GB519857A - Improvements in and relating to the production of sound records - Google Patents

Abstract

519,857. Optical sound recording. RADIO CORPORATION OF AMERICA. Oct. 4, 1938, No. 28802. Convention date, Oct. 9, 1937. [Class 40 (ii)] Variable-area noiseless sound records are produced by first making a direct positive noiseless record, rerecording therefrom a noiseless negative, and printing release prints from said negative. The noiseless direct positive record may be made in various ways. As shown in Fig. 1, an image of an aperture plate 32 in the light path from a lamp 30 to a galvanometer mirror 35 is, reflected on a slit member 38, and the light going through this is thrown by lenses 39, 40 on a film 41. The aperture in the plate 32 may be of the N-shape shown at 49, Fig. 2, or at 55, Fig. 4, producing records as shown in Figs. 3 and 5 respectively, where the edges of the record are overdarkened by the wide ends of the slit 37. As shown in Fig. 6, the sound record is made on a film 70 by means of lamp 61, aperture plate 63, galvanometer mirror 65, slit plate 68, and objective 69 ; and in addition a noise reduction or envelope record is made by means of lamp 71, aperture plate 73, half-silvered galvanometer mirror 66, slit plate 68, and objective 69, the unsilvered part of mirror 66 allowing the light from mirror 65 to pass through. In a modification, the two mirrors are in separate paths, two separate slit plates and objectives are provided, and the noise reduction envelope is recorded in advance of the sound record. In another modification of this, a single objective is used, but a prism is inserted in the path of the noise reduction beam. In still another modification, a shutter device is used instead of the galvanometer mirror 66 for the noise reduction record. The sound recording aperture may be a triangle 79, Fig. 10, or an oblique slot 83, Fig. 15; the " noiseless " aperture may be a pair of rectangles 80, 81, Fig. 10, oscillating transversely, or a pair of angular slots 84, 85, Fig. 15, oscillating longitudinally; and the slit may be shown at 37 in these Figures. The records produced by these may be of the kind shown in Figs. 12, 13, 17 and 18. A suitable rerecording system is shown in Fig. 20, in which a photo-electric device comprising an anode 92 and two cathodes 93, 94 is intended to be illuminated by light modulated by a class A push-pull record in a known way. The output is supplied to the tapped primary of a transformer 95 through a resistance 96. The sound output is fed by the secondary of the transformer 95 to an amplifier 97. The noise reduction control is obtained from the resistance 96 by means of an amplifier 98 and a low-pass filter 99. Specifications 384,318 and 453,576, are referred to.