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How do clapperboards help synchronize picture and sound?

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Director Steven Spielberg and camera operator Michael Chapman film next to a large mechanical shark on the set of the 1975 movie Jaws. — motion-picture technology Director Steven Spielberg holding the movie camera, assisted by camera operator Michael Chapman, during the filming of *Jaws* (1975).

In professional filmmaking, motion-picture sound is typically recorded using a double-system recording method, where the audio is captured on a separate device from the camera. Because the sound track and image remain physically distinct until postproduction, they must be synchronized during the editing process.

The clapperboard, or "clapstick," serves as a visual and auditory reference point to align these separate tracks. By snapping the wooden jaws of the clapper together within the camera's field of view, the production crew creates a distinct, simultaneous event: the visual image of the jaws closing and the sharp, audible "clack" recorded on the audio track. During editing, the technician can match the frame where the jaws meet with the corresponding sound spike on the audio waveform to ensure perfect synchronization.

Additionally, the clapperboard displays information such as the take number, which is also announced aurally, allowing editors to identify and organize footage efficiently. Modern productions may also use digital slates that utilize light-emitting diodes and audio links to achieve this same synchronization.1