498,146. Optical sound - recording. SCOPHONY, Ltd., and WIKKENHAUSER, G. July 20, 1937, No. 20057. [Class 40 (ii)] [Also in Group XL] In an arrangement in which a double sided sound record is produced on a film F by light from a source S modulated by being passed through an optical system including a cell A through which sound-modulated high-frequency waves are passed, the crests of the recorded waves are brought always near the outer edges of the record strip to reduce noise-level at low sound amplitudes by increasing the mean highfrequency output of the oscillator when the sound amplitude decreases, this control being obtained by rectified current derived from rectification of the sound oscillations.