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Dictionary of Technical Terms - P
path length (propagation delay)
The time it takes for a signal to travel through a piece of equipment or a length of cable. In digital picture manipulators, the values of the field rate information produced by in-betweening two key frames. Visually, the path corresponds to the motion route that the image on the screen takes to move from one key frame to the next. May also include size changes, picture rotation, etc. In a production switcher, a variety of geometric shapes called patterns are available that can be used for wipe transitions, key masks, etc. A variable-width border that occurs at the edges of a wipe pattern. Typically, the border can be filled with matte video from a border matte generator. In production switchers, the group of controls used for selecting and modifying wipe patterns. See preset pattern. In video switchers, a special wipe edge modulation effect produced by summing a matrix pattern and an analog pattern together. An oscillation or modulation of the vertical and/or horizontal dimensions of a wipe pattern edge. In video switchers, moving a wipe pattern using a joystick. In a production switcher, the pushbuttons used to select wipe patterns. See Y, Pr, Pb. Private branch exchange. An insulating board onto which a circuit has been printed or etched. Personal communications network. Personal communications service. The point of highest amplitude of a waveform or voltage. The amplitude (voltage) difference between the most positive and the most negative excursions (peaks) of an electrical signal.
phase (chroma phase, hue, tint)
The relative timing of a signal in relation to another signal. If the time for one cycle of a signal is represented as 360 degrees along a time axis, the phase position for the second signal is called phase angle expressed in degrees. The subcarrier phase of TV colors can be adjusted and this changes the hue of the colors themselves. A picture defect caused by unequal delay (phase shifting) of different frequency components within the signal as they pass through different impedance elements—filters, amplifiers, ionospheric variations, etc. The defect in the picture is ``fringing'' (like diffraction rings) at the edges where the contrast changes abruptly. A picture defect caused by the incorrect relative timing of a signal in relation to another signal. The condition whereby the output of a circuit produces a wave of the same shape and frequency but 180 degrees out of phase with the input.
pre-equalization (pre-emphasis)
To emphasize certain frequencies in a signal, usually before transmission, in order to improve the signal-to-noise ratio or to reduce distortion of the signal. The condition of an injection laser corresponding to the emission of predominantly incoherent or spontaneous radiation. In telecommunications, a pre-stored list of connect commands that can be implemented by a single MML statement. A regulator used to deliver reduced voltage to all amplifier modules to ensure cooler operation. A specific amount of time allowed for tape machines to run prior to an edit in order to get them up to speed and synchronized for the edit. In preparation for the edit, tapes are cued to a point ahead of the edit point to provide a proper preroll. The amount of preroll required varies with each type of VTR. In video switchers, to make a crosspoint selection prior to performing a transition that will take the selection to air. Another term for "master control switcher" used in Europe and some other countries outside the U.S. There are minor differences applicable to the specific area of use. 1. To select a video source in preparation for taking it to air. 2. A source selected on the preset bus or the action of selecting a source on the preset bus. In video and audio switchers, a row of crosspoint pushbuttons used to select the video or audio input that will be placed on-air during the next background transition. Also called preset background bus. A transition mode in which one video signal is faded to color black before the other video signal is faded up. An effect in which a wipe pattern that has been preset to a size limit by the user becomes the key source (cuts the key hole). The characteristics of the pattern are set using the pattern controls. See preset pattern. A series of affordable, high quality character generators made by Grass Valley. 1. To rehearse an edit without recording it. 2. To look at a video effect before taking it to air. The crosspoint bus used for selecting the signal that will appear at the preview output of a switcher. The output of the switcher that allows you to observe an effect before it is placed on-air. Primary rate interface. A small group of colors that, when combined, can produce a broad spectrum of other colors. In television, red, green, and blue are the primary colors from which all other colors in the picture are derived. The main video inputs applied to the crosspoint buses of a switcher. In video mixers and manipulators, the position of a layer of video relative to other layers. Layer A is said to have priority over Layer B when Layer A is placed on top of Layer B. See also layering.processing amplifier (proc amp)
A device that stabilizes the composite video signal, regenerates the synchronizing pulses and color burst, and can make other adjustments to the video signal. In desktop editing, the building blocks of a video production, including clips, effects, transitions, and graphics. Also known as post production house. A facility that typically does everything to generate final video productions except shooting of original videotape. Services typically include editing raw master tapes, modifying, creating new effects, and correcting. Projects typically include advertising, training, promotion, music videos, and television shows and movies. A device that allows transitions between different video pictures. It may also contain a special effects generator. A video production market segment that includes educational, corporate, military, and small commercial producers of video programs. 1. The on-air crosspoint bus of a video or audio switcher. 2. The on-air output signal of video or audio equipment. 3. A sequence of instructions used to tell a computer how to receive, process, store, and transfer information. In video and audio switchers, a row of crosspoint pushbuttons used to select the on-air video or audio background output of the switcher or mix/effects. Also called program background bus. A video monitor dedicated to displaying the program output of a device or studio. The on-air or final output of a switcher or other device, or a studio. A video mixing system that combines two crosspoint buses with a video mixer. On live production switchers, a program/preset mixer is usually included following the mix/effects and includes pushbuttons for selecting the output of each mix/effect. See background video.programmable general purpose interface (GPI)
An interconnection scheme (usually serial) that allows remote control of certain selectable functions of a device by some other device that can be programmed to select the desired functions. A trademarked GVG editor feature that allows control of VTR speed during editing. Programmable Read Only Memory. A ROM that can be programmed by the equipment manufacturer (rather than the PROM manufacturer). A cue to help the operator choose the next action. A Grass Valley system for playing network promos while keying effects, animations, and affiliate ID logos into the network signal under control of either the network or affiliate.propagation delay (path length)
The time it takes for a signal to travel through a circuit, piece of equipment, or a length of cable. A control panel function that locks a source-to-destination configuration so that other control panels may not change that configuration. A set of conventions governing the format and timing of message exchanges to control data movements and correct errors. Power supply. Public Service Commission. Preset. Preset pattern. Public Utilities Commission A change in voltage that has identifiable beginning and ending points. A momentary deviation from and return to a constant voltage level. A method of editing in which the system counts control track pulses to find locations on the tape.pulse delay distribution amplifier
A device used to replicate an input timing signal, typically providing 6 outputs, each of which is identical to the input signal but shifted in time by as little as a few nanoseconds to as much as a microsecond or more. A device used to replicate an input timing signal, typically providing 6 outputs, each of which is identical to the input signal. May also perform cable equalization or pulse regeneration. A set of signals needed by some source equipment for timing purposes. The signal set may be composed of any of the following: sync, blanking, subcarrier, horizontal drive, vertical drive, burst flag, and burst gate/PAL pulse. The leading or trailing edge of a pulse is defined as the 50% point of the pulse rise or fall. The interval of time required for the edge of a pulse to fall from 90% to 10% of its peak amplitude. The voltage amplitude of a pulse. Device which accepts reference color black or another composite color video input and processes it to produce sync, blanking, subcarrier, and burst flag (PAL only) reference pulses. The interval of time required for the leading edge of a pulse to rise from 10% to 90% of its peak amplitude. The widening of the input optical signals as they traverse the length of a fiber. Caused by the fact that different frequencies of light traverse the path at different velocities. This property limits the useful bandwidth of the fiber. Usually expressed in nanoseconds per kilometer. A K-factor (distortion) measurement using a T pulse and bar video test signal. See also T-pulse to bar. The interval measured between the 50% amplitude points of the leading and trailing edges. Private virtual network. Preview.We've recently redesigned our website so your bookmarked links may no longer work. Please use either the search bar at the top right of this page or select an area from one of the tabs above to find what you are looking for.
