the shutter 19 has a flat centre part 30 which produces a continuous highly exposed centre part on the film. In another modification, the shutter is as in Fig. 4, but the aperture part co-operating with the slit 21 is N-shaped to produce a class B push-pull sound record. The records may be played directly ; or may be re-recorded as ordinary negatives from which prints can be made ; or negatives may be printed from the records and positives printed from the negatives ; or " reversal " positives may be printed by reversal from the records.