GB358993A - Improvements in or relating to the recording and reproducing of sound - Google Patents

Abstract

358,993. 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. 17677. [Class 40 (ii).] Relates to the production of optical sound records of the variable width type, having a minimum of parasitic noise effect and operating by transmission, or reflection of light. To reduce ground noise the sound is recorded so that the crests of the waves of all amplitudes lie on a line of the record carrier which may be a longitudinal line or a line whose departures from a longitudinal line are less than the changes in amplitude of the sound being recorded, the changes in overall opacity of successive transverse strips of the record varying throughout in accordance with changes in the amplitude of the sound. Fig. 3 shows such a record with the crests of the low amplitude sounds recorded in the longitudinal lines containing the crests of greatest amplitude thereby reducing the areas which could produce parasitic noises due to dirt, scratches, &c. This record is produced by a beam directed past a ribbon 4 influenced by sound from a microphone 1, Fig. 1, and through a slit 8 on to a sensitive film 9, the ribbon extending through a magnetic field and being itself supplied with current from a battery 10 which current can be varied, when the connection FG is broken, by movement of a connection T over a resistance 11. Adjustment of the contact T by manual or automatic means when sounds of small amplitude are being recorded varies the central position of the ribbon 4 in relation to the slit 8 whereby the recorded crests of such sounds are displaced towards, or on to, a longitudinal line through the recorded crests of greatest amplitudes. The ribbon 4 may be replaced by two ribbons on a two-limbed ribbon, in which case the mean position of vibration must be controlled so that the slit is substantially completely uncovered once in each complete oscillation. The Provisional Specification describes also the production of constant width records of variable density.