GB360903A - Improvements in or relating to the recording and reproducing of sound - Google Patents

Abstract

360,903. Recording sound optically. GRAMOPHONE CO., Ltd., Hayes, Middlesex, CONDLIFFE, G. E., Thorncombe, Fulmer Road, Gerrards Cross, Buckinghamshire, and BROWNE, C. O., 3, Freeland Road, Ealing Common, London. June 6, 1930, No. 27838/31. Divided on 358,993. [Class 40 (ii).] Optical sound records of the variable width type on opaque or transparent carriers and having a minimum of parasitic noise effect are so recorded that the crests and troughs of the recorded wave lie on longitudinal lines whose departure from straight lines is less than the changes in amplitude of the recorded sound and the transparency of the transparent part of the record varies in accordance with the changes in amplitude of the sound recorded, this variation of transparency being produced either at the recording stage or subsequently when making a positive from a negative. Fig. 1 shows a record in which the sound is recorded at constant and maximum amplitude, produced for example by the use of a microphone or microphones whose sensitivity is controlled in known manner so that the electrical impulses generated in them by the sound are all of approximately the same intensity. The transparent part of this record is made to vary in transparency in accordance with the variations in amplitude of the recorded sound, and this is effected either during the recording of the wavy line with constant and maximum amplitude, or in a printing operation from such wavy line record, by the adjustment manually or automatically of an optical wedge in the path or the recording light or of a printing light. Fig. 2 shows an arrangement for printing the desired record 13 from a wavy line record 9 of constant and maximum amplitude but whose transparent portions are not modulated. Light from a source 15 directed through a lens 16 and gate 14 prints the wavy line record 9 on to the carrier 13, and the transparent parts are modulated by a movable optical wedge 20 in the path of light from a source 18 directed through a lens 19, the wedge 20 and a gate 17 which need not be opposite to the gate 14. The movements of the wedge to effect modulation may be effected manually by the aid of a monitoring beam directed through the records at a point K and influencing a loud-speaker, and by providing the loud-speaker with a rheostat operatively connected with the wedge; adjustment of the rheostat to vary the speaker output as required will automatically adjust the wedge. The wedge may be calibrated.