GB532785A - Improvements in or relating to film sound records - Google Patents

Abstract

532,785. Optically recording and reproducing sound. ELECTRICAL RESEARCH PRODUCTS, Inc. Sept. 20, 1939, No. 26246. Convention date, Sept. 22, 1938. [Class 40 (ii)] In a sound recording system volume compression is applied during recording and the degree of compression is indicated by lateral displacement of the sound record, as shown in Fig. 4. Control of the recorded amplitude is effected either by manual means or electrically, using a rectified part of the microphone output. In each case a record of approximately constant amplitude is produced and a current, whose magnitude is proportional to the degree of compression, is passed to a solenoid to control the longitudinal displacement of a mask, Fig. 5 (not shown), which in turn causes lateral displacement of the recording light beam. The record produced is narrower than the usual sound track in order to accommodate this displacement. In the reproducer an optical wedge, in the form of a suitably graduated mask, is inserted in the light beam so that lateral displacement of the record with respect to this beam may cause a change in the intensity of the light passed to the light-sensitive cell and thus a change in the amplitude of the sound reproduced. For a variable area system of recording, the lateral displacement of the light beam should take place in steps.