GB361907A - Improvements in and relating to sound recording apparatus - Google Patents

Abstract

361,907. Optical sound-recording apparatus. BRITISH THOMSON-HOUSTON Co., Ltd., Crown House, Aldwych, London.-(Assignees of Robinson, L. T. ; 100, Balltown Road, Schenectady, New York, U.S.A.) June 24, 1930, No. 19259. Convention date, June 24, 1929. [Class 40 (ii).] Comprises an apparatus for photographically recording sound in which the recording means is responsive to the alternating current corresponding to the wave form of the sound being recorded and is also influenced by a direct current responsive to the volume of the sound waves. As shown applied to a record of the variable width type, the optical system consists of a light source 7, Fig. 1, a condensing lens 8, a light stop 9, the mirror 10 of an oscillograph galvanometer 11, a cylindrical lens 12, a screen 13 having an aperture 14 and a lens 15, which serves to project a line of light 6 on to the film 1. Between the moving element 25 of the galvanometer and the amplifier 26 connected with the recording microphone is inserted a rectifying apparatus 27. This apparatus superimposes upon the sound-responsive current a rectified component thereof by means of contact rectifiers 28 .. 31. The connections include variable resistances 37, 38 and inductances 39, 40. Before use, the apparatus is adjusted so that the deflection due to the alternating current is substantially equal to the deflection caused by the rectified current, and the zero position is so adjusted that when no sound is being recorded the line 6 covers only a small portion of the sound track on the fi1m 1. In this manner, a positive sound film is obtained, as shown by Fig. 2, in which the axis of separation between the clear and opaque portions of the record is irregular and at varying distances from the boundarv line of the sound track in accordance with the volume of the recorded sound. For making a record of the variable-density type, a variable discharge lamp 45, Fig. 3, is used. The lamp 45 is illuminated partly by direct current from the battery 47 to which it is connected by the potentiometer 48 and partly by combined alternating and direct currents from the rectifying apparatus 27. The potentiometer is adjusted so that when there is no sound being recorded the illumination of the lamp 45 is so dim that the film 1 is substantially unexposed. During recording, the rectified current increases the illumination and this is modified by the alternating current corresponding to the wave form of the sound being recorded.