Early sync device for sound and picture — used perforated tape control to keep film projector and audio playback mechanically locked.
The synchronization of sound and image was a mechanical problem in the early sound film years. The Parlograph solved it through a punch tape-controlled coupling system: the film projector and sound playback system were physically coupled — not electronically, but mechanically via gears and electromagnetic pawls. Where timecode-controlled systems operate today, holes in a paper strip kept the rotation of two independent machines synchronized.
The system worked like this: The Parlograph read the punch tape during projection. If sound and image drifted apart — which constantly happened with mechanical transmissions — a braking device corrected the projector's feed. For sound engineers, this meant the punch tape had to be precisely prepared and inserted. A torn strip interrupted production. Resynchronization via software didn't exist — the session was interrupted and rescheduled.
The Parlograph was a transitional technology of the 1930s and early 1940s. Later, it was replaced by electronic synchronization systems based on control tones — more reliable and requiring less maintenance. The Parlograph shows how sound film professionals used mechanical engineering to solve a synchronization problem that algorithms handle today. The effort to physically synchronize two rotating machines was considerable — the Parlograph managed it.