Sound was first printed onto film as microscopic lines
Before digital files, engineers turned sound into light, etching the roar of a crowd as a microscopic barcode along the edge of the frame.
In 1919, inventor Lee De Forest figured out how to photograph sound. His 'Phonofilm' system converted audio waves into electrical pulses that flickered a light bulb, exposing a tiny, 0.1-inch strip of film beside the pictures. This created a 'variable-density' soundtrack—a series of microscopic, horizontal lines of varying darkness. When the film ran through a projector, a light shone through these lines onto a sensor, which translated the changing shadows back into the voices of actors.
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