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A clapperboard, also known as a dumb slate, clapboard, film clapper, film slate, bertolo clapz, movie slate, or production slate, is a device used in filmmaking, television production and video production to assist in synchronizing of picture and sound, and to designate and mark the various scenes and as they are filmed and audio-recorded. It is operated by the clapper loader. It is said to have been invented by Australian filmmaker F. W. Thring. Due to its ubiquity on film sets, the clapperboard is frequently featured in behind-the-scenes footage and films about filmmaking, and has become an enduring symbol of the film industry as a whole.
The clapper as two sticks hinged together is credited to F. W. Thring (father of actor Frank Thring), who later became head of Efftee Studios in Melbourne, Australia. The invention, however, is thought to be the responsibility of two of his sound engineers: Alan Mill and Harry Whiting. Oral citation by Jack Murray on Francis. R. (Director). (1992). Celluloid Heroes (Parts 1 & 2). A ‘new’ history of australian cinema, Tv Film Australia Productions. As mentioned on Fritzpatrick , P. (2012). p. 554. The clapperboard with both the sticks and slate together was a refinement of Leon M. Leon (1903–1998), a pioneer sound engineer.
The shutting of the clapper sticks is easily identified on the visual track, and the sharp "clap" noise is easily identified on the separate audio track. The two tracks can later be precisely synchronized by matching the sound and movement. Since each take is expressly identified on both the visual and audio tracks, segments of film are easily matched with corresponding segments of audio.
Methods were later developed to directly record sound to film as part of a single system integrated with the film camera (so-called single-system recording), which was most commonly used with small formats like Super 8 film. However, single-system recording did not render clapperboards obsolete. First, single-system recording of sound-on-film is "decidedly inferior in audio quality" to traditional double-system recording. Second, footage from single-system recording is difficult to shoot and edit. Since the Tape head cannot block the Movie projector gate and must be placed after the gate, the soundtrack must be offset by several frames (usually 28, 26, or 18 ahead) to maintain sync with the frame in the gate. With such footage, cutting to the next shot when an actor's lips stop moving will risk cutting off their last syllable, unless the soundtrack is copied and edited on a separate system, and actors must be directed to pause to allow for such cuts. Because of these technical limitations, the film industry has continued to use double-system recording for professional-quality film projects.
The development of videotape made single-system recording less inconvenient, since video and audio signals corresponding to the exact same point in time could now be captured and stored together as magnetic signals on the same medium. Despite that, contemporary digital cinematography still relies upon double-system recording, which means that directors of professional-quality film and television productions still need to use clapperboards. The main reason is that the audio features needed for quality single-system recording are found only on midrange or "prosumer" digital cameras. Low-end cameras omit those features for cost reasons. High-end professional cameras omit those features because manufacturers assume that a professional film crew will follow the well-established tradition of hiring a audio engineer (along with other sound specialists to form a sound department) who will bring along and use dedicated audio recording equipment.
A digislate is a clapperboard with an inbuilt electronic box displaying . The timecode displayed on the clapperboard will have been with the internal clock of the camera, so that in theory it should be easy for the film editor to pull the timecode metadata from the video file and sound clip and synchronize them together. When SMPTE timecodes actually work as intended, they relieve the film editor of the age-old chore of manually matching the exact frame in which the clapper sticks close to the "corresponding peak in the audio wave". This chore can be very "tedious" if "there is a large number of shots in a program". However, electronic timecodes can still drift during a long shooting day, so the clapper sticks on the clapperboard still need to be closed together in the traditional fashion, in order to ensure there is a way of manually synchronizing video and audio if matching the digital timecode fails.
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; its two sticks are snapped sharply together 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 Clapper loader regional conventions.
A clapperboard is generally used to identify all takes on a production, even takes that do not require synchronization, such as MOS takes, which have no sound. 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.
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