GB485469A - Improvements in and relating to the production of sound films - Google Patents

Abstract

485,469. Optical sound recording. KOLB, O. K. Nov. 19, 1936, No. 31708. [Class 40 (ii)] [Also in Group XL] Multiple variable-area sound tracks are recorded on a film by means of two or more separate electro-optical modulating devices and a single optical system for throwing the light from the modulating devices on to the film. The tracks may be in phase, or pushpull, or bilateral, or stereophonic, and may be "noiseless." As shown in Fig. 1, two microphones 1, 2 receiving sound from a source (not shown) are connected by separate amplifiers 11, 21 to separate oscillographs 12, 22. Light from two separate sources pass through separate optical systems 15, 25 to the mirrors 14, 24 of the oscillographs, and from thence through separate prisms 16, 26. After this, the light passes through a slit 31 and a single optical system 4 to the film 5, where two stereophonic tracks 41, 42 are formed. A switch 6 is provided between the amplifiers and the oscillograph, so that amplifier 21 may be cut out of circuit, and both oscillographs connected to the amplifier 11 to produce two similar tracks. Alternatively, the switch may be arranged to connect both amplifiers in parallel and in correct phase to both oscillographs. In another form, Fig. 2, the prisms 17, 27 throwing the light beams from the oscillographs 12, 22 to the slit 31 can be adjusted laterally, so as to cover the whole sound track of the flm 5 by the beam from the oscillograph 12 only. The adjustment of the prisms is performed by a handle 7 which simultaneously opens a switch 61 to disconnect the oscillograph 22 and replaces a single triangle aperture 18 by a double-peak aperture 19 in the incoming light beam to the oscillograph 12. Biassing systems such as described in Specifications 377,675 and 339,610 may be employed.