Patent GB-417597-A (GB)
Title: Improvements in optical apparatus for reproducing sound from electro-mechanically-produced records
IPC: G11B7/135
Filed: 1933-03-29
Abstract: 417,597. Recording and reproducing sound. SOC. LA RECHERCHE INDUSTRIELLE FRANCAISE (R.I.F.) SOC. D'ETUDES POUR L'EXPLOITATION DES BREVETS NUBLAT, 5, Rue Galilee, Paris. March 29, 1933, No. 9473. Convention date, March 31, 1932. [Class 40 (ii).] Relates to photo-electric apparatus for reproducing sound from a record made in the form of a wavy groove of constant width and transparency ; such a record may be made by the removal, by means of a vibrating tool, of part of an opaque layer covering a transparent film, the width of the groove being such that each sinuous edge lies wholly on one side of a medial line. According to the invention, the reproducing apparatus comprises a diaphragm having a very narrow illuminated slit, and a short-focus objective forming an image of the slit transversely on the record in such a position (as shown at 6 or 7, Fig. 1) that the image is intersected by only one edge of the groove. As shown, one end of the image may lie on the medial line 4. The Specification as open to inspection under Sect. 91 includes also subject-matter now comprised in Specifications 417,644 and 417,645. It also describes a method of and apparatus for mechanically recording sound on a film comprising three layers, viz., a transparent base, a surface layer of opaque material, and an intermediate layer of soft transparent material. Various examples of suitable materials arc given. The recording tool is so arranged that its cutting edge penetrates slightly into the soft material without reaching the harder support. Fig. 4 (cancelled) shows the recording apparatus, in which the film 15 passes over a curved guide 16. At the place where the cutting tool 24 engages the film, the guide is formed with a portion 17, pressed upwardly by a counterweight 21 against a stop 22 which bears on the film and is attached by a spring 26 to the body 23 of the electromechanical receiver by which the cutter is vibrated transversely. The stop 22 coacts with a screw 25 to determine the depth of cut. By locating the screw at 27, the depth of cut may be automatically adjusted. The body 23 of the receiver is pivoted about an axis tangential to the film at the point where the cutter engages the film, so that the cutting edge is exactly parallel to the film. In order that several parallel sound tracks may be made on the film, the support to which the body 23 is pivoted is a slide which can be adjusted transversely of the film. A photo-electric device which is provided (as described in Specification 417,644) for enabling sound to be reproduced immediately after recording, is so mounted as to enable it to be moved across the film synchronously with the recording device. After recording, the sound grooves are covered by a thin layer of varnish 47, Fig. Sb (cancelled) which has the same index of refraction as the transparent base 48. By this means, defects due to minute serrations which may be caused by imperfections in the cutting edge are nullified. Processes are described for enabling copies of the grooved sound records to be printed in ink upon paper or the like. Sound reproduction may be effected from such copies either by means of reflected light, or by transmitted light when sufficiently thin paper is used. Alternatively, ultra-violet rays may be used, the paper being transparent to such rays, and the printing ink being such as to be opaque to them. This subject-matter does not appear in the Specification as accepted.