Path—A path, the general form of the name of a file or directory, specifies a unique location in a file system. A path points to a file system location by following the directory tree hierarchy expressed in a string of characters in which path components, separated by a delimiting character, represent each directory.
Packet—A block of data that is transmitted over a network in a packetswitched system. A packet is also referred to as a frame or datagram.
Packet Jitter—The term jitter is used as a measure of the variability over time of the packet latency across a network. In real-time applications such as VoIP and video, variation in the rate at which packets in a stream are received that can cause quality degradation. Video decoders must account for jitter which may be experienced delivering packets across a network.
Packet Loss—Occurs when one or more packets of data traveling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications; the other two being bit error and spurious packets caused due to noise. Packet loss is typically experienced in the real world as a random burst of packet loss.
PAL-Phase Alternate Line—A television standard in which the phase of the color carrier is alternated from line to line. It takes four full pictures (8 fields) for the color-to-horizontal phase relationship to return to the reference point. This alternation helps cancel out phase errors. For this reason, the hue control is not needed on a PAL TV set. PAL, in many transmission forms, is widely used in Western Europe, Australia, Africa, the Middle East, and Micronesia. PAL uses 625-line, 50-field (25 fps) composite color transmission system.
Palplus—A widescreen TV standard (16:9 format) used mainly in Europe for creating a "better-looking" image on the screen. It employs special technology for color and luminance image enhancement and resembles the HDTV format. It shows as a letterbox on a regular TV.
Pan and Scan—A method of converting a widescreen presentation to an image within a 4:3 aspect ratio without black bars at the top and bottom of the picture. The camera moves back and forth (panning and scanning) in each scene to show only the most important parts of the image. Results in the left and/or right edges of the image being cut off.
Panelboard—A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices. A panelboard may be equipped with switches for the control of light, heat, or power circuits. It is designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support, and accessible only from the front.
PanelLink®—Silicon Image’s TMDS (Transition Minimized Differential Signaling) all-digital video transmission standard. PanelLink technology was designed to provide the bandwidth necessary to support digital displays.
Panning—The side-to-side movement of sounds and images from one location to another. Originally a camera term.
Parametric Equalizer—A type of audio equalizer having several “parameters” for control of various filters that can be applied to audio signals. Parametric equalizers are most widely used in situations where very fine control over the audio signal is desired, and provide control over gain, Q (Quality factor, a measure of a resonant system), and frequency. (See EQ-Audio)
Passive Crossover—A crossover network that divides audio frequencies without any active amplification or buffering components and which uses only resistors, capacitors and inductors.
Passive Optical Network-PON—A fiber optic network comprising singlemode fiber, passive splitters, and passive couplers for a service provider to deliver fiber to the home – FTTH, or fiber to the building – FTTB.
Passive Subwoofer—A speaker for reproducing bass frequencies that must be powered by a separate power amplifier. Contrasted with “active” or “powered” subwoofers, which contain built-in amplifiers.
Patch Cord—A predetermined length of cable with connectors at both ends, also known as a cable assembly, patch cable, or jumper.
Patch Panel—A passive device, typically flat plate holding feed-through connectors, that allows temporary circuit arrangements and rearrangements by simply plugging and unplugging patch cables. In fiber optics, this is also known as a cross-connect panel, and is used for interconnection of multiple cables or fibers.
PC—Personal Computer or Projector Control.
PCB—Printed Circuit Board.
PCM-Pulse Code Modulation—The digital representation of an analog audio signal. PCM is the standard form of digital audio in computers and the compact disc (CD) “red book” format, as well as the standard used for the audio portion of digital video recording.
PCX—A graphics file format developed by Zsoft Corp. This format, which is raster based, supports graphics from monochrome up to 24-bit color (16 million colors).
PDF-Portable Document Format—A type of format developed by Adobe Systems with which the same file can be opened and viewed on most any computer platform (PC, Mac, Unix). It can also be printed on most any printer (dot matrix, laser, inkjet, PostScript, or non-PostScript). A PDF is a document file in that it includes text and graphics in one file that maintains the appearance of the original.
Peak—The highest level of signal strength, as determined by the height of the signal’s waveform.
Peak White—The whitest portion of a picture signal.
Peaking—A means of compensating for mid- and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. The higher the frequency and longer the cable length, the more peaking may be required.
Peaking Control—Peaking control on Extron products compensates for mid- and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. When using the peaking control a noticeably sharper picture will be seen on all displays regardless of cable lengths. However, 100% peaking may provide over enhancement on short cable runs. Use the position that produces the sharpest image on the display screen. Also called “sharpness” control.
Peak-to-Peak—Abbreviated “p-p.” The difference in amplitude (voltage, for example) between the most positive and the most negative excursions (peaks) of a signal.
Pedestal—A small DC step (sometimes called setup), within the video signal separating active video* from the blanking level, which indicates the picture’s black-level*. It is used as a reference in a standard video signal for the white level and all the gray levels in between. Only NTSC uses a pedestal - usually a 7.5 IRE step.
Perceptual Coding—A method of reducing the number of bits needed to encode an audio or video signal by ignoring information unlikely to be heard or seen. Also called “lossy compression.”
Peripheral Device—Normally an external device that a CPU communicates with, such as a printer, mouse, disk drive, or interface.
Persistence—In video, persistence is the staying power of a lighted phosphor, since a phosphor begins to dim after being excited by the electron beam. A long-persistence phosphor allows the screen to dim more slowly. Long-persistence phosphors are commonly used for CRT projection in 3D applications.
P-Frame—Predictive coded picture. Contains predictive information required to recreate a video frame.
Phantom Center-Channel Mode—A setting on A/V receivers or A/V controllers invoked when no center-channel speaker is used.
Phantom Image—The creation of an apparent sound source between two speakers.
Phantom Power—A standardized method of providing power to condenser microphones using the two signal leads of a balanced audio connection. An international standard, IEC 60268-15, defines three DC voltages, 48 V, 24 V, and 12 V. In professional applications, 48 V Phantom power is the most common.
Phase—The relative timing of one signal to another, usually expressed in degrees of shift.
Phase Error—A change in the color subcarrier* signal whereby its timing is moved out of phase, i.e., occurring at a different instant relative to the original signal. Since color information is encoded in a video signal as a ratio between the modulated color signal and the color burst* phase, a deviation in the color subcarrier phase results in a change in the hue* of the picture. In NTSC* video transmission, phase error results in a substantial change in the hue. In PAL, small changes in hue are automatically corrected, and only a minor reduction in color saturation* occurs. The hue remains consistent.
Phasing Adjustment—To properly synchronize an NTSC/PAL video output signal to a genlock signal, a phasing adjustment to the horizontal phase and the subcarrier phase may be required. The horizontal phase difference between these two signals must be set to zero. Likewise, the subcarrier phase difference between these two signals must also be set to zero.
Phoenix®—A molded, plastic, captive screw connector whose termination requires that you strip and slide a wire directly into a hole on the connector (compression termination).
Phone Connector—An audio connector used as a loudspeaker connector. Common types are 1/4 inch and 1/8 inch.
Phone Plug—A small, round audio plug used as a speaker connector. Also called 1/4” phone plug.
Phono—The European name for an RCA connector.
Phono Plug—A plug most often used with line level audio signals. Also known as an RCA plug.
Phosphor—The chemical coating on the inside of the CRT screen that emits light (monochrome or color) when struck by an electron beam. Each dot on the screen is actually a phosphor that glows for a period of time. Also see "Persistence."
Photodetector—A device that senses incoming light and outputs an electrical signal in response to the light.
Photon—A elementary unit of light with both waveform and particle properties.
Physical Contact-PC—In fiber optics, the point at which a glass surface, such as that of a fiber, physically touches another glass surface, usually that of a connector. PC polished connectors can be used with SPC or UPC polished connectors but are not compatible with APC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment. Multimode applications always use PC, SPC, or UPC polished connectors.
Physical Plant—Infrastructure components including cable, connectors, splices, panels, splitters, repeaters and regenerators necessary to propagate the light signal between the transmitters and receivers of a fiber optic system.
Pict/pct/pic—The most popular Macintosh graphics file format, bitmap based, supporting from monochrome up to 24-bit color images.
Picture Border Softness—A border created while one video image is inserted into a designated area in another (in a circle, rectangle or almost any other shape) by using a special effects generator* or another keyer. This border* between the two images can vary from a sharp line to a vague blending of images between the two pictures. One of the features in special effects generators is picture border (edge) control. It allows the user to control both the color and the sharpness or fuzziness (softness) of the border between the two images.
Picture Element/Pixel—The smallest "dot" on the TV or monitor screen usually comprised of tri-color dots: red, green and blue. The PIXEL size is a measure of the screens' maximal apparent resolution.
Picture Sharpness—The quantity of fine details in a video picture. A picture appears sharp when it contains fine details, extended micro-contrast (the distinction between fine details and the surrounding background) and sharp, thin edges. Picture sharpness is easily lost during the recording process and, to a lesser extent, during playback*. Advanced video enhancement equipment is used to improve picture sharpness, especially micro-contrast. Potential losses, which might damage an image during video processing, are automatically pre-compensated. Although picture sharpness is a subjective factor, it is technically measurable as the ratio between high frequency signals (about 2 MHz) and low frequency signals. In the digital domain, the apparent picture sharpness corresponds exactly to that of the source signal, and if affected, it is usually due to the monitor's ability to resolve picture details.
Pigtail—A short length of cable with one end terminated with a connector and the other end spliced or hard-wired to existing cable or equipment.
Pigtail Assembly—A short length of fiber optic cable with one end terminated with a connector, and the other end fixed to a transmitter, receiver, or long length of cable via a splice.
Pin Cushion—The inward or outward (curved) appearance of the edges of a display.
PIN Diode-Positive Intrinsic Diode—A type of photodiode, or optical signal transducer that converts light to an electrical signal, used in fiber optic receivers.
Pin Out—An illustration or table that names signals, voltages, etc., that are on each pin of a connector or cable.
PIN-FET—Positive Intrinsic Negative Field Effect Transistor.
Ping—The Packet INternet Groper (ping) command is used to test connectivity between IP devices. The Internet Control Message Protocol (ICMP) echoes Ethernet packets to determine whether a network device is active and what the bidirectional delay is in communicating with it.
Pink Noise—A type of random noise that contains an equal amount of energy per octave. The bands 100-200, 800-1600, and 3000-6000 all contain the same amount of energy. Since pink noise is based on octaves rather than individual frequencies, there is no increase in energy in the high octaves. Because of this, and because Real Time Analyzers (RTA) tend to look at octave or 1/3 octave ranges, pink noise is very useful for measuring the frequency response of audio equipment, as well as for determining room response for sound reinforcement applications.
PIP-Picture-in-Picture—A small picture within a larger picture created by scaling down one of the images to make it smaller. Each picture requires a separate video source such as a camera, VCR, or computer. Other forms of PIP displays include Picture-by-Picture (PBP) and Picture-with-Picture (PWP), which are commonly used with 16:9 aspect display devices. PBP and PWP image formats require a separate scaler for each video window.
Pitting—In fiber optics, an undesirable endface polishing condition resulting from the use of lapping film that has been contaminated with fiber optic and grit particles. Pitting can also denote small cracks in the endface due to exposure of cleaning agents to intense light through a fiber.
Pixel-Picture Element—The smallest unit or area of a video screen image that can be turned on or off, or varied in intensity.
Pixel Clock—Dot clock. The pixel clock divides the incoming horizontal line of video into pixels. This pixel clock has to be stable (a very small amount of jitter) relative to the incoming video or the picture will not be stored correctly. The higher the frequency of the pixel clock, the more pixels that will appear across the screen (pixel resolution).
Pixel Loss—A video problem in which picture information is missing, giving the appearance of specks in the image.
Pixel Phase—An adjustment common to scalers and projectors, which adjusts the point in time that a sample is taken in the A-D conversion process. The pixel (or dot) clock in a computer and the pixel clock in a display device may operate at the same frequency for a given resolution and refresh rate, but not necessarily in phase with each other. Pixel phase adjustments are provided on digital monitors and projectors to synchronize the two independent clocks. A test generator like the Extron VTG 300 includes an alternating pixel pattern, which is used to eliminate banding and shimmering artifacts that are symptomatic of pixel phase error.
Pixel Resolution—In computer graphics and video images, the number of pixels in the display. For example, a picture with 1,024 x 768 pixels is much sharper, or has higher resolution, than a picture with 640x480 pixels. The total number of pixels is the product of these two numbers.
Plane—In matrix switchers, a plane refers to all of the inputs and outputs of one signal. For example, the red plane would include all of the inputs and outputs for red signals; the blue plane would include all of the blue signals.
Plane Breakaway—On matrix switchers, the ability to break one of the planes away from the others. Generally the video, sync, and audio planes will switch the same way (i.e., have the same switching pattern). With plane breakaway, an individual plane can be set up to switch independently of the others.
Plane Grouping or I/O Grouping—When a number of independent planes on a matrix switcher are all grouped so they switch in unison.
Plasma Display Panel (PDP)—Fixed-pixel video display device in which an electrical charge ionizes gas inside a glass-matrix array, causing phosphors on the glass to emit light. Current plasma panels range in size from 42 to 71 inches, and are about three inches thick.
Plastic Optical Fibers—Optical fibers in which the core and cladding are made of plastic. The diameter of the core is often larger than that of glass fiber.
Playback—The process whereby a videotape on some other video source (DVD*, etc.) is displayed on the monitor. During playback, analog or digital video enhancement, carried out on a video processor, can be incorporated into the signal to alter, correct or restore it.
Plenum Cable—Cable having a covering (jacket) that meets UL specifications for resistance to fire.
Plug—In A/V and fiber optics, this is also known as the male connector.
PLUGE-Picture Line Up Generation Equipment—This is the name of a test pattern that assists in properly setting picture black level. PLUGE can be part of many test patterns. The phrase and origination of the test signal are both credited to the British Broadcasting Company.
Plug-in—A program of data that enhances, or adds to, the operation of a parent program. Software decoders often use a plug-in provided in media players.
Point-Source—A sound system that has a central location for the loudspeaker(s), mounted high above, intended to cover a large area; typical of a performance venue or a large house of worship.
Point-to-Point—A videoconference between two locations, like a telephone call.
Polarity—The positive and negative orientation of a signal. Polarity usually refers to the direction or a level with respect to a reference (e.g. positive sync polarity means that sync occurs when the signal is going in the positive direction).
Polar Pattern—(or pickup pattern); the shape of the area that a microphone will be most sensitive to sound.
Polishing Paper—A plastic polishing sheet for optical fiber or connector endfaces with fine grit on one side.
Polishing Puck—A fixture for optical fiber endface polishing, used to support a fiber optic connector ferrule in place, properly aligned to the lapping film.
Polyethylene—One of the Polyolefins used for Insulation of Non Plenum Wires and also in the Foaming form as Dielectric for all Non Plenum COAX.
Polyolefin—Family of Compounds consisting of Polyethylene , Polypropylene , PolyButylene etc.
Porch Front/Back—A short period of time, of several microseconds, before and after the sync pulse that is a part of the blanking period, riding on blanking signal level. The porch can be used for clamping purposes, as it does not carry visible picture information.
Port—A connection for an input or output device. Typical ports found on a computer include serial, parallel, SCSI, disk drive, video, and keyboard ports.
Port Number—A preassigned address within a server that provides a direct route from the application to the Transport layer or from the Transport layer to the application of a TCP/IP system.
Posterization—The conversion of a standard video image into a picture which consists of a few large single-colored areas. Graduations of fine color and brightness are totally removed. The result is a crude, harsh image. This is a typical special effect* available on special effects generators*.
Post Production—All the editing work done with crude video material in the studio after filming. Editing, special effects insertion, image enhancement, and other processes enriching and fine-tuning the production are done in a studio during post-production.
Potentiometer—A variable resistor. Potentiometers typically have three terminals: the two end terminals, across which the entire resistance appears, and a third terminal, the “wiper”, which moves to a different spot on the resistor as the shaft is turned. In this manner, the resistance between the wiper and one end terminal gets smaller while, at the same time, the resistance between the wiper and the other end gets larger. This allows the potentiometer to be used as a variable voltage divider, for use in attenuators such as volume controls or tone controls.
POTS (Potentiometer)—A potentiometer is a type of resistor featuring variable and adjustable resistance controlled via a sliding or rotating contact. In order to regulate resistance, the potentiometer acts as a voltage divider, lowering or increasing the voltage output by controlling the resistance value. It is usually used to control electronic devices such as the knob that controls volume and other functions in an audio/video equipment.
Power (Electrical)—The dissipation of heat by passing a current through a resistance. Measured in watts [W], Power [P] is expressed by ohm’s law from the three variables: voltage [E] current [I] and resistance [R]. That is, P = I2 x R, or, P = E2/R or P = E x I.
Power Amplifier—An audio component that boosts a line-level signal to a powerful signal that can drive loudspeakers.
Power Conditioners—Power conditioners enhance the quality of power going to equipment by regulating voltage, eliminating noise or correcting other issues.
Power Distribution Unit—A rack-mountable or portable electrical enclosure that is connected by a cord or cable to a branch circuit for distribution of power to multiple electronic devices. A PDU may contain switches, overcurrent protection, control connections, and receptacles.
Power Meter—A device that measures the loss of optical power in a fiber optic connector, fiber optic cable, or fiber optic system.
Power Output—A measure of a power amplifier’s ability, in watts, to deliver electrical voltage and current to a speaker.
Power Supply—Circuitry found in every audio and video component that converts 60Hz alternating current from the wall outlet into direct current that supplies the device’s circuitry.
Power Transformer—Device in a power supply that reduces the incoming voltage from 120V to a lower value.
Powered Ethernet—A standard (IEEE 802.3af) that provides power to network devices by utilizing the existing Ethernet connection, thereby eliminating the need for additional, external power supplies.
Power Handling—A measure of how much amplifier power, in watts, a speaker can take before it is damaged.
Pr/Pb—A color difference signal representing a scaling formula for B-Y and R-Y signals. By using the appropriate formula, 700mVpp of Pr and Pb represent a 100% saturation level in component video.
Preamp-Preamplifier—An electronic circuit that raises a weak signal high enough to be fed into an amplifier.
Pre Enhancement—In many cases, through acquaintance with video equipment, tapes and cables, a user anticipates video losses. Therefore, he can introduce video enhancement into the video signal in advance to compensate and restore the original unattenuated and undistorted signal (See also Line Compensation*).
Presentation Device—A general term used to define a video projector, plasma display, presentation monitor, or other large format data display device.
Preview Bus—A standard function on video special effects generators* which allows the operator to select any of the video sources attached to the device and preview all special effects before he begins video processing. The preview bus is operated through a series of switches on the special effects generator, each of which is assigned to a specific input. Each input signal can be previewed on its own monitor by pressing the relevant switch. This is a rapid and effective method to check work before going on the air.
Primary Colors—Any set of colors from which other colors can be derived. In video, the primary colors are red, green, and blue. Equal amounts of red, green, and blue make white; the absence of all colors makes black.
Primary Optic—The lens that focuses the image onto the screen.
Private Network—A communication network owned by one or more firms for their exclusive use.
Prism—A prism beam splitter filters the light into its red, green, and blue components.
Processing Amplifier—An electronic device that stabilizes, changes, or rebuilds signals.
Profile Alignment System-PAS—A technique for fusion splicing that employs a CCD camera for precisely aligning the cores of two optical fibers.
Program Bus—Similar to the preview bus*. It is also operated through a series of switches, each of which is assigned to a specific input device (special effects generator*, routing switcher*, etc.) One or more input signals can be chosen to be mixed or simultaneously processed in another fashion. The processed output of the program bus is the final product, which goes on the air or to the final edit cut.
Progressive—A method for displaying, storing or transmitting moving images in which all the lines of each frame are drawn in sequence.
Progressive Scan—A method by which all the video scan lines are presented on the screen in one pass instead of two. Typically denoted by the letter “p”, as in “480p”, which indicates a signal with 480 active lines running at 60 frames per second. Also see "Non-interlaced."
Projection—The process of presenting visual media by light transmitted through an optics system to a viewing screen.
PROM-Programmable Read Only Memory—An electronic memory that does not lose its contents when power is removed, and that can be reprogrammed using a special PROM programmer (“burner”). Also see "EEPROM" and "EPROM."
Pro-MPEG Forum—An association of broadcasters, program makers, equipment manufacturers, and component suppliers with interests in realizing the interoperability of professional television equipment, according to the implementation requirements of broadcasters and other end-users. The Forum has been in existence for approximately eight years and has over 130 members.
Propagation Delay—The amount of time that passes between when a signal is transmitted and when it is received at the opposite end of a processor, amplifier, or cable.
Protocol—A set of agreed-upon standards that define the format, order, timing, handshaking, and error checking method for data transfer between two pieces of equipment.
Pseudorandom Noise—A noise that satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a sequence of pulses that will usually repeat itself, albeit after a long time or a long sequence of pulses.
Public Network—A network established and operated by a telecommunications provider, for specific purpose of providing data transmission services for the public. The Internet is a public network.
Pulling Tension—Maximum amount of tension that can be applied to a cable or conductor before it is damaged.
Pulse Broadening—An increase in the duration of a pulse.
Pulse Code Modulation—A method used to convert an analog signal into noise-free digital data that can be stored and manipulated by computer. PCM takes an 8-bit sample of a 4kHz bandwidth 8000 times a second, which gives 16K of data per second.
Pulse Spreading—The dispersion of an optical signal as it traverses along an optical fiber. Also known as Pulse Dispersion.
Pulse Width—The time during which a source, such as a laser, is in an “on” state.
Pulse Width Modulation—A powerful technique for controlling analog circuits with a processor’s digital outputs. PWM is employed in a wide variety of applications, including high power switching amplifiers. By controlling analog circuits digitally, system costs and power consumption can be drastically reduced.
PURE3 Codec—A codec which is capable of encoding and streaming both video and computer graphic inputs and a wide variety of resolutions, preserving equal quality for both signal formats. It preserves a balance between three performance factors low latency, low bandwidth and high image quality. The PURE3 Codec has been optimized for use on IP networks which are acknowledged to be lossy. The codec includes an error concealment system which is highly resistant to network errors without using forward error correction.
PVC-Poly Vinyl Chloride—Used for Insulation of Wires and Jacketing of most Non Plenum Cables.