Sound Recording and Reproduction: "Sound on Film" 1943 Encyclopaedia Britannica Films - ERPI

more at http://quickfound.net/

HOW MICROPHONE TRANSFORMS KINETIC ENERGY OF AIR WAVES INTO ELECTRICAL ENERGY; HOW FLUCTUATIONS IN ELECTRIC CURRENT OPERATE PHOTOGRAPHIC LIGHT VALVE WHICH REGISTERS THEIR FLUCTUATIONS THRU VARYING LIGHT BEAM UPON SENSITIZED PHOTOGRAPHIC FILM; REVERSE. VARIABLE AREA & VARIABLE DENSITY SOUND TRACKS EXPLAINED & DEMONSTRATED. SOUND FILM PROJECTORS. 

Originally a public domain film from the Library of Congress Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Film

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

Film, also called movie or motion picture, is a medium used to simulate experiences that communicate ideas, stories, perceptions, feelings, beauty or atmosphere by the means of recorded or programmed moving images along with other sensory stimulations. The word "cinema", short for cinematography, is often used to refer to filmmaking and the film industry, and to the art form that is the result of it...

Traditionally, films were recorded onto celluloid film through a photochemical process and then shown through a movie projector onto a large screen... films recorded in a photochemical form traditionally included an analog optical soundtrack (a graphic recording of the spoken words, music and other sounds that accompany the images which runs along a portion of the film exclusively reserved for it, and is not projected)...

https://en.wikipedia.org/wiki/Single-system_recording

Single system audio is the system of recording sound on film or SOF. There are two methods of recording, the older method, optical and the later method, magnetic. SOF was primarily used for news film prior to the advent of portable videotape recording, but was used until recently for documentary film recording.

Optical

For Optical recording, the film only had a single perforation and the area where the other set of perforations would have been was exposed to a small bright lamp inside the camera controlled by an amplifier (usually in a separate box) that would vary the area of recording (RCA type), by means of shutters pulled back by variation in current, or variations in intensity (Western Electric type). Editing involved painting or taping over the optical track for the distance the sound led the film through the camera and projector. This would avoid the popping sound, but would result in a second of silence...