Optical Control of Wave-Shape and Amplitude Characteristics in Variable-Density Recording

The use of the optical penumbra to obtain linear variable-intensity light-modulation has already been described. The present paper shows how to obtain non-linear penumbras having predetermined intensity-amplitude characteristics. By this means it is possible to compensate optically for non-linear relation between negative exposure and print transmission known to exist in the variable-density system. — Variable-density noise-reduction has been obtained by moving the penumbra vane at right angles to the optical axis in accordance with the volume of the original sound. If a fixed penumbra vane is placed close to the movable vane, it forms an optical end-stop which limits the deflection of the penumbra after it has reached a predetermined position. The optical characteristics of penumbras formed by two displaced vanes are also shown. — For a given amplitude of galvanometer-mirror vibration, the extent of the light-modulation is determined by the penumbra height at the recording slit. The penumbra height may be varied by moving the penumbra vane along the optical axis. Either compression or expansion of the sound volume obtained from a film record may be effected by causing the penumbra vane to move along the axis in accordance with the volume of the original sound. Such a system is described in detail. — A combined system is also described which permits both noise-reduction and compression to be obtained by the use of a single shutter and noise-reduction amplifier.

Print ISSN

0097-5834

Published

1939-12

Content type

Original Research

DOI

10.5594/J01260