RS-232—An Electronic Industries Association (EIA) serial digital interface standard specifying the characteristics of the communication path between two devices using either DB-9 or DB-25 connectors.
This standard is used for relatively short-range communications and does not specify balanced control lines. RS-232 is a serial control standard with a set number of conductors, data rate, word length, and type of connector to be used.
The standard specifies component connection standards with regard to the computer interface. It is also called RS-232-C, which is the third version of the RS-232 standard, and is functionally identical to the CCITT V.24 standard.
Raceway—An enclosed channel of metal or nonmetallic materials designed for holding wires, cables, or busbars, with additional functions. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquid-tight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.
Rack Unit—As defined by the Electronics Industries Association (EIA). In reference to product rack height, a unit is a universal measurement: 1.75 inches or 44 mm. 1U (Unit) high refers to 1.75 inches, 2U high refers to 3.5 inches, etc.
Radiation Pattern—The way in which a speaker disperses sound.
Radio Frequency (RF)—Generally refers to signals such as radio and TV broadcast signals, or radio frequency control signals; the range of frequencies used for electrical transmission.
Radio Frequency Interference(RFI)—Tendency of a radio transmission to interfere with other electronic signals. Radio frequency energy is radiated by all electrical equipment - when it is a strong enough signal it becomes interference in audio systems.
RAM—Random Access Memory. RAM is volatile memory that can be written to and read from. RAM is the working memory where active programs and data are stored. RAM normally loses its contents when power is removed. Also see "PROM."
Random Error—Errors in measurement that lead to measured values being inconsistent when repeated measures of a constant attribute or quantity are taken.
Random Noise—Known as “white noise.” A noise signal that never repeats and has a flat frequency spectrum. Random noise can also be a digital pattern that never repeats. Random noise is generally considered to have a Gaussian amplitude distribution, but numerically generated noise can also have a flat amplitude distribution. The amplitude of random noise is normally measured as the rms value.
Rarefaction—The action of the molecules moving apart.
Raster—A raster is the series of scan lines that make up a TV picture or a computer’s display. The term raster line is the same as scan line. All of the scan lines that make up a frame of video form a raster. Lines and rows of dots such as those on the illuminated face of a video screen. A matrix of pixels or the scan lines on a CRT.
Ratio—The comparison of two quantities.
RC Network—An electrical network that is constructed using a resistor and capacitor in parallel, and acts as an effective high-pass filter.
RCA Plug—A connector type most often used with line level audio signals and composite video. (Phono)
Real Images—Are collected from the real world through image sensors. Video collected from film or electronic cameras can be considered real images.
Real-Time—A system is said to be real-time if the operation delivers a correct value in the time and frequency in which it is required. The video system applied in North America, NTSC requires a real-time system capable of delivering 30 frames per second.
Real-Time Analyzer—A device that measures room acoustics in real time, typically using pink noise.
Rear Projection Screen—A translucent screen with a special coating that allows an image to be projected through the screen from the rear, instead of from the front.
Rear Screen Projection—A presentation method in which the image is projected through a translucent screen toward the audience.
Receive–Rx—In fiber optics, to detect an optical signal from a fiber optic cable using a photodetector, such as a PIN diode, APD, or PIN-FET, and convert it to an electrical signal. The receive port of a transceiver.
Receiver—In fiber optics, this is the device at the receiving end of a fiber optic system that converts an optical signal to an electrical signal, and houses the necessary signal processing to output telecommunications, data, or A/V signals.
Receiver Sensitivity—The minimum optical power necessary for the photodetector in a receiver to achieve a specified BER - Bit Error Rate or other performance specification such as signal-to-noise ratio.
Reclocking—Reclocking is a process that is used to restore the amplitude, rise and fall times, and clock rate attributes of a digital signal. Reclocking can add a small amount of time delay to the signal.
Reconstruction Filter—A lowpass filter used to reduce aliasing and to soften the digital edges in an image. Without the reconstruction filter, images may have a Moiré pattern. On Extron products, this feature, referred to as Filter Mode, is selected to be either “ON” or “OFF.” The Filter Mode is intended for use with digital projectors. The feature should, however, be turned off when using CRT displays.
Redundancy—Repeated data or equipment which provides a backup if the primary data or equipment fails.
Re-Equalization—A Home THX technology that reduces the amount of treble on playback so that you hear a more natural-sounding reproduction when a film soundtrack is played back in the home
Reflectance—In fiber optics, the ratio of optical power reflected to the incident power at a connector junction or other component or device. It is expressed as a negative value in decibels – dB.
Reflections—With video signals, reflections can be caused by energy that is not absorbed by the load (or a termination) and is reflected and possibly combined with the original signal. Reflected signals can occur when the impedance does not match (as a result of wrong termination or mixing of cable impedance). Some of the undesirable results of reflection include Y/C delays, color smearing, ringing on luma (but not on color), and ghosts. In fiber optics, abrupt changes in the direction of light at an interface between two dissimilar media so that the light returns to its origin.
Reflective Technology—Any display device that reflects light to create an image.
Refraction—The change in direction of light as it passes from one medium to another, dissimilar medium. Refraction also occurs as light passes through a graded-index medium in which the refractive index varies within the medium.
Refractive Index—Also known as the Index of Refraction, the ratio of the speed of light in a vacuum to the speed of light in a material.
Refresh Rate—Also called “Vertical Scan Frequency” or “Vertical Scan Rate”. The number of times in a second that display hardware draws a new video frame.
Relay—A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.Remote control - A wired or wireless device for controlling the function of another device at a distance.
Remote Socket—A small socket on a VCR or video camera* which permits remote control from any unit which is connected to it. Through the remote socket on a VCR, commands such as Play, Pause and Record can be initiated.
Repeater/Regenerator—A repeater is a device that detects a weak signal and boosts its power for continued transmission. A regenerator receives a signal and regenerates or reconstructs its waveform for transmission.
Resistance—The property of a material to impede the flow of electrical current, expressed in ohms.
Resistor—An electrical component that limits the flow of current via resistance or impedance. It allows a specific amount of current to flow, as determined by the voltage applied to the resistor.
Resolution—The density of lines or dots that make up an image. Resolution determines the detail and quality in the image. A measure of the ability of a camera or video system to reproduce detail, or the amount of detail that can be seen in an image. Resolution is often expressed as a number of pixels, but more correctly, it is the bandwidth. A sharp, clear picture has high resolution.
Resolution (Horizontal)—The amount of detail in a horizontal direction in a video image. It is expressed as the number of distinct vertical lines, alternately black and white, that can be seen in the width of the picture. This information is usually derived from observation of the vertical wedge of the test pattern. Horizontal resolution depends on the high frequency amplitude and phase response of the pick-up equipment, as well as the transmission medium and the monitor itself.
Resolution (Vertical)—The amount of resolvable detail in a vertical direction in a video image. It is expressed as the number of distinct horizontal lines, alternately black and white, that can be seen in a test pattern. Vertical resolution is primarily determined by the number of horizontal scanning lines in a frame.
Resonance—(1) Electronically, the condition where the inductive reactance and capacitive reactance are equal. (2) Acoustically, an intense and prolonged sound produced by a sympathetic vibration.
Retrace—During the scanning of a picture onto a screen, scan lines are produced from left to right. Before scanning the next line, the electron beam must get back to the left side of the screen. This is called retrace. The beam must be turned off (blanked) during retrace time. (See “Horizontal blanking” and “Vertical blanking.”) A retrace problem could appear as missing video information on the left side of the screen.
Retrace Time—Time required to move the scanning beam from the right side to the left side of the screen.
Retro—A rear-projection video display.
Retro Unit—Self-contained rear projection system.
Return Loss—A measure of reflected energy in decibels at a specific frequency and cable length.
Reverberant Sound—Sound waves that bounce off of multiple surfaces before reaching the listener, but arrive at the listener's ears quite a bit later than early reflected sound.
Reverberation—The persistence of sound in an enclosed space, as a result of multiple reflections after the sound source has stopped. The decaying residual signal that remains after a sound occurs, created by multiple reflections as the original sound wave bounces off walls, furniture, and other non-absorbing barriers within a room or other acoustical environment. A room with very little reverberation is called a “dead” room, which is the opposite of a “live” acoustic space which is very reflective.
Reverberation Time—The length of time required for the sound field to collapse, after the sound source has stopped.
RF—Radio frequency. A range of frequencies used for electromagnetic transmission (e.g., radio and TV).
RF Adapter—A device that allows video and audio signals from a video tape recorder (VTR) or computer to be shown on a standard TV receiver. This device produces comparatively poor resolution and picture quality. Also called “RF converter.”
RF Control—A medium of remote control from which signals are sent to the controlled equipment via data pulses modulated on an RF carrier signal.
RF Conversion—A process which takes low frequency signals such as audio and video and, via an RF modulator, converts them to higher (broadcast) frequencies suitable for radio or TV reception.
RF Distribution—The process of supplying an RF* signal to several acceptors simultaneously. During RF distribution, RF amplification* and proper input and output matching should be performed in order to avoid signal losses.
RFI—Radio Frequency Interference. High frequency interference from transmissions such as telephones, microwaves, and television stations.
RF System—A closed circuit system becomes an RF system when the composite video and audio signals are modulated at a certain frequency, called a channel. RF systems require a display device (e.g. TV) with a tuner set to a selected channel to display the information modulated onto that frequency.RG/U—Radio Guide/Universal. Military abbreviation for coaxial cable.
RGB—Red, Green, and Blue. The chroma information in a video signal. The basic components of the color television system. They are also the primary colors of light in the additive color process.
RGBHV—Red, Green, Blue, Horizontal, and Vertical Sync. A five-wire signal where the red, green, and blue video signals, as well as the horizontal and vertical sync signals, are on its own conductor.
RGBS—The Red, Green, and Blue chroma information in a video signal, with a separate channel for the sync signal.
RGsB—Red, Green, Blue, and Sync on Green. A three-wire signal with separate red, green, and blue video signals with the sync (horizontal and vertical) on the green signal.
Ribbon Cable—A cable with several copper wires or optical fibers, each jacketed side-by-side in a flat, ribbon-like structure.
Ribbon Splice—The splicing of individual optical fibers of a ribbon cable, with each fiber spliced on a groove of a substrate or etched silicon chip. Each groove is spaced evenly and a flat cover holds the fibers in place on the substrate.
Ring—A network topology that connects terminals, computers or nodes in a continuous loop.
Ripcord—A cord of strong yarn, situated under the cable jacketing, used to facilitate in stripping and removal of the jacket.
Ripple—Generally referring to the wavelike variations in the amplitude response of a filter.
Rise Time—The time required for a signal to go from 10% to 90% of its maximum amplitude level.
Riser—A type of cable designed for vertical runs in shafts spanning multiple floors in a building.
RJ—Registered Jack. A type of modular jack that is similar to those used with telephones. Examples: RJ-11 = 4 or 6 wire module, RJ-45 = 8-wire module.
RJ-45—Registered Jack-45. A connector similar to a telephone connector that holds up to eight wires, used for connecting Ethernet devices.
RMS—An acronym for “root mean square.” Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.
ROM—Read Only Memory. Permanent memory that can only be loaded once, normally by the manufacturer. Contents may not be altered or removed.
Room Mode—An acoustical resonance in a room caused by parallel wall surfaces. Any set of parallel walls will establish a series of standing waves, the lowest one of which has the wall spacing as a half-wavelength. These sound waves interfere with one another to produce a series of places where the SPL is high and another series of places between then where the SPL is very low. It is as if the sound wave were stationary between the two surfaces.
Rooming—With large matrix switching systems, such as the Extron Matrix 3200/6400 Series Switchers, specific outputs can be assigned to a room. That room sees only those outputs, even though they are part of a total switching system. The outputs seen by a room have virtual numbers (may be different from the physical numbers). Room presets using those outputs can be saved and recalled without affecting other switcher outputs.
Router—A network device that forwards packets from one network to another. Routing is a layer 3 function. Routers forward packets based on programmed or “learned” routing tables. Each incoming network packet is examined and a decision is made where to forward it. The destination address in the packets determines which port outgoing packets are directed to. In large-scale enterprise routers, the current traffic load, congestion, line costs and other factors determine which line to forward to.
RS-170A—EIA technical standard for NTSC color TV. A video standard that ensures proper synchronization of video signals and components.
RS-330—An EIA technical standard that provides details for industrial closed-circuit television (CCTV).
RS-343A—An EIA standard for high resolution monochrome CCTV.
RS-422—An EIA serial digital interface standard that specifies the electrical characteristics of balanced (differential) voltage, digital interface circuits. This standard is usable over longer distances than RS-232. This signal governs the asynchronous transmission of computer data at speeds of up to 920,000 bits per second.
RS-485—An EIA standard for multipoint communications. It is similar to RS-422, but can support several nodes per line because it uses lower impedance drivers and receivers and allows for addressing.
RsGsBs—Red, green, and blue signals with composite sync added to each color channel; referred to as "RGB sync on all three”. It requires three cables to carry the entire signal.
RTP—Real-time Transport Protocol, an IETF standard for streaming realtime multimedia over IP in packets.
RTSP—Real Time Streaming Protocol. A network control protocol designed for use in entertainment and communications systems to control streaming media servers.
Run Length Encoding—Simple form of data compression in which runs of data are stored as a single data value and count, rather than as the original run. This is most useful on data that contains many such runs: for example, relatively simple graphic images such as icons, line drawings, and animations.