Phonofilm is an optical variable density sound-on-film system developed by inventors Lee de Forest and Theodore Case in the early 1920s. In 1919 and 1920, de Forest, inventor of the audion tube, filed his first patents on a sound-on-film process, DeForest Phonofilm, which recorded sound directly onto film as parallel lines.
Phonofilm is an optical variable density sound-on-film system developed by inventors Lee de Forest and Theodore Case in the early 1920s. In 1919 and 1920, de Forest, inventor of the audion tube, filed his first patents on a sound-on-film process, DeForest Phonofilm, which recorded sound directly onto film as parallel lines.
Source: Wikipedia "Phonofilm" · CC BY-SA 4.0
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