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A clapperboard is a device used in filmmaking and video production to assist in the synchronizing of picture and sound, and to designate and mark particular scenes and takes recorded during a production. The sharp "clap" noise that the clapperboard makes can be identified easily on the audio track, and the shutting of the clapstick can be identified easily on the separate visual track. The two tracks can then be precisely synchronised by matching the sound and movement. Other names for the clapperboard include clapper, clapboard, slate, slate board, sync slate, time slate, sticks, board, and sound marker.
When a movie's sound and picture are out of synchronization, this is known as lip flap.
The clapperboard, clapboard slate or film slate is the combination of the chalkboard slate that held information identifying the next scene and the clapstick which was used to align sound and picture. In the early days of film, one person would hold a slate for the camera with the scene information, while another clapped two hinged sticks together in front of the camera. The combination of the two into one unit made it possible for one person to perform both tasks.
Traditional clapperboards consisted of a wooden slate and a hinged clapstick attached to the top of the slate. Modern clapperboards generally use a pair of wooden sticks atop whiteboard or translucent acrylic glass slates which do not require additional lighting from the camera side to be legible. Some versions are also backlit. Smart slates or digislates are electronic SMPTE time code versions with LED numbers. The clapsticks traditionally have diagonally interleaved lines of black and white to ensure a clear visual of the clap in most lighting conditions. In recent years sticks with calibrated color stripes have become available. In some productions, particularly those created in the digital domain, electronically superimposed versions of a clapperboard have supplanted the real thing.
In use, the details of the next take are written on the slate of the clapperboard.
- American: scene number, camera angle and take number; e.g. scene 24, C, take 3;
- European: slate number, take number (with the letter of the camera shooting the slate if using multiple-camera setup); e.g. slate 256, take 3C.
Often the European system will also include the scene number; however, a separate continuity sheet that maps the slate number to the scene number, camera angle and take number may be used if the scene number is not included on the slate. This is generally not as great a concern with short films, however. The clapper loader (or 2nd AC) is generally responsible for the maintenance and operation of the clapperboard, while the script supervisor is responsible for determining which system will be used and what numbers a given take should have. While these are usually fairly obvious once a system has been agreed upon, the script supervisor is usually considered the final arbiter in the event of an unclear situation.
A verbal identification of the numbers, known either as "voice slate" or "announcement", occurs after sound has reached speed. At the same time or shortly thereafter, the camera will start running, and the clapperboard is then filmed briefly at the start of the take and the clapsticks are clapped sharply as soon as the camera has reached sync speed. Specific procedures vary depending on the nature of the production (documentary, television, feature, commercial, etc.) and the dominant camera assisting conventions of the region; therefore it is not possible to describe a definitive practice aside from the general principles. Occasionally, instead of preparing an actual slate, a voice slate will be announced (often by an actor in the scene) and then the actor will clap their hands together, to provide the sync mark.
Sometimes a tail slate or end slate is filmed at the end of a take, during which the clapperboard is held upside-down. This is done when the clapperboard was not captured at the start of the take due to the camera being set up for the shot in such a way that the board cannot be captured, for example when a specific focus or frame is set up and cannot be altered until the take is complete. A clapper board is generally used to identify all takes on a production, even takes that do not require synchronization, such as MOS takes. When a slate is used to mark an MOS take, the slate is held half open, with a hand blocking the sticks, or closed, with a hand over the sticks.
The clapper (two sticks hinged together) may have been invented by Frank Thring (father of actor Frank Thring), who was head of Efftee Studios in 1920s Melbourne, Australia. The clapboard with both the sticks and slate together was invented by Leon M. Leon (1903–1998) a pioneer sound engineer.
A Denecke clapperboard containing LED numbers and colored stripes on the sticks.
A traditional wooden slate clapperboard.
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