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A waveform monitor is a device that monitors television signals over time. It is used in all aspects of film and television, from production to troubleshooting to research and development. Waveform monitors have evolved to keep up with changes in television and camera technology.
A television receives video signals as a series of lines. The order of these lines and the way in which they are scanned is called a raster pattern. Each line is made up of tiny points of color, called pixels. In order for a television signal to come in clearly, the raster pattern used by the television must match that used by the transmitter.
Almost every aspect of a video signal can be measured and recorded using a waveform monitor. It can keep track of the vertical blinking interval (VBLANK). The VBLANK is the time difference between the last line of one raster image and the first line of the next one. If the VBLANK is too great, television viewers may notice their screen flickering.
The waveform monitor can also measure the overall brightness of the picture. This allows the transmission to stay uniform over time. Another uniformity issue that can be waveform monitored is color burst. This is the signal that keeps colors unchanged from frame to frame. The instrument can even be set to measure only specific raster lines.
Modern waveform monitors are made up of two different measuring devices, an oscilloscope and a vectorscope. The oscilloscope monitors the voltage of a signal as it varies over time. Then it plots the output on a two-dimensional graph, usually displayed on a separate screen.
When the device was first invented, a waveform monitor was just an oscilloscope used to monitor video signal. Modern waveform monitors have a built-in vectorscope as well. A vectorscope plots the relation between two signals over time. The addition of the vectorscope allows the waveform monitor to take more sophisticated readings.
Readings from waveform monitors have many applications for the film and television industries. On the set of a film or television show, they are used to make sure that all the cameras are calibrated the same. They make sure that the raster pattern stays the same as the video is transferred from the camera to other devices. Readings can also help editors correct color and brightness issues.
Readings from a waveform monitor are used by technicians to diagnose problems. They are checked by installers to make sure all equipment can maintain a uniform signal. They are even used in research and development to create more reliable television and camera equipment.