Film Recording

Author: N.H. Crowhurst

Film recording and film playback

Film recording is usually achieved photographically by producing an exposure on the film proportional to the instantaneous audio. This is accomplished by means of a light "valve" that controls the amount of light falling on the film as it passes by a slot. In playback, the same film, with the recording photographically reproduced on it, is scanned by means of a photoelectric cell, the output from which is amplified by an audio amplifier.

Because the photoelectric cell is sensitive to the quantity of light, the sound track on the film can vary either in the area through which light passes or in the transparency (density) of the film. Both methods have their uses, their advantages and disadvantages, which are concerned more with light and optics than with audio. As with the other methods of recording, special equalization is required on playback.

Methods of recording. Left: variable area, right: variable density