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Genlock (generator locking) is a common technique where the video output of one source (or a specific reference signal from a signal generator) is used to synchronize other picture sources together. The aim in video applications is to ensure the coincidence of signals in time at a combining or switching point. When video instruments are synchronized in this way, they are said to be generator-locked, or genlocked. [1] [2] [3] [4] [ excessive citations ]
Video signals generated and output by generator-locked instruments are said to be syntonized. Syntonized video signals will be precisely frequency-locked, but because of delays caused by the unequal transmission path lengths, the synchronized signals will exhibit differing phases at various points in the television system. Modern video equipment such as production switchers that have multiple video inputs often include a variable delay on each input to compensate for the phase differences and time all the input signals to precise phase coincidence.
Where two or more video signals are combined or being switched between, the horizontal and vertical timing of the picture sources should be coincident with each other. If they are not, the picture will appear to jump when switching between the sources whilst the display device re-adjusts the horizontal and/or vertical scan to correctly reframe the image.
Where composite video is in use, the phase of the chrominance subcarrier of each source being combined or switched should also be coincident. This is to avoid changes in colour hue and/or saturation during a transition between sources.
Generator locking can be used to synchronize as few as two isolated sources (e.g., a television camera and a videotape machine feeding a vision mixer (production switcher)), or in a wider facility where all the video sources are locked to a single synchronizing pulse generator (e.g., a fast-paced sporting event featuring multiple cameras and recording devices). Generator locking can also be used to ensure that multiple CRT monitors that appear in a movie are flicker-free. Generator locking is also used to synchronize two cameras for Stereoscopic 3D video recording.
In broadcast systems, an analog generator-lock signal usually consists of vertical and horizontal synchronizing pulses together with chrominance phase reference in the form of colorburst. No picture information is usually carried to avoid disturbing the timing signals, and the name reference, black and burst , color black, or black burst is usually given to such a signal. A composite colour video signal inherently carries the same reference signals and can be used as a generator-locking signal, albeit at the risk of being disturbed by out-of-specification picture signals.
Although some high-definition broadcast systems may use a standard-definition reference signal as a generator-locking reference signal, the use of tri-level synchronising pulses directly related to the frame and line rate is increasing within HD systems. A tri-level sync pulse is a signal that initially goes from 0 volts DC to a negative voltage, then a positive voltage, before returning to zero volts DC again. The voltage excursions are typically 300 mV either side of zero volts, and the duration each of the two excursions is the same as a particular number of digital picture samples.
Most television studio and professional video cameras have dedicated generator-locking ports on the camera. If the camera is tethered with a triaxial cable or optical fibre cable, the analog generator-locking signal is used to lock the camera control unit, which in turn locks the camera head by means of information carried within a data channel transmitted along the cable. If the camera is an ENG-type camera, one without a triax/fibre connection or without a dockable head, the generator-locking signal is carried through a separate cable from the video.
Natlock is a picture-source synchronizing system using audio tone signals to describe the timing discrepancies between composite video signals, while Icelock uses digital information conveyed in the vertical blanking interval of a composite video signal.
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
NTSC is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170.
Colorburst is an analog and composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back porch (beginning) of each scan line, a television receiver is able to restore the suppressed carrier of the chrominance (color) signals, and in turn decode the color information. The most common use of colorburst is to genlock equipment together as a common reference with a vision mixer in a television studio using a multi-camera setup.
Composite video is an baseband analog video format that typically carries a 405, 525 or 625 line interlaced black and white or color signal, on a single channel, unlike the higher-quality S-Video and the even higher-quality YPbPr.
S-Video is an analog video signal format that carries standard-definition video, typically at 525 lines or 625 lines. It encodes video luma and chrominance on two separate channels, achieving higher image quality than composite video which encodes all video information on one channel. It also eliminates several types of visual defects such as dot crawl which commonly occur with composite video. Although it is improved over composite video, S-Video has lower color resolution than component video, which is encoded over three channels.
Component video is an analog video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) information that is transmitted or stored as three separate signals. Component video can be contrasted with composite video in which all the video information is combined into a single signal that is used in analog television. Like composite, component cables do not carry audio and are often paired with audio cables.
A clock generator is an electronic oscillator that produces a clock signal for use in synchronizing a circuit's operation. The signal can range from a simple symmetrical square wave to more complex arrangements. The basic parts that all clock generators share are a resonant circuit and an amplifier.
A waveform monitor is a special type of oscilloscope used in television production applications. It is typically used to measure and display the level, or voltage, of a video signal with respect to time.
A pulse generator is either an electronic circuit or a piece of electronic test equipment used to generate rectangular pulses. Pulse generators are used primarily for working with digital circuits; related function generators are used primarily for analog circuits.
A composite monitor or composite video monitor is any analog video display that receives input in the form of an analog composite video signal to a defined specification. A composite video signal encodes all information on a single conductor; a composite cable has a single live conductor plus earth. Other equipment with display functionality includes monitors with more advanced interfaces and connectors giving a better picture, including analog VGA, and digital DVI, HDMI, and DisplayPort; and television (TV) receivers which are self-contained, receiving and displaying video RF broadcasts received with an internal tuner. Video monitors are used for displaying computer output, closed-circuit television and other applications requiring a two-dimensional monochrome or colour image.
Time base correction (TBC) is a technique to reduce or eliminate errors caused by mechanical instability present in analog recordings on mechanical media. Without time base correction, a signal from a videotape recorder (VTR) or videocassette recorder (VCR), cannot be mixed with other, more time-stable devices such as character generators and video cameras found in television studios and post-production facilities.
A video signal generator is a type of signal generator which outputs predetermined video and/or television oscillation waveforms, and other signals used in the synchronization of television devices and to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses or sync words. Generators of composite video signals will also include a colorburst signal as part of the output.
A digital delay generator is a piece of electronic test equipment that provides precise delays for triggering, syncing, delaying, and gating events. These generators are used in many experiments, controls, and processes where electronic timing of a single event or multiple events to a standard timing reference is needed. The digital delay generator may initiate a sequence of events or be triggered by an event. What differentiates it from ordinary electronic timing is the synchronicity of its outputs to each other and the initiating event.
An oscilloscope is a type of electronic test instrument that graphically displays varying voltages of one or more signals as a function of time. Their main purpose is capturing information on electrical signals for debugging, analysis, or characterization. The displayed waveform can then be analyzed for properties such as amplitude, frequency, rise time, time interval, distortion, and others. Originally, calculation of these values required manually measuring the waveform against the scales built into the screen of the instrument. Modern digital instruments may calculate and display these properties directly.
The history of the oscilloscope was fundamental to science because an oscilloscope is a device for viewing waveform oscillations, as of electrical voltage or current, in order to measure frequency and other wave characteristics. This was important in developing electromagnetic theory. The first recordings of waveforms were with a galvanometer coupled to a mechanical drawing system dating from the second decade of the 19th century. The modern day digital oscilloscope is a consequence of multiple generations of development of the oscillograph, cathode-ray tubes, analog oscilloscopes, and digital electronics.
White Rabbit is the name of a collaborative project including CERN, GSI Helmholtz Centre for Heavy Ion Research and other partners from universities and industry to develop a fully deterministic Ethernet-based network for general purpose data transfer and sub-nanosecond accuracy time transfer. Its initial use was as a timing distribution network for control and data acquisition timing of the accelerator sites at CERN as well as in GSI's Facility for Antiproton and Ion Research (FAIR) project. The hardware designs as well as the source code are publicly available. The name of the project is a reference to the White Rabbit appearing in Lewis Carroll's novel Alice's Adventures in Wonderland.
This glossary defines terms that are used in the document "Defining Video Quality Requirements: A Guide for Public Safety", developed by the Video Quality in Public Safety (VQIPS) Working Group. It contains terminology and explanations of concepts relevant to the video industry. The purpose of the glossary is to inform the reader of commonly used vocabulary terms in the video domain. This glossary was compiled from various industry sources.
Color television as introduced in North America in 1954 is best described as being 'colored' television. The system used the existing black and white signal but with the addition of a component intended only for television receivers designed to show color. By careful application this 'colored' signal was ignored by ordinary TV sets and had negligible effect on the appearance of the black and white image. This meant that color programs were viewable on the many existing black and white receivers which fulfilled a requirement for 'compatibility' desired by the television industry. Once the so-called 'composite' video signal containing the color component had been generated it could be handled just as if it were a black and white signal, eliminating the need to replace much of the existing TV infrastructure. Colorplexer was the RCA name for the equipment that created this 'composite' color signal from three separate images each created in the primary colors, Red, Green and Blue supplied by a color video camera. This process was by the standards of the day quite complex and demanded accurate control of all the various parameters involved if an acceptable color image was to be achieved. The simplification afforded by this 'head end' approach became evident and contributed to the gradual acceptance of color programming over the following decades.
Tri-level sync is an analogue video synchronization pulse primarily used for the locking of high-definition video signals (genlock).
Black and burst, also known as bi-level sync and black burst, is an analogue signal used in broadcasting. It is a composite video signal with a black picture. It is a reference signal used to synchronise video equipment, in order to have them output video signals with the same timing. This allows seamless switching between two video signals.