GB406872A - Method and apparatus for sound recording and reproducing - Google Patents

Abstract

406,872. Optically recording and reproducing sound. RADIO CORPORATION OF AMERICA, 570, Lexington Avenue, New York, U.S.A. March 25, 1933, No. 9100. Convention date, May 9, 1932. [Class 40 (ii)]. F I G. 5. In photographic sound-recording' the undulations of the sound record trace which lie upon one side of the medium line thereof, and the undulations which lie on the opposite side of the said line, are recorded separately on tracks spaced apart from each other, the objects of the invention being to minimize background noise in reproduction, to improve high frequency response, and to enable a reproducing system to be used in which the exciter lamp may be fed with A.C. without the production of hum. A record such as is shown in Fig. 5 is made by an oscillograph apparatus, Fig. 3, which vibrates the shadow of a screen 25 to and fro along a slit in a fixed member 23, the shadow covering the slit completely when there is no vibration. This is shown in Fig. 4, in which 20 is the central patch of shadow in a vibratory light beam 18 which is reflected by the oscillograph mirror on to a slit 19. Another form of sound record, in which the separate component elements of the record are spaced from the edges of the sound track, is shown in Fig. 8. Such a record is made by the apparatus shown in Fig. 6, in which a " light stop " 34 having triangular openings 35, 36 is arranged between the lamp 38 and the mirror 41, corresponding images being produced, as shown, on opposite sides of the slit in a member 37. In reproducing sound from the record, by means of the apparatus shown in Fig. 9, the separate images of the positive and negative components of the record are focused respectively on two cathodes 52, 53 in a single photoelectric cell 46. The cell is connected as shown to the primary of a transformer 54.