GB373974A - Improvements in and relating to methods of and apparatus for photographic sound recording - Google Patents

Abstract

373,974. Optical sound - recording. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Kellogg, E. W.; 1185, Ardsley Road, Schenectady, New York, U.S.A.) Nov. 26, 1930, No. 35610. Convention date, Nov. 26, 1929. Void [Published under Sect. 91 of the Acts]. [Class 40 (ii).] In making a variable-width sound record, for example a record of sound received by a microphone 20, Fig. 1, and amplified by a valve amplifier 22 connected to a printing galvanometer 26, the weak sounds are over-amplified and simultaneously and automatically the printing light is dimmed, for example by means of a rheostat 28 in the circuit of the lamp 25 coupled to a volume control 32 on the amplifier, or by means of a " light wedge " in the path of the light. This gives a negative, Fig. 4, in which a weak sound 12 is recorded on the right-hand side of substantially the same amplitude as a strong sound on the left-hand side but having a greyish part 11 instead of the dead black on the left. In the positive, Fig. 5, the corresponding transparent part becomes partially opaque for the weak sounds on the right. When such a record is reproduced, the relative sound intensities are automatically reproduced, but the ground noise is reduced during the soft passages. A positive may be obtained directly by the known process of reversing or by an apparatus as in Fig. 6, in which the transparent part of the film is fogged by a separate lamp 36 controlled by the rheostat 28 or provided with a " light wedge " controlled by the rheostat. The amplifier 22 is provided with an independent volume control 31 in addition to the volume control 32 connected to the light control. If desired, the regulation of the amplitude and amount of light may be performed automatically by means responsive to the volume of the sound. Variable-density records may be similarly produced with automatically varied density ratios.