Photographic Characteristics of Sound Recording Film

The various methods and general principles involved in the recording of sound by photographic methods are too well known to require detailed description and discussion. The methods at present in use commercially may be divided broadly into two classes: (1) The variable density type, and (2) the variable width type. The former may be subdivided, with respect to the method used for obtaining the variable exposure, into (a) those using the “light valve,” and (b) those employing a “flashing lamp.” In variable width recording the film is moved at a uniform linear velocity past a slit, or an optical image thereof. By suitable means the transverse length of this slit image is so modulated that the exposed area varies in lateral dimensions giving a sound record of the so-called “saw tooth” type. 9t any point within the exposed area the exposure incident on the photographic material is constant, both factors of exposure, namely, intensity (I) and time (t), being constant. This statement requires some modification since with the film moving continuously in one direction past a slit of finite width and the boundary of the illuminated area moving in a direction perpendicular to that of the film there must be a narrow envelop in which the t factor of exposure varies to some extent.

Print ISSN

0097-5834

Published

1930-02

Content type

Original Research

DOI

10.5594/J14808