GB477952A - Improvements in or relating to sound film recording systems - Google Patents

Abstract

477,952. Optical sound recording apparatus. BRITISH OZAPHANE, Ltd., and WENDER, E. J. July 2, 1936, No. 18430. [Class 40 (ii)] [Also in Group XL] A so-called " noiseless " variable-area soundrecord is made by projecting upon a film a pair of light strips in the same straight line at right angles to the direction of movement of the film, the inner edges of the light strips extending parallel to the direction of motion of the film and being spaced apart so as to constitute two cutting or recording edges, said strips being moved similarly and simultaneously in opposite directions towards or away from one another in accordance with sound to be recorded and in accordance also with the mean strength or envelope of sound to be recorded. As shown in Fig. 1, light from a source 1 passes through an aperture 2 in a mask 3 and through a lens 4 to the mirror 5 of an oscillograph 7, and after this is split into two by a set of prisms 6 and thrown through a slit 12 in a plate 13 on to a film 11. The two beams of light are as shown at a<1> and a2, Fig. 3, when they strike the plate 13 having the slit 12. The oscillograph 7 is fed in a known way with sound control from amplifier 9 and envelope control from rectifieramplifier 10, themselves fed by a microphone 8. In a modification, Fig. 2, the oscillograph has two separate mirrors 5a, 5b working in opposite directions to produce the two beams of light which are thrown on the film by an optical device 14. Alternatively, two separate oscillographs may be used, and each made responsive to a predetermined frequency range only.