GLOSSARY

1/3 octave equalizer    A graphic equalizer that provides 30 or 31 slider adjustments corresponding to specific fixed frequencies with fixed bandwidths, with the frequencies centered at every one-third of an octave. The numerous adjustment points shape the overall frequency response of the system. This makes the sound system sound more natural.

4K ecosystem    Video cameras, media players, servers, displays, distribution, and networking technologies used for recording and delivering video at 3840×2160- or 4096×2160-pixel resolution.

8K    A video resolution format. It offers a 7680×4320-pixel resolution, which is 16 times the resolution of full HD.

9-pin connector    The most common type of RS-232 connection that is used within a control system.

acceptable viewing area    The viewing range for a screen suggested as a 45-degree line extending outward from the left-side edge and right-side edge of a displayed image.

access point    A network device that handles a wireless network connection.

acoustic echo canceller    Used in a conferencing system. The canceller will attempt to compensate for environmental echoes that are created by the far-site sound bouncing around the walls and furniture and returned to the microphones.

acoustics    Explains and quantifies the interaction of cyclical mechanical compression and rarefaction of a medium, typically air, occurring within a commonly accepted frequency range of 20 Hz to 20 KHz (the audible spectrum) and the physical environment in which those waves occur.

acuity    An eye’s ability to discern fine details. There are several different kinds of acuity, including resolution acuity, which is the ability to detect that there are two stimuli, rather than one, in a visual field, and recognition acuity, which is the ability to identify correctly a visual target, such as differentiating between a G and a C.

AES    Audio Engineering Society.

allied trade    A business that collaborates with AV professionals to complete a project.

alternating current (AC)    An electric current that reverses its direction periodically.

ambient light    Lighting throughout an area that produces general illumination.

ambient noise    Sound that is extraneous to the intended, desired, or intentional background noise.

amplifier    An electronic device for increasing the strength of electrical signals.

amplitude    The strength of an electronic signal as measured by the height of its waveform.

amperage    The amount of electric current flow within a circuit. Amperage is measurement in amps and expressed using the symbols I or A.

analog    A method of transmitting information by a continuous but varying signal.

analog-to-digital/digital-to-analog (AD/DA) converters    Used to convert signals from analog to digital or from digital to analog.

angularly reflective screen    A screen that reflects light back to the viewer at a complementary angle.

ANSI    American National Standards Institute.

aperture    An opening in a lens regulating the amount of light passing through the lens to the imager.

arrayed loudspeaker system    A loudspeaker arrangement that delivers sound from a single point in space. It is also known as a high-pressure system.

artifact    A small disturbance that affects the quality of a signal.

aspect ratio    The ratio of image width to image height.

attack time    A setting within an audio digital signal processor that determines how quickly the volume will be reduced once the volume exceeds the threshold. If the attack time is too slow, then the sound will become distorted as the system adjusts.

attenuate    To reduce the amplitude (strength) of a signal or current.

Audio Coverage Uniformity measurement locations (ACUML)    The test points within a venue that have been determined to carry out the measurements for the Audio Coverage Uniformity test.

Audio Coverage Uniformity Plan (ACUP)    A stand-alone document that identifies the Audio Coverage Uniformity measurement locations for a particular venue, using the InfoComm indication symbol.

audio processor    An electronic device used to manipulate audio signals.

Audio Return Channel (ARC)    Introduced to the HDMI standard with version 1.4. ARC allows a display to send audio data upstream to a receiver or surround-sound controller, eliminating the need for a separate audio connection.

audio signal    An electrical representation of sound.

audio transduction    The process of converting acoustical energy into electrical energy or electrical energy back into acoustical energy.

Audio Video Bridging (AVB)    A standards-based audiovisual Data Link layer protocol defined under IEEE 802.1-AVB. It uses standard Ethernet cabling but requires AVB-enabled switches and network components. AVB does not require separate network infrastructure or dedicated bandwidth; AVB components automatically prioritize data. AVB was recently renamed Time-Sensitive Networking to reflect the standard’s applicability to communication among different types of devices, such as network sensors. See Time-Sensitive Networking.

audiovisual infrastructure    The physical building components that make up the pathways, supports, and architectural elements required for audiovisual technical equipment installations.

audiovisual rack    A housing unit that protects and organizes electronic equipment. The inside of a typical AV industry rack is 19 in (482.6 mm) wide. Many of the technical specifications for a rack, including size and equipment height, are determined by standards that have been established by numerous standard-setting organizations. The outside width of the rack varies from 21 to 25 in (530 to 630 mm).

authority having jurisdiction (AHJ)    An organization, office, or individual responsible for enforcing the requirements of a code or standard or for approving equipment, materials, installation, or procedure. In some areas of the world, the authority having jurisdiction is known as a regional regulatory authority.

automatic gain control (AGC)    An electronic or logic feedback circuit that maintains a constant acoustic power (gain) output in response to input variables such as signal strength or ambient noise level.

Automatic Private IP Addressing (APIPA)     A form of link-local addressing defined in the IETF standard RFC 3927. APIPA automatically assigns locally routable addresses from the reserved network 169.254.0.0/16 to devices that do not have or cannot obtain an IP address. This allows devices to communicate with other devices on the same LAN. APIPA operates at the Network layer of the OSI model and the Internet layer of the TCP/IP protocol stack.

balanced circuit    A two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground.

balun    Short for BALanced-to-UNbalanced, a transformer used to connect a balanced circuit to an unbalanced circuit. For example, a transformer used to connect a 300-ohm antenna cable (balanced) to a 75-ohm antenna cable (unbalanced).

band    A grouping or range of frequencies.

bandwidth (BW)    1. A range of frequencies. 2. A measure of the amount of data or signal that can pass through a system during a given time interval. 3. The range of frequencies used or allowed.

bandwidth (networking)    Bandwidth is the available or consumed data communication resources of a communication path, expressed in terms of bits per second. It is also called throughput or bit rate.

bandwidth limiting    The result of encoding a higher-quality signal into a lower-quality form, such as RGB converted into S-Video.

baseband    A video signal that has not been modulated.

benchmarking    The process of examining methods, techniques, and principles from peer organizations and facilities, which can be used as a basis for designing a new or renovated facility.

bend radius    The radial measure of a curve in a cable, conductor, or interconnect that defines the physical limit beyond which further bending has a measurable and/or harmful effect on the signal being transported.

bidirectional polar pattern    The shape of the region where some microphones will be most sensitive to sound from the front and rear, while rejecting sound from the top, bottom, and sides.

bill of materials (BOM)    A complete equipment list of components that must be procured in order to build the system as designed. The BOM also lists the costs associated with each aspect of designing and implementing the system.

bit    Shortened form of binary digit, symbolized by 1s and 0s. A bit is the smallest unit of digital information.

bit depth    The number of bits used to describe a sampled voltage level.

bit error rate (BER)    The total amount of error bits present in a signal after being sent across a cable. It is calculated by performing a BER test.

bit rate    The measurement of the quantity of information over time in a digital signal stream. The higher the bit rate, the better the signal quality will be. Bit rate is quantified in bits per second (bit/s or bps).

block diagram    An illustration of the signal path through a given system from sources to destinations.

Bluetooth    A wireless technology for low-cost, short-range radio links between mobile phones, computers, personal digital assistants (PDAs), and other consumer devices. It uses a short-range wireless connection wireless personal area network (WPAN), which allows devices with transceiver chips to talk to each other.

BNC connector    A professional type of video connector featuring a two-pin lock. The BNC is the most common and most professional coaxial cable connector because of its reliability and ruggedness. They are used to transport many different types of signals such as radio, frequency, component video, time code, sync, and power.

bonding    Joining conductive material by a low impedance connection, thus ensuring that they are of the same electrical potential.

boundary microphone    A microphone design where the diaphragm is placed close to a sonic “boundary” such as a wall, ceiling, or other flat surface. This prevents the acoustic reflections from the surface from mixing with the direct feed and causing phase distortions. This microphone is commonly used in conference and telepresence systems.

branch circuit    The circuit conductors between the final overcurrent device protecting the circuit and the outlets.

breaker box    See panelboard.

broadcast domain    A set of devices that can send Data Link layer frames to each other directly, without passing through a Network layer device. Broadcast traffic sent by one device in the broadcast domain is received by every other device in the domain.

building information modeling (BIM)    A data repository for building design, construction, and maintenance information, used by multiple trades on a single project.

bus    A wiring system that delivers power and data to various devices.

busbar    An electrically conductive block or bar of metal, typically copper or aluminum, that serves as a common connection for two or more circuits.

buzz    A mixture of higher-order harmonics of the 50 or 60 Hz noise (hum) originating from the AC power system and audible in the sound system.

byte (B)    An 8-bit word. The abbreviation for byte is B.

cable    An assembly of more than one conductor (wire).

cable tray    An assembly of units made of metal or other noncombustible material to provide rigid continuous support for cables.

candela    The luminous intensity of a source that emits monochromatic radiation of frequency 540×1012 Hz and has a radiant intensity in that direction of 1/683 watt per steradian. The candela has replaced the candlepower standard.

capacitance    The ability of a nonconductive material to develop an electrical charge that can distort an electrical signal.

capacitive reactance (XC)    Opposition a capacitor offers to alternating current flow. The capacitive reactance decreases with increasing frequency or, for a given frequency, the capacitive reactance decreases with increasing capacitance. The symbol for capacitive reactance is XC.

capacitor     A passive electrical component in which plates of conductive material are separated by a dielectric. For a given capacitance value, expressed in farads, a capacitor will have a greater opposition to AC current flow at lower frequencies than at higher frequencies.

cardioid polar pattern    A heart-shaped region where some microphones will be most sensitive to sound predominately from the front of the microphone diaphragm and reject sound coming from the sides and rear.

carrier    Modulated frequency that carries video or audio signal.

Category 5 (Cat 5)    The designation for 100-ohm unshielded twisted-pair (UTP) cables and associated connecting hardware whose characteristics are specified for data transmission up to 100 Mb/s (part of the EIA/TIA 568A standard).

Category 5e (Cat 5e)    An enhanced version of the Cat 5 cable standard that adds specifications for far-end crosstalk (part of the EIA/TIA 568A standard).

Category 6 (Cat 6)    A cable standard for Gigabit Ethernet and other interconnections that is backward-compatible with Category 5, Cat 5e, and Cat 3 cable (part of the EIA/TIA 568A standard). Cat 6 features more stringent specifications for crosstalk and system noise.

center tap    A connection point located halfway along the winding of a transformer or inductor.

central cluster     A single source configuration of loudspeakers. In a central cluster, the sound is coming from one point in the room. The central cluster is normally located directly above (on the proscenium), and slightly in front of, the primary microphone location.

central processing unit (CPU)    The portion of a computer system that reads and executes commands.

charged-coupled device (CCD)    A semiconductor light-sensitive device, commonly used in video and digital cameras, that converts optical images into electronic signals.

chassis    Also called a cabinet or frame, an enclosure that houses electronic equipment and is frequently electrically conductive (metal). The metal enclosure acts as a shield and is connected to the equipment grounding conductor of the AC power cable, if so equipped, to provide protection against electric shock.

chassis ground    A 0 V (zero volt) connection point of any electrically conductive chassis or enclosure surrounding an electronic device. This connection point may or may not be extended to the earth ground.

chroma    The saturation, or intensity, of a specific color. It is one of the three attributes that define a color; the other two are hue and grayscale.

chrominance    The color portion of a composite or S-Video signal.

cliff effect    The sudden loss of digital signal reception. When a digital signal is carried too far on a cable, the eye pattern will collapse, and the signal will become unreadable.

clipping    The deformation of an audio signal when a device’s peak amplitude level is exceeded.

clock adjustment    Also called timing signals, used to fine-tune the computer image. This function adjusts the clock frequencies that eliminate the vertical banding (lines) in the image.

coaxial (coax) cable    A cable consisting of a center conductor surrounded by insulating material, concentric outer conductor, and optional protective covering, all of circular cross section.

CobraNet    CobraNet is a proprietary digital audio Data Link layer protocol designed by Cirrus Logic. It uses standard Fast Ethernet cabling, switches, and other components. CobraNet signals are nonroutable.

codec    An acronym for coder/decoder. An electronic device that converts analog signals, such as video and audio signals, into digital form and compresses them to conserve bandwidth on a transmission path.

collision domain    A set of devices on a local area network (LAN) whose packets may collide with one another if they send data at the same time.

color difference signal    A signal that conveys color information such as hue and saturation in a composite format. Two such signals are needed. These color difference signals are R-Y and B-Y, sometimes referred to as Pr and Pb or Cr and Cb.

color rendering index (CRI)    The effect a light source has on the perceived color of objects relative to an incandescent source of the same correlated color temperature, which has a CRI of 100.

color temperature    The quantification of the color of “white” light, as rated on a numerical scale. Low color temperature light (~2000K) has a warm (red-ish) look, while light with a high color temperature (~6000K) has a colder (blue-ish) appearance.

combiner    In a process called multiplexing, puts signals together onto one cable, constituting a broadband signal.

common mode    1. Voltage fed in phase to both inputs of a differential amplifier. 2. The signal voltage that appears equally and, in phase, from each current carrying conductor to ground.

common-mode rejection ratio (CMRR)    The ratio of the differential voltage gain to the common-mode voltage gain; expressed in decibels.

compander    An audio processing device that combines compression and expansion.

component video    Color video in which the brightness (luminance) and color hue and saturation (chrominance) are handled independently. The red, green, and blue signals—or more commonly, the Y, R-Y, and B-Y signals—are encoded onto three wires. Because these signals are independent, processing such as chroma keying is facilitated.

composite video signal    The electrical signal that represents complete color picture information and all synchronization signals, including blanking and the deflection synchronization signals to which the color synchronization signal is added in the appropriate time relationship.

compression    1. An increase in density and pressure in air molecules. 2. A process that reduces data size.

compressor    A device that controls the overall amplitude of a signal by reducing the part of the signal that exceeds an adjustable level (threshold) set by the user. When the signal exceeds the threshold level, the overall amplitude is reduced by a ratio, also usually adjustable by the user.

compressor ratio    The compression ratio of an audio compressor determines how much the volume reduces depending on how far above the threshold the signal is.

compressor threshold    The compressor threshold sets the point at which the automatic volume reduction kicks in. When the input goes above the threshold, an audio compressor automatically reduces the volume to keep the signal from getting too loud.

condenser microphone    Also called a capacitor microphone, a microphone that transduces sound into electricity using electrostatic principles.

conductor    In electronics, a material that easily conducts an electric current because some electrons in the material are free to move.

conduit    Can mean any pathway, but in the AV and electrical industry it is a circular tube that houses cable.

cone    The most commonly used component in a loudspeaker system and found in all ranges of drivers.

constant voltage    25 V, 70 V, 100 V; a method of distributing power to loudspeakers over a large area with less loss than a typical connection would provide. This can also be called a high impedance system.

Consumer Electronic Control (CEC)    A single-wire, bidirectional serial bus that uses AV link protocols to perform remote-control functions. It is an optional feature of the HDMI specification that allows for system-level automation when all devices in an AV system support it.

contact closure    A contact closure is the simplest form of remote-control communication. It is a switch. This type of control point operates a device by opening or closing an electrical current or voltage loop. It has the most basic protocol language: “on” (closed circuit) or “off” (open circuit).

content delivery network (CDN)    A distributed network of caching servers that can provide hosted unicast distribution of media for an organization. They are most often utilized by organizations whose content is in high demand.

contrast    Absolute difference in luminance between the peak white and black levels, where white and black luminance is displayed simultaneously.

contrast ratio    Describes the dynamic video range of a display device as a numeric relationship between the brightest color (typically white) and the darkest color (typically black) that the system is capable of producing. Two methods are used to specify contrast ratio; the full on/full off method describes the dynamic contrast ratio, and the ANSI measures the static contrast ratio.

control system    A subsystem that simplifies the operation of an AV system.

correlated color temperature (CCT)    The color appearance of a light source as measured on the Kelvin scale.

coverage pattern    The predictable pattern of sound energy that every loudspeaker emits. The coverage pattern is based on the frequency of the sounds and the physical size of the loudspeaker.

critical distance (Dc)    The point where the sound pressure level of the direct reverberant sound field are equal.

critical path schedule    Reveals the interdependence of activities and assesses resource and time requirements and trade-offs. It also determines the project’s completion date and provides the capability to evaluate activity performance.

crossover    Separates the audio signal into different frequency groupings and routes the appropriate material to the loudspeaker or amplifier to ensure that the individual loudspeaker components receive program signals that are within their optimal frequency range.

crosstalk    Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.

current    The amount of electrical charge that is flowing in a circuit, measured in amperes.

curvature of field    A blurry appearance around the edge of an otherwise in-focus object (or the reverse) when the velocity of light going through the lens is different at the edges than at the center of the surface. Curvature of field is due to the lens design.

Dante    A proprietary digital audio Network layer protocol designed by Audinate. Dante sends audio information as Internet Protocol (IP) packets. It is fully routable over IP networks using standard Ethernet switches, routers, and other components. Dante traffic requires no separate infrastructure; it can coexist with other data traffic. Dante controller software manages data prioritization and audio routes.

dB SPL    A measure of sound pressure level represented in dynes per centimeter squared. Its reference, 0 dB SPL, equals 0.0002 dynes/cm². dB SPL is used as a measure of acoustical sound pressure levels and is a 20-log function.

decibel (dB)    A base-10 logarithmic relationship of a power ratio between two numbers. This is used for quantifying differences in voltage, distance, and sound pressure as they relate to power.

delay    An audio signal-processing device or circuit used to retard the speed of transmission on one or more audio signals or frequencies.

demodulator    An electronic device that removes information from a modulated signal.

depth of field    The area in front of a camera lens that is in focus from the closest item to the camera to the item farthest away.

detail drawing    A detail drawing enlarges small items to show how they must be installed. They depict items too small to see at the project’s typical drawing scale.

dielectric constant    Describes the ability of a material between two conductors to store an electrical charge. Dielectric strength is determined by the material’s type and thickness and is the amount of voltage that insulation can stand before it breaks down.

differential mode    1. Voltage fed out of phase to both inputs of a differential amplifier. 2. Signals measurable between or among active circuit conductors feeding the load but not between the equipment grounding conductor or associated signal reference structure and the active circuit conductors.

differentiated service (DiffServ)    A network quality-of-service strategy wherein data from specific applications or protocols are assigned a class of service. Flows assigned a high priority are given preferential treatment at the router, but delivery is not guaranteed.

diffusion    The scattering or random redistribution of a sound wave from a surface. Diffusion occurs when surfaces are at least as long as the sound wavelengths but not more than four times as long.

digital media player    Digital media players are devices that allow users to play back or stream audio and video content from digital media servers, the Internet, or computer hard drives.

digital-only token (DOT)    A digital flag that is embedded onto digital sources, such as Blu-ray Discs. Its purpose is to limit the availability or quality of HD content on the component output of a media player.

digital signage    Digital signage is customized content shown on strategically located displays intended to attract specific types of viewers. It is sometimes referred to as dynamic signage to differentiate it from large-format static signs. Digital signage is displayed on LCD and LED panels, kiosks, and projection screens. These displays are placed in public spaces, museums, stadiums, corporate and educational buildings, retail stores, hotels, restaurants, and other locations.

digital signage media player    A hardware device or computer server used to store and forward or play back digital signage content on display screens. Some commercial digital signage displays have integrated media players on a chip. Digital signage players are often located in close proximity to the display screen but may also be located remotely. Network-ready media players enable the control and management of content remotely.

digital signage template    Customizable layouts used for standardizing content across all displays on the network. They enable multiple messages or content from multiple sources to be displayed on a screen by presenting the information in zones.

digital signal processor (DSP)    Combines processor functions such as mixers, limiters, and equalizers, typically into a single device.

digital-to-analog converter    An electronic device that converts digital signals into analog form.

direct couple    A loudspeaker system in which the amplifier is connected directly to the voice coil wires of the loudspeaker.

direct current (DC)    Electricity that maintains a steady flow and does not reverse direction, unlike alternating current (AC). It is usually produced by batteries, AC-to-DC transformers, and power supplies.

direct sound    Also known as near-field, sound that is not colored by room reflections.

direct view display    Houses the light-producing elements and screen in one piece of equipment.

directivity    The specific coverage pattern that designers must consider when determining the placement of loudspeakers required to provide full coverage for all the listeners within a space.

dispersion    An effect that can be seen when a white light beam passes through a triangular prism. The different wavelengths of light refract at different angles, dispersing the light into its individual components.

Display Data Channel (DDC)    The electrical channel that EDID and HDCP use for communication between a video card and a display. It is a collection of protocols maintained as a standard by the Video Electronics Standards Association (VESA).

DisplayID    A standard developed by VESA outlining how video display data is structured to describe its performance and capabilities when communicating with other devices. By structuring data in a flexible, modular way, DisplayID enables devices to identify new display resolutions, refresh rates, audio standards, and other formats as they become available. For example, the standard can support a single image segmented across tiled displays using multiple video processors.

DisplayPort    A digital display interface developed by the Video Electronics Standards Association (VESA) to replace VGA and DVI and used to connect a video source to a display device. It can also carry audio, USB, and other data.

distributed sound system    A sound system using multiple loudspeakers separated by distance. It typically operates in a lower sound pressure level than a high-pressure system. The loudspeakers are most often suspended over the heads of the listeners.

distribution amplifier (DA)    An active device used to split one input into multiple outputs, while keeping each output isolated and the signal level constant.

diversity receiver    A diversity receiver is an RF receiver that uses a pair of antennas to receive a transmitted RF signal. Diversity receivers constantly calculate phase differences between signals to dynamically shift between the two antennas and avoid cancellation.

DLP    Digital Light Processing by Texas Instruments. A projection system that has technology based on the digital micromirror device (DMD). It uses thousands of microscopic mirrors on a chip focused through an optical system to display images on the screen.

Domain Name System (DNS)    A hierarchical, distributed database that maps names to data such as IP addresses. A DNS server keeps track of all the equipment on the network and matches the equipment names so they can easily be located on the network or integrated into control and monitoring systems. See reserve DHCP.

dome    A type of loudspeaker driver construction. Fabric or woven materials are used to create a dome-shaped diaphragm, and the coil is attached to the edge of the diaphragm.

driver    In audio, an individual loudspeaker unit.

dual channel    In a measurement scenario, indicates that two inputs are used for measuring something under test. The two channels used are a test reference signal and a measured signal.

DVD    Digital Video Disc or Digital Versatile Disc. This is an optical storage medium for data or video.

DVI    Digital Visual Interface. This is a connection method from a source (typically a computer) and a display device that can allow for direct digital transfer of data. The connection is limited to a distance of 5 meters (16 feet) for resolutions up to 1920×1200. Lower resolutions such as 1280×1024 can reach up to 15 meters (49 feet). DVI has largely been replaced by HDMI, DisplayPort, and other formats.

Dynamic Host Configuration Protocol (DHCP)    An IP addressing scheme that allows network administrators to automate address assignment.

dynamic microphone    A pressure-sensitive microphone of moving-coil design that transduces sound into electricity using electromagnetic principles.

dynamic range    The difference between the loudest and quietest levels of an audio signal.

early reflected sound    Sound created by sound waves that are reflected (bounced) off surfaces between the source and the listener. The sound waves arrive at the listener’s ear closely on the heels of the direct sound wave.

echo    A reflected version of sound energy acoustically, or a duplicated version of a signal electronically, that arrives to the listener with sufficient delay and separation from the original signal to allow the delayed signal to be perceived distinctly and later in time from the original signal.

echo cancellation    A means of eliminating echo from an audio signal path.

electret microphone    A type of condenser microphone. It has prepolarized material, called electret, which is applied to the microphone’s diaphragm or backplate.

electrical service    The conductors and equipment for delivering energy from the electricity supply system to the wiring system of the site served.

electromagnetic interference (EMI)    Disruption of operation of a circuit (noise) due to the effects of interference from electric and/or magnetic fields.

elevation drawing    A two-dimensional view of a single surface. It is commonly used for creating a true picture of what a surface will look like.

emissive technology    Any display device that emits light to create an image.

encoded    A signal that has been compressed into another form to reduce size or complexity, as in a composite video signal.

energy management plan    A document that details a systematic approach to implementing the most effective power consumption methods and procedures to achieve and maintain optimum energy usage.

equalizer    Electronic equipment that adjusts or corrects the frequency characteristics of a signal.

equipment grounding    The connection to ground (earth), or to a conductive body that extends that ground connection, of all normally noncurrent-carrying conductive materials enclosing electrical conductors or equipment or forming part of such equipment. The purpose is to limit any voltage potential between the equipment and earth.

equipment grounding conductor (EGC)    The conductive path installed to connect normally noncurrent-carrying metal parts of equipment together and to the system’s grounded conductor, to the grounding electrode conductor, or to both.

equipment rack    A centralized housing unit that protects and organizes electronic equipment.

equivalent acoustic distance (EAD)    The farthest distance one can go from the source without the need for sound amplification or reinforcement to maintain good speech intelligibility. It is a design parameter dependent on the level of the presenter and the noise level in the room.

ergonomics    Also known as human factors or human factors engineering. This is the scientific study of the way people interact with a system. It focuses on effectiveness, efficiency, reducing errors, increasing productivity, improving safety, reducing fatigue and stress, increasing comfort, increasing user acceptance, increasing job satisfaction, and improving quality of life.

Ethernet    A set of network cabling and network access protocol standards administered by the 802.3 subcommittee of the IEEE. Ethernet signals are transmitted serially, one bit at a time, over the shared signal channel to every attached station.

EtherSound    A proprietary digital audio Data Link layer protocol designed by Digigram. It uses standard 100 Mbps or 1 Gbps Ethernet cabling, switches, and other components. EtherSound signals are nonroutable.

expander    An audio processor that comes in two types: a downward expander and as a part of a compander.

extended display identification data (EDID)    A data structure within a sink that is used to describe the sink’s capabilities to a source. These capabilities include native resolution, color space information, and audio type (mono or stereo).

external configuration    Refers to the ability of one device to configure other devices and subsystems.

far field    The sound field distant enough from the sound source so the SPL decreases by 6 dB for each doubling of the distance from the source.

farthest viewer    The viewer positioned at the farthest distance from the screen as defined by the viewing area.

feedback    1. In audio, unwanted noise caused by the loop of an audio system’s output back to its input. 2. In a control system, data supplied to give an indication of status, such as on or off.

feedback stability margin (FSM)    Extra margin that represents additional gain that a sound system may need. It is the possibility of feedback due to the nonlinearity across the frequency band of a sound system.

fiber optic    A technology that uses glass or plastic threads or wires to transmit information.

field    In video, one-half of a video frame containing every other line of information. Each standard video frame contains two interlaced fields.

filter    Removes or passes certain frequencies from a signal.

firewall    Any technology, hardware, or software that protects a network by preventing intrusion by unauthorized users and/or regulating traffic permitted to enter or exit the network. A firewall controls what traffic may pass through a router connecting one network to another. Firewalls control access across any network boundaries, including between an enterprise network and the Internet or between local area networks (LANs) within an enterprise.

firmware    A type of software that has been permanently stored in a piece of hardware.

fixture    A fixture is a lamp housing that is mounted or fixed in place.

flex life    The number of times a cable can be bent before it breaks. A wire with more strands or twists per inch will have a greater flex life than one with a lower number of strands or fewer twists per inch.

focal length (FL)    1. The distance, in millimeters, between the center of a lens and the point where the image comes into focus. 2. The value given to a lens, stated in inches or millimeters. The shorter the focal length, the wider the angle of the image will be.

footcandle (fc)    An English unit of measure expressing the intensity of light illuminating an object. A footcandle equals the illumination from one candle falling on a surface of 1 square foot at a distance of 1 foot.

footlambert (fl)    The footlambert (fl) is a U.S. customary unit of measurement for luminance. It is equal to 1/pi candela per square foot.

frame rate    The number of frames sent from a display source per second.

frequency    The number of complete cycles in a specified period of time. It is formerly expressed as cycles per second (cps), now specified as hertz (Hz).

frequency domain    A signal viewed as amplitude versus frequency is in the frequency domain. This allows you to view the amount of energy present at different frequencies.

frequency response    The amplitude response versus frequency for a given device.

Fresnel lens    A flat glass or acrylic lens in which the curvature of a normal lens surface has been collapsed in such a way that concentric circles are impressed on the lens surface. A Fresnel lens is often used for the condenser lens in overhead projectors, in rear-screen projection systems, and in studio spotlights.

front-screen projection    A system that employs a light-reflecting screen for use when the image will be projected from a source in front of the screen.

full-duplex communication    A form of bidirectional data transmission in which multiple messages may travel on the same medium simultaneously.

full HD    An HDTV high-definition video mode characterized by 1080 horizontal lines of vertical resolution and progressive scanning. It is commonly notated as 1080p.

fundamental frequency    Known as pure tone, the lowest frequency in a harmonic series.

gain    1. Electronic signal amplification. 2. The ability of a projection screen to concentrate light.

gain control    A gain control is an electronic adjustment through which the operator can increase or decrease the amplitude of a defined signal element.

gain-sharing automatic mixers    A gain-sharing automatic mixer is an audio mixer that automatically turns up microphone channels that are in use and turns down microphone channels that are not being used.

gate    An audio processor that allows signals to pass only above a certain setting or threshold.

gated automatic mixer    An audio mixer that turns microphone channels either “on” or “off” automatically.

gateway    The highest router in the hierarchy of routers. It connects a local network to an outside network, and all traffic must travel through it. A gateway will pass traffic to the routers below, and the routers below look to the gateway to find names (DNS addresses) that are not found on the local network.

gauge    A thickness or diameter of a wire.

genlock    To lock the synchronization signals of multiple devices to a single source.

graphic equalizer    Equalizer with an interface that has a graph comparing amplitude on the vertical with frequency on the horizontal.

graphical user interface (GUI)    Often pronounced “gooey”; provides a visual representation of the system features and functions.

graphics adapter    Commonly referred to as a video card, outputs computer signals.

grayscale    The brightness and darkness of a color. It is sometimes called value. It is one of the three attributes of color; the other two are hue and chroma.

grayscale test pattern    Displays the broadest range of intensities between black and white on the screen.

ground    1. The earth. 2. In the context of an electrical circuit, the earth or some conductive body that extends the ground (earth) connection. 3. In the context of electronics, the 0 V (zero volt) circuit reference point. This electronic circuit reference point may or may not have a connection to earth.

ground fault    1. An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and a normally noncurrent-carrying conductor, metallic enclosure, metallic raceway, metallic equipment, or earth. 2. The electrical connection between any ungrounded conductor of the electrical system and any noncurrent-carrying metal object.

ground loop    An electrically conductive loop that has two or more ground reference connections. The loop can be detrimental when the reference connections are at different potentials, which causes current flow within the loop.

ground plane    A continuous conductive area. The fundamental property of a ground plane is that every point on its surface is at the same potential (low impedance) at all frequencies of concern.

ground potential    A point of no potential in a circuit.

ground reference    The 0 V (zero volt) reference point for a circuit.

grounded conductor    A system or circuit conductor that is intentionally grounded.

ground-fault circuit interrupter (GFCI)    A safety device that deenergizes a circuit (or a portion of that circuit) within an established period of time when a current to ground exceeds the values established for a Class A device. Class A GFCIs trip when the current to ground is 6 mA or higher; they do not trip when the current to ground is less than 4 mA.

ground-fault current path    An electrically conductive path from the point of a ground fault on a wiring system through normally noncurrent-carrying conductors, equipment, or earth to the electrical supply source.

grounding    Connecting to ground or to a conductive body that extends the ground connection. The connected connection is referred to as grounded.

grounding conductor    A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

grounding electrode    A conducting object through which a direct connection to earth is established.

grounding electrode conductor    The conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.

group management protocol (GMP)    Allows a host to inform its neighboring routers of its desire to start or stop receiving multicast transmissions. Without a GMP, multicast traffic is broadcast to every client device on the network segment, impeding other network traffic and overtaxing device CPUs.

group of pictures (GoP)    A set of successive frames that are required to display a complete series in a digital AV signal. It includes the visible picture, timing/sync information, and compression frames.

half duplex    A form of data transmission in which only one network node at a time sends data.

harmonic distortion    A multiple of a fundamental frequency that does not exist in the original signal.

harmonics    Higher-frequency sound waves that blend with the fundamental frequency.

HD-15 connector    An HD-15 connector, sometimes called a VGA connector, is a video connector that is typically associated with the output of a computer graphics card. It has three rows of five pins, which carry analog red, green, blue, and sync signals along with display data channel information.

HDCP key    A long number that a program uses to verify authenticity and encode/decode content. HDCP processes use multiple types of keys. These keys are strongly protected by Digital Content Protection, LLC.

HDCP receiver    A device that can receive and decode the HDCP signals. A television is an example of a receiver.

HDCP repeater    A device that can receive HDCP signals and transmit them to another device, such as a switcher or distribution amplifier.

HDCP sink    A device that receives and decodes the HDCP signals.

HDCP source    A device that sends HDCP-encoded signals and content.

HDCP transmitter    A device that can send HDCP-encoded signals and content. A Blu-ray Disc player is an example of an HDCP transmitter.

HDMI Ethernet Audio Control (HEAC)    In HDMI, the combining of HEC (HDMI Ethernet Channel) and ARC (Audio Return Channel) into one port or cable. See HDMI Ethernet Channel (HEC) and Audio Return Channel (ARC).

HDMI Ethernet Channel (HEC)    Consolidates video, audio, and data streams into a single HDMI cable. A dedicated data channel enables high-speed, bi-directional networking to support future IP solutions and allow multiple devices to share an Internet connection.

HDTV    High-definition television.

headend    The equipment located at the start of a cable distribution system where the signals are processed and combined prior to distribution.

headroom    The difference in dB SPL between peak- and average-level performance of an audio system.

heat load    Heat load is the heat that is generated and released by a piece of electronic equipment. It is measured in British thermal units.

heat sink    A device that absorbs and dissipates heat produced by an electrical component.

hemispheric polar pattern    The dome shape of the region that some microphones will be most sensitive to sound. This pattern is used for boundary microphones.

hertz (Hz)    Cycles per second of an electrical signal.

High-Bandwidth Digital Content Protection (HDCP)    A form of encryption developed by Intel to control digital audio and video content as it travels across Digital Video Interface (DVI) or High Definition Multimedia Interface (HDMI) connections. It prevents transmission or interception of nonencrypted HD content.

High Definition Multimedia Interface (HDMI)    A point-to-point connection between video devices for all-digital video and audio. HDMI signals include audio, control, and digital asset rights management information. It is fully compatible with DVI.

high-pass filter    A circuit that allows signals above a specified frequency to pass unaltered while simultaneously attenuating frequencies below the specified limit.

hiss    Broadband higher-frequency noise typically associated with poor audio system gain structure.

horn    A loudspeaker that reproduces mid to high frequencies.

hot plug    A low-level signal sent by a source that indicates whether a sink or display is connected.

hue    The attribute of a color that represents a red, a purple, a green, and so on. It is one of the three attributes that define color; the other two are grayscale and chroma.

hum    Undesirable 50 to 60 Hz noise emanating from a sound system or evidenced by a rolling hum bar on a display.

IEEE    The Institute of Electrical and Electronics Engineers.

illuminance    Light falling on a surface, measured in lux (lx) or footcandle (ft-c or fc) [1 lux = 0.09 fc]. It is not visible to human eye other than in the form of reflected luminance.

image constraint token (ICT)    A digital flag built into some digital video sources. It prevents unauthorized copies of content from appearing on a sink device. This encryption scheme ensures that high-definition video can be viewed only on HDCP-enabled sinks.

image resolution    Image resolution is the total number of pixels of the display. It is normally expressed as a ratio of horizontal pixels to vertical pixels.

imager    A light-sensitive electronic chip behind a video camera’s lens made up of thousands of sensors, called pixels, which convert the light input into an electrical output. In normal operation, an imager will output a frame of captured video at the frame rate of the video standard.

impedance (Z)    The total opposition to current flow in an AC circuit. Like a DC circuit, it contains resistance, but it also includes forces that oppose changes in the current (inductive reactance) and voltage (capacitive reactance). Impedance takes into account all three of these factors. It is measured in ohms, and its symbol is Z.

impedance matching    Having an impedance value on an input that an output is expecting. It does not necessarily mean having comparable impedances on an input and an output.

impedance meter    Used to measure true impedance of an electrical circuit.

inductance (L)    The property of a conductor that opposes any change in current, represented by the symbol L and measured in henries (H).

induction    The influence exerted on a conductor by the movement of a magnetic field.

inductive reactance (X_L)    Opposition to the current flow offered by the inductance of a circuit. It is dependent on frequency and inductance. Its symbol is X_L.

InfoFrames    Structured packets of data that carry information regarding aspects of audio and video transmission, as defined by the EIA/CEA-861B standard. Using this structure, a frame-by-frame summary is sent to the display, permitting selection of appropriate display modes automatically. InfoFrames typically include auxiliary video information, generic vendor-specific source product description, MPEG, and audio information.

infrared (IR)     A range of light frequencies used to send information. IR transmission requires line-of-sight between transmitter and receiver. Infrared signals may be either wired or wireless.

input    A connection point that receives information from another piece of equipment.

I/O port    Typically used for input binary signals to a control system to indicate the state of a connected device, such as active or inactive, on or off, or connected or not connected.

insulation    Also known as the dielectric, material applied to a conductor that is used to isolate the flow of electric current between conductors and to provide protection to the conductor.

Integrated Services Digital Network (ISDN)    A communications standard for transmitting voice, video, and data over digital phone lines or the traditional telephone network. Common applications of ISDN include telecommuting, Internet access, video conferencing, and data networking.

intelligibility    A sound system’s ability to produce an accurate reproduction of sound allowing listeners to identify words and sentence structure.

Internet Corporation for Assigned Names and Numbers (ICANN)    A nonprofit organization chartered to oversee several Internet-related tasks. ICANN manages Domain Name System (DNS) policy, including the top-level domain space for the Internet.

Internet Group Management Protocol (IGMP)    The IPv4 group management protocol. IGMPv1 allowed individual clients to subscribe to a multicast channel. IGMPv2 and IGMPv3 added the ability to unsubscribe from a multicast channel.

interlaced scanning    The scanning process that combines odd and even fields of video to produce a full frame of video signal.

internal configuration    Refers to the setup and customization of a management or control device.

Internet Protocol (IP)    A TCP/IP protocol defined in the IETF standard RFC 791. IP defines rules for addressing, packaging, fragmenting, and routing data sent across an IP network. IP falls under the Internet layer of the TCP/IP protocol stack and the Network layer of the OSI model.

Internet Protocol Television (IPTV)    A system that delivers television services over a packet-switched network such as a LAN or the Internet.

inverse square law    The law of physics stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.

IP    See Internet Protocol (IP).

IR    See infrared (IR).

isolated ground (IG)     An equipment grounding method permitted by the NEC for reducing electrical noise (electromagnetic interference) on the grounding circuit. The isolation between IG receptacles and circuits and the normal equipment grounding is maintained up to the point of the service entrance (or a separately derived system) where the grounded (neutral) conductor, equipment grounding, and isolated equipment grounding conductor are bonded together and to earth ground.

isolated grounding circuit    A circuit that allows an equipment enclosure to be isolated from the raceway containing circuits, supplying only that equipment by one or more listed nonmetallic raceway fittings. The equipment is grounded via an insulated grounding conductor.

isolated receptacle    A receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means. Isolated receptacles are identified by a triangle engraved on the face and are available in standard colors. The receptacle (and so the equipment plugged into the receptacle) is grounded via an insulated grounding conductor.

jacket    Outside covering used to protect cable wires and their shielding.

junction box    A metal or plastic enclosure for enclosing the junction of electrical wires and cables. A junction box can be used as a termination point with a custom connector plate or interface plate. A junction box can also be installed and used as a pull box for longer cable runs.

keystone error    The trapezoidal distortion of a square-cornered image because of the optical effect of the projection device being located in an improper position with respect to the screen.

lamp    The bulb or source of light output.

latency    Response time of the network. It is expressed as the amount of time in milliseconds between a data packet’s transmission from the source application and its presentation to the destination application.

lavalier    A small microphone designed to be worn either around the neck or clipped to apparel.

Law of Conservation of Energy    States that the total energy cannot be created or destroyed. Energy can be transformed from one form to another and transferred from one body to another, but the total amount of energy remains constant.

least favored viewer (LFV)    The farthest usable seat from the image. The LFV depends on the viewing angle toward the screen, image size, and content being displayed.

lenticular    A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles.

lighting fixture    An installed lighting instrument.

limiter    An audio signal processor that functions like a compressor except that signals exceeding the threshold level are reduced at ratios of 10:1 or greater.

limiter ratio    Defines how much the limiter will compress signals that exceed its threshold. The limiter compresses only the portion of the signal that exceeds its threshold, after the signal has already passed through the compressor.

limiter threshold    Defines which portions of the signal the limiter will affect. All decibel levels below or equal to the threshold will pass through the limiter unchanged. All signals above the threshold will be compressed.

line driver    Used for gain and peaking to compensate for signal attenuation created by cable resistance for longer cable runs.

line level    The strength of an audio signal. Line levels perform signal routing and processing between audio components, such as loudspeakers.

liquid crystal display (LCD)    A video display that uses liquid crystals to produce an image. These devices do not emit light directly.

liquid crystal on silicon (LCoS)    A reflective, fixed-resolution LCD imaging technology. LCoS panels resemble LCD panels in size and function. A liquid crystal layer is applied inside an LCoS panel to a reflective complementary metal-oxide semiconductor (CMOS) mirror substrate. The LCoS chip has a fixed matrix of pixels, each backed by a mirrored surface.

listed    Equipment, materials, or services included in a list published by a Nationally Recognized Testing Laboratory (NRTL), such as Underwriters Laboratories (UL), that is acceptable to the authority having jurisdiction (AHJ).

load center    An electrical industry term used to identify a lighting and appliance panelboard designed for use in residential and light-commercial applications.

local area network (LAN)    A computer network limited to the immediate area, usually the same building or floor of a building. A LAN connects devices within a small geographical area, such as a building or campus.

local monitor    A device used to monitor the output of a signal from a system or other device in the local vicinity.

logarithm    The exponent of base-10 that equals the value of a number.

logic network diagram    A tool that helps sequence and ultimately schedule the project’s activities and milestones. It helps determine whether all the activities necessary to complete the program are present.

looping scheme    Features electronics with the ability of passing on the video signal to another device. Looping distributes a video signal to multiple devices (usually displays) simultaneously.

lossless compression    A process that retains the original quality of a file after it has been compressed and decompressed.

lossy compression    A form of compression that gives an approximation of the original data by eliminating redundant or unnecessary information.

loudspeaker    A transducer that converts electrical energy into acoustical energy. A loudspeaker is basically a driver within an enclosure.

loudspeaker circuit    A group of wired loudspeakers. Each loudspeaker in the circuit will have an impedance value.

low-pass filter    A circuit that allows signals below a specified frequency to pass unaltered while simultaneously attenuating frequencies above the specified limit.

low voltage    An ambiguous term. It may mean less than 70 V AC to an AV contractor, while an electrician may use the same term to describe circuits less than 600 V AC. The term may also be determined by the authority having jurisdiction (AHJ).

lumen    A measure of the light quantity emitted from a constant light source across 1 square meter.

Luminaire    A complete lighting instrument comprised of a light source, globe, reflector, and housing.

luminance (Y)    Also called luma, part of a bandwidth-limited video signal combining synchronization information and brightness information. Its symbol is Y.

lux    A contraction of the words luminance and flux. 10.7 lux is equal to 1 footcandle.

MAC address     The actual hardware address, or number, of an NIC device. Each device has a globally unique Media Access Control (MAC) address to identify its connection on the network.

matrix decoder    A decoder that produces red, green, and blue from Y, R-Y, and B-Y.

matrix switcher    An electronic device with multiple inputs and outputs. The matrix allows any input to be connected to any one, several, or all the outputs.

matte-white screen    A screen that evenly disperses light 180 degrees uniformly, both horizontally and vertically, creating a wide viewing cone and wide viewing angle.

maximum transmission unit (MTU)    The size in bytes of the largest frame that can pass over a Data Link layer connection. Any header information must be included within the MTU.

mechanical switcher    A switch that mechanically connects cables or circuits. It functions like a wall switch, meaning there is a mechanical connection or disconnection between two conductors.

meshed topology    Where every local area network (LAN) connects to every other LAN.

mic level    A very low line-level signal. It creates only a few millivolts of electrical energy.

microphone sensitivity    A specification that indicates the electrical output of a microphone when it is subjected to a known sound pressure level.

middleware    Software that provides services to applications that aren’t available from the operating system. In a streaming system, for example, middleware software may perform transcoding, compression, or remote access authentication functions, enabling users to access content from diverse endpoints.

midrange    A loudspeaker that reproduces midrange frequencies, typically 300 Hz to 8,000 Hz.

milestone    A significant or key event in the project, usually the completion of a major deliverable or the occurrence of an important event. It can often be associated with payment milestones, and client approvals.

millwork    Items that are custom cut for the project, such as moldings or trim.

mixer    A device for blending multiple audio sources.

mix-minus system    A type of speech reinforcement system that allows both meeting presenters and participants to be heard. Each loudspeaker is given a separate subsystem, which mixes the microphone signals, minus the closest microphone.

Mobile High-Definition Link (MHL)    Originally a standard audio/video interface for connecting mobile electronics to high-definition televisions and audio receivers. The latest version, superMHL, is capable of 36 Gbps and up to 8K resolution, making it a possible option for more general AV applications.

modular connector    A connector used with four, six, or eight pins. Common modular connectors are RJ-11 and RJ-45 (8P8C).

modulator    A device that converts composite or S-Video signals, along with corresponding audio signals, into modulated signals on a carrier channel.

Multicast Listener Discovery (MLD)    The IPv6 group management protocol. Multicast is natively supported by IPv6; any IPv6 router will support MLD. MLDv1 performs roughly the same functions as IGMPv2, and MLDv2 supports roughly the same functions as IGMPv3.

multicast streaming    A one-to-many transmission, meaning one server sends out a single stream that can then be accessed by multiple clients. Class D IP addresses are set aside for multicast transmissions.

multimeter    A multipurpose test instrument with a number of different ranges for measuring current, voltage, and resistance.

multiplexing    The process used by the combiner to put together a number of modulated signals.

multipoint    Also called continuous presence, videoconferencing that links many sites to a common gateway service, allowing all sites to see, hear, and interact at the same time. Multipoint requires a bridge or bridging service.

Multi-Protocol Label Switching (MPLS)    A networking protocol that allows any combination of Data Link layer protocols to be transported over any type of Network layer. MPLS routes data by examining each packet’s MPLS label without examining packet contents. Implementing MPLS improves interoperability and routing speed.

native resolution    The number of rows of horizontal and vertical pixels that create the picture. The native resolution describes the actual resolution of the imaging device and not the resolution of the delivery signal.

near-field    The sound field close to the sound source that has not been colored by room reflections. This is also known as direct sound.

needed acoustic gain (NAG)    The gain the sound system requires to achieve an equivalent acoustic level at the farthest listener equal to what the nearest listener would hear without sound reinforcement.

needs analysis    A needs analysis, also referred to as the programming phase, consists of identifying the activities that the end users need to perform and then developing the functional descriptions of the systems that support those needs.

Network Address Translation (NAT)    Any method of altering IP address information in IP packet headers as the packet traverses a routing device. NAT is typically implemented as part of a firewall strategy. The most common form of NAT is Port Address Translation (PAT).

network bridge    Connects two different types of networks. It translates one network protocol to another protocol. An example of a bridge is a computer modem. A cable modem converts, or bridges, the Ethernet protocol to a cable TV protocol.

network interface card (NIC)    An interface that allows you to connect a device to a network. Many NICs are now integrated into the device’s main circuitry.

network segment    A network segment is any single section of a network that is physically separated from the rest of the network by a networking device such as a switch, router, or hub. A segment may contain one or more hosts.

network switch    Connects multiple devices together so they can communicate with the other devices that are also connected to the switch. As each device is connected, the switch collects and stores the MAC address of the device that it communicates with. When one device wants to communicate with a second device, the switch looks up the destination device’s location in its memory and then sends the information to its destination.

network topology    The physical connection that aids in the communication between devices in an area network.

neutral conductor    See grounded conductor.

nit    The metric unit for screen or surface brightness.

noise    Any electrical signal present in a circuit other than the desired signal.

noise criterion (NC) rating    Developed to establish satisfactory conditions for speech intelligibility and general living environments. Measurements are taken at eight center octave frequencies from 63 to 8,000 Hz and plotted against a standardized curve.

noise-masking system    Introduces background noise to hinder communication and increase privacy. These are also sometimes called sound-masking or speech-privacy systems.

noisy ground    An electrical connection to a ground point that produces or injects spurious voltages into the computer system through the connection to ground (IEEE Std. 142-1991).

nominal impedance    The low point in the usable frequency area in a loudspeaker.

notch filter    A filter that notches out, or eliminates, a specific band of frequencies.

number of open microphones (NOM)    Takes into account the increased possibility of feedback by adding additional live microphones in a space. Each time the number of open microphones is doubled, you lose 3 dB of gain before feedback.

Nyquist-Shannon Sampling Theorem    States that an analog signal can be reconstructed if it is encoded using a sampling rate that is greater than twice the highest frequency sampled. For example, since the range of human hearing extends to 20 kHz, the sampling rate for digital audio should be greater than 40 kHz.

octave    A band, or group, of frequencies. The relationship of the frequencies is such that the lowest frequency is half the highest. 200 Hz to 400 Hz is an octave; 4,000 Hz to 8,000 Hz is an octave; and so on.

Ohm’s law    A law that defines the relationship between current, voltage, and resistance in an electrical circuit as proportional to applied voltage and inversely proportional to resistance. The formula is I=V/R, where I is the current (in amps), V is the voltage (in volts), and R is the resistance (in ohms).

omnidirectional    Describes the shape of the area for microphones that have equal sensitivity to sound from nearly all directions.

on-axis    The center point of a screen, perpendicular to the viewing area for a displayed image. This is considered to be the best location for viewing.

organic light-emitting display (OLED)    Consists of layers of organic compounds that emit light when an electric current flows through it. There are separate organic layers for red, green, and blue.

oscilloscope    A test device that allows measurement of electronic signals by displaying the waveform on a CRT.

OSI model     Open Systems Interconnection model. This is a reference model developed by ISO in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. Network communication protocols fall into seven categories, or layers.

overcurrent    Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, a short circuit, or a ground fault.

overcurrent protection device    A safety device designed to open a circuit if the current reaches a value that causes excessive or dangerous temperatures in conductors or conductor insulation. Examples are circuit breakers and fuses.

packet filtering    A technique that uses rules to determine whether a data packet will be allowed to pass through a firewall. Rules are configured by the network administrator and implemented based on the protocol header of each packet.

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.

parallel circuit    A circuit in which the voltage is the same across each load, but the current divides and takes all the available paths and returns to the source.

parametric equalizer    Allows discrete selection of a center frequency and adjustment of the width of the frequency range that will be affected. This can allow for precise manipulation with minimal impact of adjacent frequencies.

peak    The highest level of signal strength, determined by the height of the signal’s waveform.

peaking    An adjustment method that allows compensation for high-frequency loss in cables.

peaking control    Electronic adjustments within a video component that can be used to compensate for system losses, particularly in cable capacitance.

permissible area    The maximum amount of space that cables should occupy inside the conduit.

phantom power    A DC power source available in various voltages.

phase    A particular value of time for any periodic function. For a point on a sine wave, it is a measure of that point’s distance from the most recent positive-going zero crossing of the waveform. It is measured in degrees; 0 to 360 degrees is a complete cycle.

phono    The European name for an RCA connector.

phosphor    The substance that glows when struck by an electron beam, providing the image in a CRT. The higher the quality of the phosphor, the brighter and more vivid the image.

pink noise    A sound that has equal energy (constant power) in each 1/3-octave band.

pink noise generator (PNG)    Intended to provide an unintelligible noise source that represents an equal amount of energy per octave through a sound system. It is commonly used to evaluate and align a sound system in an environment.

pixel    A combination of two words, picture and element. The smallest element used to build a digital image.

plan view    A plan view is a drawing of a space from the “top view,” taken directly from above. Examples include a floor plan and site plan.

plane of screen    Identification of image position on a plan or drawing relative to other plotted locations. It is a notional line, whether in plan view or elevation, that aligns with the front surface of the screen (that is, image position) used as a datum to define viewers’ relative positions.

plasma display panel (PDP)    A direct-view display consisting of an array of cells, known as pixels, which are composed of three subpixels, corresponding to the colors red, green, and blue. Gas in the plasma state is used to react with phosphors in each subpixel to produce colored light (red, green, or blue) from a phosphor in each subpixel.

playback system    A playback system is a music reinforcement system that has a wide frequency response bandwidth and is capable of high sound pressure levels. A playback system does not include microphones; it simply plays prerecorded material.

plenum space    The plenum space is also called environmental air space. It is an area connected to air ducts that forms part of the air distribution system.

point source    A sound system that has a central location for the loudspeakers, mounted high above, intended to cover a large area. This type of sound system is typically used in a performance venue or a large house of worship.

point-to-point    Conferencing where two sites are directly linked.

polar pattern    Also known as pickup pattern, the shape of the area that a microphone will be most sensitive to sound.

polar plot    A polar plot is a graphical representation of the relationship between a device’s directionality and its output.

port    In a TCP/IP network, a 16-bit number included in the TCP or UDP Transport layer header. The port number typically indicates the Application layer protocol that generated a data packet. A port may also be called by its associated service (e.g., port 80 may be called HTTP, or port 23 may be called telnet).

Port Address Translation (PAT)    A method of Network Address Translation (NAT) whereby devices with private, unregistered IP addresses can access the Internet through a device with a registered IP address. Unregistered clients send datagrams to a NAT server with a globally routable address (typically a firewall). The NAT server forwards the data to its destination and relays responses to the original client.

post tension type construction    A type of structure that uses metal cables embedded within the concrete slab to support the structure. The cables act as a suspension support system that allows for wider spacing of columns within a building.

potential acoustic gain (PAG)    The potential gain that can be delivered by the sound system without ringing and before feedback occurs. It is based upon the number of open microphones and the distances between sources (like a presenter) and microphones, microphones and loudspeakers, and listeners and loudspeakers.

power    Energy expended in one form manifesting itself into another form: motion, heat, or light. This is power, or the rate at which work is done. It is represented by the letter P and is measured in watts (W).

power amplifier    Boosts the audio signal enough to move the loudspeakers.

power conditioners    Enhance the quality of power going to equipment by regulating voltage, eliminating noise or correcting other issues.

power distribution unit (PDU)    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 sequencing    The act of powering on and off equipment that often requires warm-up or cool-down time. Sequencing also helps prevent tripping circuit breakers by limiting the excessive surge of electricity when devices are first turned on.

preamplifier    Boosts the electronic signal captured by the microphone before it is sent to other equipment.

primary optic    The lens that focuses the image onto the screen.

program report    A document that describes the client’s specific needs, system purpose and functionality, and the designer’s best estimate of probable cost, in a nontechnical format for review and approval by the owner. This is also known as the AV narrative, or discovery phase report, return brief, or concept design report.

progressive scanning    Scanning that traces the image’s scan lines sequentially, such as with an analog computer monitor.

Protocol Independent Multicast (PIM)    Allows multicast routing over LANs, WANs, or even, theoretically, the open Internet. Rather than routing information on their own, PIM protocols use the routing information supplied by whatever routing protocol the network is already using; that’s why it’s protocol independent.

pulling tension    The maximum amount of tension that can be applied to a cable or conductor before it is damaged.

pure tone    See fundamental frequency.

Q factor    The ratio of the height of the peak of the filter against the width of the filter at the 3 dB point.

quality of service (QoS)    Any method of managing data traffic to preserve system usefulness and provide the best possible user experience. Typically, QoS refers to some combination of bandwidth allocation and data prioritization.

quiet ground    A point on a ground system that does not inject spurious voltages into the computer system. There are no standards to measure how quiet a quiet ground is.

raceway    An enclosed channel of metal or nonmetallic materials designed for holding wires, cables, or busbars, with additional functions.

rack    See equipment rack.

rack elevation diagram    A rack elevation diagram is a pictorial representation of the front of a rack and the location of each piece of equipment within that rack, typically labeling the number of RUs used for each piece of gear.

rack unit (RU)    A unit of measure of the vertical space in a rack. One RU equals 1.75 inches (44.5 mm).

radio frequency (RF)    The portion of the electromagnetic spectrum that is suitable for radio communications. Generally, this is considered to be from 10 kHz up to 300 MHz. This range extends to 300 GHz if the microwave portion of the spectrum is included.

radio frequency interference (RFI)    Radiated electromagnetic energy that interferes with or disturbs an electrical circuit.

rarefaction    A decrease of density and pressure in air molecules.

ratio    A mathematical expression that represents the relationship between the quantities of numbers of the same kind. A ratio is typically written as X:Y or X/Y.

RCA connector    Also known as a phono connector, a connector most often used with line-level audio signals.

reactance (X)    Opposition to alternating current resulting from capacitance and inductance in the circuit.

rear-screen projection    A system in which the image is projected toward the audience through a translucent screen material, for viewing from the opposite side.

reference level    In the context of decibel measurements, the reference level is the established starting point represented by 0 dB. The reference level varies according to linear unit and application.

reference point    The point of no potential used as the 0 V (zero volt) reference for a circuit.

reflected ceiling plan    Used to illustrate elements in the ceiling with respect to the floor. It should be interpreted as though the floor is a mirrored surface, reflecting the features within the ceiling.

reflecting server    Takes in a unicast stream and broadcasts out a multicast stream. It is often used for live data streams.

reflection    Light or sound energy that has been redirected by a surface.

reflective technology    Any display device that reflects light to create an image.

refraction    The bending or changing of the direction of a light ray when passing through a material, such as water or glass. How much light refracts, meaning how great the angle of refraction, is called the refractive index.

refresh rate    The number of times per second a display, such as a monitor, television, or projector, will draw the image sent to it.

release time    The release time of an audio compressor determines how quickly the volume increases when an audio signal returns below the threshold.

relocatable power tap    A cord-connected product rated 250 V AC or less and 20 A or less with multiple receptacles. This tap is intended only for indoor use and plugged directly into a branch circuit. It is not intended to be connected to another relocatable power tap.

reserve DHCP    A hybrid approach to IP addressing. Using reserve DHCP, a block of statically configured addresses can be set aside for devices whose IP addresses must always remain the same. The remaining addresses in the subnet will be assigned dynamically. The total pool of dynamic addresses is reduced by the number of reserved addresses.

resistance    The property of a material to impede the flow of electrical current, expressed in ohms.

resistor    A passive electrical component that produces equal impedance to current flow. Current passes through a resistor in direct proportion to voltage, independent of frequency, as outlined in Ohm’s law.

resolution    1. The amount of detail in an image. 2. The number of picture elements (pixels) in a display.

reverberant sound    Sound waves that bounce off multiple surfaces before reaching the listener but arrive at the listeners’ ears quite a bit later than early reflected sound.

reverberation    Numerous, persistent reflections of sound energy.

RF    See radio frequency (RF).

RF control    RF control is generally employed as a user interface to the control system. Some manufacturers’ devices provide control links into their components using RF transmission, as this affords the ability to control devices when line of sight is not possible.

RF system    A closed-circuit system with the composite video and audio signals modulated at a certain frequency, called a channel. RF systems require a display device (such as a television) with a tuner set to a selected channel to display the information modulated onto that frequency.

RGBHV signal    A high-bandwidth video signal with separate conductors for the red signal, green signal, blue signal, horizontal sync, and vertical sync.

RGBS signal    A four-component signal composed of a red signal, a green signal, a blue signal, and a composite sync signal.

RGsB signal    A three-component signal composed of a red signal, a green signal with composite sync added to the green channel, and a blue signal. It is often called sync on green.

rigid metal conduit    Rigid metal conduit, called rigid, is the heaviest conduit and offers the best physical and EMI protection.

rigid nonmetallic tubing    Rigid nonmetallic tubing is very stiff with a thick wall but lightweight. It is similar to plumbing tubing. Because it is not flexible, it is available in preformed pieces at various angles.

ring    A network topology that connects terminals, computers, or nodes in a continuous loop.

room criteria (RC) rating    With measurements taken at eight center-octave frequencies from 31.5 to 8,000 Hz, the average of the measurements taken from 500, 1,000, and 2,000 Hz. This includes additional steps to rate the background noise as (N) for neutral, (R) for rumbly, or (H) for hissy.

room mode    Also called a standing wave; occurs between parallel surfaces of an enclosure (could be a room, a loudspeaker cabinet, and so on) where the dimension between those parallel surfaces equals one-half wavelength (and the harmonics thereof). The wave is thus reflected on itself out of polarity, creating location-specific areas of maximum and minimum pressure.

router    A device that works on the OSI layer above the Network and Transport layers. A router knows the IP address of sent packets, and it can send them to specific locations on the network. The IT manager can use a router to change how the network works and allows for redundancy in the network.

RS-232    The interface between data terminal equipment and data circuit-terminating equipment employing serial binary data interchange. It supports a single-ended mode of operation with one driver and one receiver. It supports a maximum cable length of 50 feet (15 m) with a data rate of 20 kbps.

RS-422    Provides the electrical characteristics of balanced voltage digital interface circuits. It is a balanced signal with one driver and 10 receivers with multidrop capability. The maximum cable length for RS-422 is 4,000 feet (1,220 m) with a data rate of 10 Mbps.

RS-485    RS-485 supports a differential mode of operation with 32 drivers and 32 receivers and multidrop capability. The maximum cable length for RS-485 is 4,000 feet (1,220 m) with a data rate of 10 Mbps.

RsGsBs    Red, green, and blue signals with composite sync added to each color channel. This requires three cables to carry the entire signal. It is often referred to as RGB sync on all three.

RT₆₀    The time taken for the energy in an initially steady reverberant sound field to decay by 60 dB after the source of the sound ceases.

RU    See rack unit (RU).

sampling rate     The number of samples taken per unit of time (typically seconds) when converting a continuous (analog) signal to a discrete signal (typically a digital signal).

scale    One number being equivalent to another number in a ratio, for example, 1/4 inch = one foot.

scaler    A feature in a display device that changes the size of an image without changing its shape. Scaling may be required when the image size does not fit the display device.

scan rate    The frequency of occurrence of a display drawing one line of information.

scattering    When light hits a textured surface, the incoming light waves get reflected in multiple angles because the surface is uneven.

scene    A recallable preset of lighting levels for one or more zones.

scope statement    A written agreement between the client, the project sponsor, the key stakeholders, and the project team that defines the boundaries of the project.

screen gain    Describes the distribution of light reflected off a projection screen. The amount of gain is compared to a matte-white screen, which reradiates light and distributes it with perfect uniformity.

SDTV    Standard-definition television.

section drawing    A section drawing is a view of the interior of a building in the vertical plane. Section drawings show a bisected wall, which allows you to view what is behind it.

sensitivity specification    A way to determine a device’s ability to convert one form of energy into another form of energy. It is used to define the device’s efficiency in converting from one form to another.

serial digital interface (SDI)    An uncompressed, unencrypted, standardized digital video signal.

series circuit    When all the current supplied by the source will flow through the entire circuit. The electrons leaving the source of power go through each component of the circuit and return to the source. While all the current flows through all the circuit, the voltage is divided between the three resistors (loads) as well as the wire that connects them.

series/parallel loudspeaker circuit    When groups of loudspeakers called branches are wired together in series. Typically, loudspeakers in the same branch have the same impedance. Each branch is connected to the positive and negative lines of the amplifier in parallel.

server    A powerful computer, typically with large amounts of storage and more memory, computing capacity, and redundancy than a desktop computer.

service level agreement (SLA)    Used to document agreements between an IT service provider and a customer. It describes the services to be provided; documents service-level targets; and specifies the roles and responsibilities of the service provider(s) and the customer(s).

shear    The tendency of a mount to tear or cut off from the structure.

shield    A metallic partition placed between two regions of space. A shield is used to control the propagation of electric and magnetic fields from one of the regions to the other. It contains electric and magnetic fields at the source or to protect the receiver from electric and magnetic fields. A shield can be the chassis (metallic box) that houses an electronic device or the metallic enclosure (aluminum foil or copper braid) that surrounds a wire or cable.

shotgun microphone    A long, cylindrical, highly sensitive, unidirectional microphone used to pick up sound from a great distance.

sightline    The unobstructed view between a person and the object he needs to see. A sightline study determines the most appropriate seating layout for a clear field of view, including the lowest visible point on the display wall, nearest viewers’ line of sight, farthest viewers’ line of sight, distortion of image from off-axis seat locations, and other ergonomic factors for a preferred field of vision and viewing comfort tolerances.

signal flow    The traceable path of signals through a system.

signal generator    A test equipment instrument that produces calibrated electronic signals intended for the testing or alignment of electronic circuits or systems.

signal ground    1. A 0 V (zero volt) point of no potential that serves as the circuit reference. 2. A low-impedance path for the current to return to the source.

single-phase power    Alternating current electrical power supplied by two current-carrying conductors. This type of power is used for residential and some light-commercial applications.

single-point ground (SPG)    In the context of IEEE Std. 1100, refers to implementation of an isolated equipment grounding configuration for the purposes of minimizing problems caused by circulating current in ground loops.

signal-to-noise (S/N) ratio    The ratio, measured in decibels, between the audio or video signal, and the noise accompanying the signal. The higher this ratio, the better the quality of the sound or picture.

Simple Network Management Protocol (SNMP)    A set of Internet Engineering Task Force (IETF) standards for network management, including an Application layer protocol, a database schema, and a set of data objects. SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be queried, and sometimes set, by managing applications.

socket    In a TCP/IP network, the combined port number, Transport Layer protocol identifier, and IP addresses of communicating end systems. A socket uniquely identifies a session of a given transport protocol.

sound pressure level (SPL)    In the context of Standard 1M, all sound pressure levels are expressed in unweighted decibels.

sound reinforcement system    The combination of microphones, audio mixers, signal processors, power amplifiers, and loudspeakers that are used to electronically amplify and distribute sound.

source-specific multicast (SSM)    In streaming, allows clients to specify the sources from which they will accept content. This has the dual benefit of reducing demands on the network while also improving network security. Any device that has the host address can try to send traffic to the multicast group, but only content from the specified source will be forwarded to the group.

specification    A written, precise description of the design criteria for a piece of work. Specifications define the level of qualitative and/or quantitative parameters to be met and the criteria for their acceptance. All specifications must be formulated in terms that are specific, measurable, and verifiable and unambiguous.

specular reflection    A mirrorlike reflection of energy, in which most of the energy is reflected back in a single direction.

speech privacy system    A sound system that adds background noise to an environment to cover up human speech and prevent privacy issues.

speech-reinforcement system    An audio system that reinforces or amplifies a presenter’s voice to be heard over a larger audience.

splitter    An electronic device that divides a signal into different pieces to route to different devices.

spot photometer    A type of meter used to measure luminance.

standing wave    Occurs between parallel surfaces of an enclosure (could be a room, a loudspeaker cabinet, and so on) where the dimension between those parallel surfaces equals one-half wavelength (and the harmonics thereof). The wave is thus reflected on itself out of polarity, creating location-specific areas of maximum and minimum pressure.

star topology    A network topology where all network devices are connected to a central network device, usually a hub or a switch.

static IP address    A manually assigned permanent IP address.

stereophonic    Commonly shortened to stereo, describes when input from all microphones is split into at least two channels before driving the signal through the loudspeakers.

streaming video/streaming audio    Sequence of moving images or sounds sent in a continuous, compressed stream over the Internet and displayed by the viewer as they arrive. With streaming video or audio, a web user does not need to wait to download a large file before seeing the video or hearing the sound.

subnet    A logical group of hosts within a local area network (LAN). A LAN may consist of a single subnet, or it may be divided into several subnets. Additional subnets may be created by modifying the subnet mask on the network devices and hosts.

subnet mask    A binary number whose bits correspond to IP addresses on a network. Bits equal to 1 in a subnet mask indicate that the corresponding bits in the IP address identify the network. Bits equal to 0 in a subnet mask indicate that the corresponding bits in the IP address identify the host. IP addresses with the same network identifier bits as identified by the subnet mask are on the same subnet.

subwoofer    A loudspeaker that reproduces lower frequencies, typically 20 Hz to 200 Hz.

supercardioid polar pattern    The exaggerated heart shape of the area that a highly directional microphone is most sensitive to sound.

surface-mount microphone    Also called a boundary microphone, a microphone placed on a table to pick up sound. This type of microphone is often used in boardrooms and other environments where a number of talkers must be picked up and the microphone needs to remain unobtrusive.

surround-sound system    A stereo playback system that uses from two to five channels for realistic sound production, producing an experience where the sound appears to surround listeners. This is best achieved using surround-encoded material, a receiver, and surround loudspeakers.

S-Video    A video signal, also known as Y/C. Y is the luminance, and C is the chrominance. Y and C are transmitted on separate conductors.

switcher    A peripheral or sometimes integrated device used to select one of a group of signals.

sync    Synchronization. The timing information that keeps images displaying properly.

system    In the AV industry, a compilation of multiple individual AV components and subsystems interconnected to achieve a communication goal.

system black    The lowest level of luminance a system is capable of producing for its task operating conditions. The system includes projector, screen, the light the projector produces, and ambient light.

system grounding    The intentional grounding of one of the current-carrying conductors in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines, and that will stabilize that voltage to earth during normal operation.

tap    A connection to a transformer winding that allows you to select a different power level from the transformer.

task lighting    Lighting directed to a specific surface or area that provides illumination for visual tasks.

tensile strength    The maximum force that a material can withstand before deforming or stretching.

three-phase power    Alternating current electrical power supplied by three current-carrying conductors, each offset by 120 degrees from one another. A fourth conductor, a neutral, is used as the return conductor. This type of power is used for commercial and industrial applications.

threshold    The level at which the desired function becomes active. Generally speaking, a lower threshold level means it will activate earlier. Recommended starting threshold for most line-level (post-preamp) functions is 0 dBu.

throw distance     The distance from a projector to a focusing surface or the screen.

Thunderbolt    Interface technology developed by Intel that transfers audio, video, power, and data over one cable in two directions. Thunderbolt versions 1 and 2 use the same connector as Mini DisplayPort (MDP), while Thunderbolt 3 uses USB Type-C.

time code    A method of numbering video frames according to the Society of Motion Picture and Television Engineers (SMPTE) standards. The code is the eight-digit address representing the hour, minute, second, and frame recorded on the videotape’s control track.

time domain     A view of a signal as amplitude versus time, which allows you to see the amount of acoustical energy present over a period of time.

Time-Sensitive Networking (TSN)    In 2012, the IEEE working group overseeing the Audio Video Bridging standard was renamed Time-Sensitive Networking to reflect the standard’s applicability to communication among different types of devices, such as network sensors. See Audio Video Bridging (AVB).

transduction    The process by which one type of energy changes to another.

transformer    A passive electromagnetic device commonly consisting of at least two coils of wire (inductors) with no physical connection between them. Most often, these coils share an iron-based alloy core. This common core aids in concentrating the magnetic lines of force created by the current flow in one coil (primary), thereby inducing a voltage into the other coil (secondary).

transient disturbance    A momentary variation in power, such as a surge, spike, sag, blackout, or noise.

transition-minimized differential signaling (TMDS)    A technology for transmitting graphics to a display at high speeds. It supports high resolutions, such as 9.2 megapixel (3840×2400) displays, and native 16 million true-color resolutions.

transmission    Passing of sound energy through partitions or structure-borne vibrations.

Transmission Control Protocol (TCP)    A connection-oriented, reliable Transport layer protocol. TCP transport uses two-way communication to provide guaranteed delivery of information to a remote host. It is connection-oriented, meaning it creates and verifies a connection with the remote host before sending it any data. It is reliable because it tracks each packet and ensures that it arrives intact. TCP is the most common transport protocol for sending data across the Internet.

transmission loss    Attenuation that occurs when sound goes through a barrier or partition, expressed in decibels, and is affected by the barrier or partition’s mass, stiffness, and damping.

transmissive technology    Any display device that creates images by allowing or preventing light to pass.

tweeter    A loudspeaker that is designed to reproduce frequencies above 3000 Hz.

twisted-pair    Any number of wires that are paired together and twisted around each other. The wires can be shielded or unshielded.

Ultra HD    A term used to describe video formats with a minimum resolution of 3840×2160 pixels in a 16×9 aspect ratio.

unbalanced circuit    A two-conductor circuit in which one conductor carries the signal and the other conductor carries the return. The return conductor is usually the cable shield and is a low-impedance connection, as it is connected to the signal ground and possibly also to the earth ground. The impedance of the signal circuitry is quite different from the return circuitry, which is why the impedances of the two conductors are quite different—the impedances are unbalanced with respect to one another.

unicast streaming    Unicast streaming is a one-to-one connection between the streaming server sending out the AV data and client devices listening to the stream. Each client has a direct relationship with the server. The client sends a request to the server, and the server sends the client a stream in response. Since the server is sending out a separate stream for each client, each additional client takes up more bandwidth. Streaming media to three clients at 100 Kbps actually uses 300 Kbps of bandwidth. IP Unicast streams may use either UDP or TCP transport, although with TCP transport, there will always be some buffering.

unity gain    Derived from the number 1, refers to no change in gain.

Universal Serial Bus (USB)    An industry standard for connecting, communicating, and supplying power between computers and electronic devices. Version 3.1 of USB is capable of 10 Gbps—enough to transmit 4K video. USB 3.1 can utilize a USB Type-C (USB-C) connector, which supports DisplayPort, HDMI, power, all USB generations, and VGA.

unshielded twisted-pair (UTP) cable    Typically used for data transfer, UTP cable contains multiple two-conductor pairs twisted at regular intervals, employing no external shielding.

vectorscope    A vectorscope is a specialized oscilloscope used in video systems to measure chrominance accuracy and levels.

vertical scan rate    The vertical scan rate describes the number of complete fields a device draws in a second. This may also be called the frame rate, vertical sync rate, or refresh rate. The vertical scan rate is measured in hertz (Hz) or cycles per second.

video wall    A video wall features several monitors, video screens, display cubes, video projectors, or TV sets that are set up on top of each other or side by side to form a single, large contiguous display.

viewing angle    Determines how far off-axis (screen centerline) a viewer can sit and still see a good-quality image. This is no greater than 45 degrees off the projection axis.

viewing area plan    A plan-view drawing of the viewing environment that identifies five viewing locations as defined in the requirements section of the ANSI/INFOCOMM 3M-2011 Standard.

viewing cone    The best viewing area for the audience. The term cone is used because there is width, height, and depth to the best viewing area, and this area emanates from the center of the screen.

virtual local area network (VLAN)    Connects separate LANs to form a logical group. For instance, the LANs at each branch of a large company could be combined into one company-wide VLAN.

virtual private network (VPN)    Uses the Internet to create a tunnel between two or more local area networks (LANs). VPNs are used to create virtual wide area networks (WANs) and for remote monitoring, troubleshooting, and control. VPNs are typically controlled and configured by the enterprise network administrator. Each host requires the proper software, access rights, and password to log into the client network.

visual field    The point of space that can be seen when a person’s head and eyes are absolutely still. It is measured in angular magnitude, or degrees. The visual field of a single eye is termed monocular vision, and the visual field where the perceived image from both eyes overlap is called binocular vision.

Voice over Internet Protocol (VoIP)    Allows the digital transmission of phone calls and multimedia over the Internet and other networks. VoIP is relayed over smartphones and other Internet devices and requires equipment such as VoIP routers, phone adapters, telephone sets, and more.

volt (V)    The basic international unit of potential difference or electromotive force.

voltage    The electrical potential to create current flow in a circuit.

watt    The measurement of the amount of power consumed by a system. It is represented in math by the symbols P or w.

waveform monitor    A specialized oscilloscope used to display and analyze the video signals sync, luminance, and chroma levels.

wavelength    The distance between two corresponding points of two consecutive cycles measured in meters.

wayfinding    The use of visual guides or signage in strategic locations to help travelers more easily navigate to a destination.

webcasting    Allows the broadcast of digital media such as audio or video over the Internet, which audience members can stream live or access on demand. Essential equipment for webcasting includes computers, streaming servers, production software, recording gear, appliances, and more.

white noise    A sound that has the same energy level at all frequencies.

wide area network (WAN)    A data communications system that uses telecommunication circuits to link local area networks (LANs) that are distributed over large geographic distances. A wide area network (WAN) covers a large geographical area, such as a state or country. The Internet, which covers the entire world, is one large WAN.

wire    A single conductive element intended to carry a voltage or electronic signals.

wireless local area network (WLAN)    A network that shares information by radio frequency (RF).

woofer    A loudspeaker that has low frequencies, typically 20 Hz to 200 Hz.

work breakdown structure (WBS)    A deliverable-oriented grouping of project elements that will ultimately organize and define the total scope of the project. Each descending level represents an increasingly detailed definition of a project component.

XLR connector    A popular type of audio connector featuring three leads: two for the signal and one for overall system grounding. This is a secure connector often found on high-quality audio and video equipment. It is sometimes called a cannon connector.

Y/C    A video signal, also known as S-Video. Y is the luminance, and C is the chrominance. Y and C are transmitted on separate synchronized conductors.

zone    In the context of lighting, a zone is a grouping of luminaires (lighting fixtures) that are controlled together. In the context of digital signage, a zone is an area where separate content may be placed. A different playlist must be created for each zone.