AV/IT Glossary—27 Days of #AVabc—B

Bonjour—Bonjour is Apple's version of the Zero Configuration Networking (Zeroconf) standard, a set of protocols that allows certain communication between network-connected devices, applications and services. Bonjour is often used in home networks to allow Windows and Apple devices to share printers.


Back Porch—The time in a composite video signal that is between the trailing edge of the sync pulse and the trailing edge of the blanking pulse (before the video information). Also see "Blanking."

Backbone—The primary transmission network for telecommunications that connects between key locations and branches off to buildings and other facilities.

Backreflection—Light within an optical fiber that is reflected back toward the source. This typically occurs at interfaces between the fiber and the connector where an air gap causes the reflection.

Baffle—The front surface of a loudspeaker, on which the drivers are mounted.

Backscattering—The portion of light within an optical fiber that is scattered back toward the source.

Balanced Audio—The audio signal that is carried on three wires (or five wires for stereo pair), with two of them carrying the same signal but with reversed polarity, and a third wire for shielding. Since the two signal wires would pick up virtually identical noise from outside (common mode noise), and that noise can be canceled out at the receiving end by a differential amplifier, the balanced audio is much less susceptible to hum and interference from long cable runs.

Balanced Cable—A cable that carries a balanced signal on three conductors. Contrast with unbalanced (or “single-ended”) cable.

Balanced Circuit—A circuit in which two branches are electrically alike and symmetrical with respect to a common reference point, usually ground; preferred to an unbalanced circuit due to its ability to reject noise.

Balanced Output—A connector on some A/V products that presents the audio signal on three conductors, rather than the two conductors of an unbalanced output. Balanced outputs appear on XLR jacks. Found only on high-end products.

Balanced Signal—A signal that is divided into two antiphase signals, traveling on two wires (and sometimes with a third - a ground reference wire). Transmitting a balanced signal achieves better signal to noise ratio, and the signal is more immune to noise and interference. The receiving end requires a differential amplifier, which amplifies only the differences between the antiphase signals, thus canceling noise picked up on the way. The balanced system is used either when very low signals are to be transmitted over long distances (such as those generated from high quality microphones) or at broadcast audio studios for highest quality signal recreation. The balanced signal system is used in TP* (Twisted Pair) wire setups when it is essential to use non-coaxial wires for data, video, audio or graphics transmissions.

Banana Jack—A small tubular connector found on A/V receivers and power amplifiers for connecting speaker cables terminated with banana plugs.

Banana Plug—A common speakercable termination that fits into a banana jack.

Bands—A grouping or range of frequencies.

Band Pass Filter—A filter that allows a specific range to pass. The bandpass frequencies are normally associated with frequencies that define the half power points, i.e. the -3 dB points. In multi-driver speaker systems, for example, the mid-range driver may be fed by a bandpass filter.

Band Reject Filter—A filter that combines the characteristics of a low pass and a high pass filter that is used to block a narrow band of frequencies, while allowing frequencies above or below this band to pass. (i.e. notch filter)

Banding—A video problem of dark bars appearing across the displayed image in areas where there is movement.

Bandwidth—The total range of frequencies required to pass a specific signal without significant distortion or loss of data. In analog terms, the lower and upper frequency limits are defined as the half power, or -3 dB signal strength drop, compared to the signal strength of the middle frequency, or the maximum signal strength of any frequency, expressed as xx Hz to xx kHz (or MHz) @ -3 dB. In digital terms, it is the maximum bit rate at a specified error rate, expressed in bits per second (bps). A device's bandwidth should be wider than the highest possible bandwidth of the signals it may handle. (In general, the wider the bandwidth, the better the performance. However, bandwidth that is too wide may pass excessive noise with the signal.)

Bandwidth Compression—A process that reduces digital signal bandwidth in order to allow its transmission as a DTV* signal. A 6 MHz transmission bandwidth requires signal bandwidth compression down to about 20 Mbits/sec.

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

Barrel Connector—An adapter used to connect two coax-type connectors of the same gender.

Baseband—A prime signal such as composite video, component video, and audio with its own path but is not modulated onto a carrier signal or combined with other signals on a path. An unmodulated signal or band of signals. The video signal seen on a waveform monitor is a baseband video signal.

Baseband Video—Normally refers to a non-modulated composite video signal, with the frequency spectrum extending from a few Hertz (or from DC) up to several MHz, and covering the full bandwidth of the video signal.

Bass—Sounds in the low audio range, generally 20Hz–200Hz. bass extension The lowest frequency an audio system can reproduce. A measure of how deeply an audio system or loudspeaker will reproduce bass. For example, a small subwoofer may have bass extension to 40Hz. A large subwoofer may have bass extension to 16Hz.

Bass Management—A combination of controls and circuits in an A/V receiver or controller that determines how bass frequencies are distributed among the loudspeakers.

Bass Reflex—A speaker with a hole or slot in the cabinet that allows sound inside the cabinet to emerge into the listening room.

Baud—Named for J. M. E. Baudot, the inventor of the Baudot telegraph code. The number of electrical oscillations per second, called baud rate. Related to, but not the same as, transfer rate in bits per second (bps).

Below Black—Below black Information in a video signal that falls below the technical threshold of black, 7.5 IRE. Some DVD players pass signals that are below black; others do not.

Bend Loss—In fiber optics, the attenuation of light as it passes through a fiber with excessive bending. Macrobending and microbending both contribute to bend loss.

Bend Radius—The smallest radius at which an optical fiber or fiber optic cable can be bent without introducing attenuation or damage to the fiber.

Bending—A video problem when the top of the screen hooks, bends, or tears to the side. Also known as “hooking.”

BER-Bit Error Rate—The rate at which bit errors are experienced across a data connection.

Best Effort—Describes a network service in which the network does not provide any guarantees that data is delivered or that a user is given a guaranteed quality of service level or a certain priority.

Beta(max)—A video recording and playback* standard on 1/2" tapes distributed mainly by Sony™. From its inception BETAMAX competed with the VHS* system developed by JVC™. Both were intended for home use and there was no substantial difference between the two formats. Today, the Betamax system for home video is practically non-existent as that market is completely dominated by the VHS system.

Betacam—BETACAM and BETACAM SP are wide-spread professional video recording and playback formats. BETACAM uses 1/2 inch tapes, employing the component video* system for highest professional quality outputs. Many editing systems* and controllers are designed around this format.

Betacam-sx—A digital video format introduced by SONY™. This format uses MPEG* compression with a data rate of 18Mbits/sec. The compression ratio is high - approaching 10:1. Output quality is very good despite the high compression ratio because it uses an MPEG-2 4:2:2 profile. Cassettes use metal particle technology and come in two sizes - 60 minutes for fieldwork and 184 minutes for studios. These VCRs also play analog Beta tapes, for backward compatibility.

Bezel—Bezel is a term used to describe the outside frame of a computer, monitor or any other computing device. This is important for product developers and designers in evaluating the overall perimeter of the device/component and its possible ramifications. Newer device designs such the iPad have extremely narrow bezels, allowing for more screen. This has become an increasingly important design factor for consumers.

B-Frame—Bi-directionally predictive coded picture. Contains predictive, difference information from the preceding and following I- or P-frame within a GOP. Data preceeding or following the B-frame are required to recreate video information in a B-frame.

Bi-Amp/bi-amping—Using two power amplifiers to drive one loudspeaker. One amplifier typically drives the woofer, while the second drives the midrange and tweeter.

Bidirectional—The ability to move, transfer or transmit in both directions.

Bi-Directional 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.

Big Screen—A large-screen directview television or rear-projection set. Usually reserved for sets with diagonal dimensions greater than 40 inches.

Binary—A numbering system using base-2. Each digit is represented by a 1 or a 0 (on or off).

Binary Code—A coding system using the digits 0 and 1 to represent a letter, numeral, or other character in a computer. For example: the character “A” in ASCII code becomes 0100 0001 in binary.

Binding Post—A connection on receivers and power amplifier for attaching loudspeaker cables.

Bipolar Speaker—A speaker that produces sound equally from the front and the back. Unlike the dipolar speaker, the bipolar’s front and rear sound waves are in phase with each other.

B-ISDN-Broadband Integrated Services Digital Network—A special version of ISDN that uses fiber optics and can transfer at 1.5 megabits per second. Also see "ISDN."

Bit—The shortened form of “binary digit” (0 or 1). A bit is the smallest unit of information in a computer.

Bit Depth—The number of bits per pixel. Bit depth determines the number of shades of gray or variations of color that can be displayed by a computer monitor. For example, a monitor with a bit depth of 1 can display only black and white; a monitor with a bit depth of 16 can display 65,536 different colors; a monitor with a bit depth of 24 can display 16,777,216 colors

Bit Error—Bit error indicates the number of bits of a data stream over a communication channel that have been altered. A bit error can result in unusable data or the corruption of an image in video streaming solutions.

Bit Error Rate-BER—The fraction of bits that were transmitted with errors, expressed at the ratio of incorrectly to correctly transmitted bits. BER is used to assess transmission accuracy in a fiber optic system.

Bit Map—A method of graphic display using rows and columns of dots, or pixels. Each pixel location corresponds to a specific location in memory.

Bit Rate—The number of bits that are conveyed or processed per unit of time. The bit rate is quantified using the bits per second (bit/s or bps) unit, often in conjunction with an SI prefix such as kilo- (kbit/s or kbps), mega- (Mbit/s or Mbps), giga- (Gbit/s or Gbps).

Bi-Wire—Connecting a loudspeaker to a receiver or power amplifier with two runs of cable to each of the positive and negative terminals. Possible only with speakers featuring two pairs of input terminals. Bi-wiring results in better sound than single-wiring.

Black—The darkest visible surface created by the absorption of all incident light and color. In video, the absence of picture information.

Black Drop—The black masking area above and below a screen used with a front-projection system.

Black and White—Monochrome (one color) or luma information. In the color television system, the black and white portion of the picture has to be one color: gray, D6500 or 6500° K, as defined by x and y values in the 1939 CIE color coordinate system. Commonly referred to as “D65.”

Black Level—More commonly referred to as “brightness,” the black level is the level of light produced on a video screen. The level of a picture signal corresponding to the maximum limit of black peaks. The bottom portion of the video wave form, which contains the sync, blanking, and control signals. The black level is set by the brightness control.

Blackburst—The video waveform without the video elements. It includes the vertical sync, horizontal sync, and the chroma burst information. Blackburst is used to synchronize video equipment to align the video output. One signal is normally used to set up an entire video system or facility. Sometimes it is called House sync.

Blackburst Generator—A special device for calibrating video equipment by generating a composite video signal with a totally black picture. This blackburst signal is used to synchronize video equipment to provide vertical interval switching. It also provides black level and chroma burst information for maintaining uniform video levels and color information.

Blacker Than Black—Designation of a video signal, part of which (spikes or the sync tip) goes below black level transition. Usually, such signals (besides the sync), are undesirable within the video signal. They appear, however, due to image enhancement or poor transition response of the video amplifier or processor. If the signal excursions below black level are small, they can be ignored. If they are too large, approaching sync tip level, image instability might occur, as the blacker than black spikes may be interpreted as sync pulses. Sometimes those excursions are deliberately created for image enhancement and special effects and copy protection purposes. Digital processing can handle some blacker than black signals.

Black Level Clamping—An electronic process which establishes a fixed DC level for a picture signal at the beginning of each scanning line. The black level* of a video signal is set to a specific, predefined DC voltage. This process is used, for example, when two video signals are to be mixed and the black levels must therefore be equal.

Blanking—The interval after the electron beam completes a scan line and returns (retraces) to the left. During this time, the beam must be turned off (horizontal blanking). Similarly, when the last line has been scanned at the bottom of the screen, the beam must return to the upper left (vertical blanking).

Blanking Adjustment—The ability to adjust the degree of blanking on the image. This is useful for eliminating artifacts such, as closed caption noise or improperly adjusted VTR head-switching that can be seen at the top or bottom of a displayed image.

Blanking Level—The level of a video signal that separates the picture information from the sync information. The level of the front and back porches is 0 IRE units. To blank the video signal, the video level is brought down to the blanking level so nothing is visibly displayed, while the electron beam returns (retraces) to the start of the next line.

Blanking Retrace Period—The period when the screen is darkened, which occurs when the electron ray in a monitor or a TV set retraces to start a new line or a new field. The instantaneous amplitude of that signal is such that it makes the return trace invisible. The blanking period is used to eliminate the appearance of the CRT retrace beam so it will not be visible on the monitor. Switching done during the retrace period results in "clean switching". (See Vertical Interval Switching.)

Blocking—Pieces of wood that have been inserted between structural building elements to provide a secure mounting point for finish materials or products.

Block Diagram—An illustration of the signal path through a given system.

Blooming—Most noticeable at the edges of images on a CRT, blooming is when the beam hitting the screen is too intense and overdrives the phosphors. The edges of an image seem to exceed its boundaries. Thin lines and sharp edges may look thick and fuzzy. This may be caused by the contrast being set too high, or by a high voltage problem.

Blu-ray Disc—New optical disc format that can store 50GB on a duallayer disc the size of a DVD. Competing with HD DVD to be the high-definition replacement for DVD.

Blue Key—Blue key generation is a process, which inserts of one video picture into a predetermined area in another one, through the use of special hardware. The primary picture is shot with the subject against a special blue tinted background. The blue content of this signal is then removed and the second picture is inserted in that area where the blue background was located. Blue keying is a very important special effect, which is often used in news broadcasting where pictures of the news being discussed are viewed on a screen behind the anchorman. An extension of the Blue Key is the Chroma Key*.

Bluetooth—A technology used for wireless transfer of data over a short distance. The technology uses a 2.4 GHz carrier, and is suitable for short distances up to 10 meters (30 feet). It allows for low speed data transmission, up to 720 Kbps. The technology can be used to transfer control data in a video studio, replacing RS-232 wires, as it can work through walls. It can also be used for access control and short-range user ID.

BME-Basic Module Enclosure—Some large devices, such as the Extron Matrix 3200/6400/12800 Switchers, may be contained in more than one enclosure, yet function as a single device. Each physical box, or enclosure, is called a BME.

BMP—A simple graphics Bit Map format created by Microsoft™ for the Windows™ program. Many graphics programs running under Windows, which support formats from monochrome up to 24-bit color, use the BMP format. The BMP format does not support image file compression, so 24-bit, high-resolution color images occupy a large amount of disk space.

BMS / BAS—Building management system (BMS): The BMS is the central management system responsible for any necessary management, oversight, visualization, configuration, and performance monitoring of the building subsystems. A typical BMS provides ancillary oversight responsibility for a given BAS. However, a BMS does not typically provide operational interaction with a BAS. If a BMS interface becomes offline, the BAS continues to perform its required functionality, reducing the potential for a single point of failure.

Building automation system (BAS)—The facility automated control system comprised of all mechanical system automation, and automatic temperature control, lighting control, and other relevant building controls subsystems as defined. The BAS is responsible for the operational functionality of each system. The BAS may run autonomously from other systems and may not require a central building management system (BMS) to operate. In the event of a loss of communication to a BMS server, the BAS shall continue to operate. The BAS is built upon a single network infrastructure. This infrastructure may include field wiring, control network wiring, routers, bridges, raceways, and interfaces as required connecting all subsystems and devices.

BNC-Bayonet Neill-Concelman—A cable connector used extensively in television and named for its inventors. A cylindrical bayonet connector that operates with a twist-locking motion. To make the connection, align the two curved grooves in the collar of the male connector with the two projections on the outside of the female collar, push, and twist. This allows the connector to lock into place without tools.

Boost-Cut—The Bi-directional control of audio and video signals to permit raising and lowering of signal levels.

Boot/Boot-up/Bootstrap—The initialization process a system goes through after power comes on. It may also occur as part of resetting. To start a new beginning, you “pull yourself up by your bootstraps.”

Border—The boundary between two merged video pictures, such as in blue keying* or wiping*. Bordering is a special effect* which can be used in video processing to alter the border from a sharply defined line to a fuzzy ill-defined blend of the two pictures. The width of the border, its color and its texture are easily changed.

Bottles—Color identification signals in the vertical interval period used in the older SECAM system which look like bottles on the oscilloscope.

Bounce Signal—A special, artificially generated video signal for testing, where the APL* is changed at a low rate, testing the low frequency response of a video device as well as black level clamping*.

Boundary Microphone—A microphone that relies on reflected sound from a surrounding surface.

Bow—The curving of scan lines in the center of the image.

Breakaway—The ability to separate audio and video signals for switching them independently. For example, the audio and video signals from one source may break away and be switched to two different destinations. This is the opposite of the term “audio follow.”

Breakdown Voltage—The voltage level at which the insulation between conductors fails and electricity flows between the conductors.

Breakout Cable—In fiber optics, a cable comprising a bundle of several jacketed fibers, with the fibers separated from the bundle at one end to facilitate installation into panels and other equipment. The fibers are individually jacketed.

Breakout Kit—In fiber optics, a kit used to create a breakout cable from bundled fiber optic cable.

Breezeway—The early part of the back porch portion of the video signal. The area between the horizontal sync pulse and the color burst.

Bridge—A bridge is a type of computer network device that provides interconnection with other bridge networks that use the same protocol. Bridge devices work at the data link layer of the Open System Interconnect (OSI) model, connecting two different networks together and providing communication between them. Bridges are similar to repeaters and hubs in that they broadcast data to every node. However, bridges maintain the media access control (MAC) address table as soon as they discover new segments, so subsequent transmissions are sent to only to the desired recipient. Bridges are also known as Layer 2 switches.

Bridge (or multipoint bridge)—A device that allows multiple systems to dial in and participate in a single videoconference.

Bridging (or Bridged) Audio—Some stereo amplifiers are designed to allow “bridging” or combining the power output of two channels into one channel. Bridging allows the amplifier to drive one speaker with more power than the amp could produce for two speakers. Not all amplifier designs allow bridging, however. NEVER attempt bridging of an amplifier without first consulting the manufacturer’s documentation and instructions.

Brightness—Usually refers to the amount or intensity of video light produced on a screen without regard to color. Sometimes called “black level.”

Brightness Control—The control on a television monitor that increases or decreases the radiance of an image.

Brightness Ratio—The difference between the lightest (whitest) and darkest (blackest) areas in an image. The wider the brightness ratio, the wider the contrast ratio.

Brightness Signal—Same as the luma (Y) signal; a signal that carries information about the light intensity at each point in the image.

Broadband—A communications channel that has greater bandwidth than a voice-grade line and is capable of greater transmission rates.

Broadcast—The operation of sending network traffic from one network node to all other network nodes.

BT.2020—Formally ITU-R Recommendation BT.2020, and also known as Rec. 2020. The international standard for Ultra HD video that specifies the 3840x2160 and 7680x4320 resolutions, color space parameters that define a much wider color gamut than previous specifications, frame rates up to 120 fps, color bit depth up to 36 bits per pixel, digital color encoding, chroma subsampling, and more.

BT.709—Formally ITU-R Recommendation BT.709, and also known as Rec. 709. The international standard for high-definition video that specifies resolutions, frame rates, digital color encoding, color space parameters, and more.

Buffer—1) In electronics, a circuit such as a unity gain amplifier used to isolate the signal source from the load. A buffer can be used for digital or analog signals. 2) In digital systems, a region of memory used to temporarily hold data while it is being delivered from one process to another.

Buffer Amplifier—An electronic device that provides some isolation between other components.

Buffer Coating—A plastic coating applied to an optical fiber that provides protection from moisture or damage, as well as handling during the manufacturing of fiber optic cable.

Buffer Tube—An additional plastic tubing around the buffer coating of an optical fiber that provides added protection. This tubing is typically colored.

Burn-In—In a video or plasma display, this term describes what happens when an image has been displayed too long, a permanent image is burned into the screen phosphor.

Burst—A sequence of data delivered in a short period of time. Network designs must account for both predictable data traffic and bursts of traffic.

Burst Error—Consecutive data errors that occur suddenly. If errors spanning several bytes occur, complete decoding at the receiving end may not be possible even if error correction is applied. As a measure against burst errors, methods such as interleaving are used. Errors occurring on real world networks are typically burst errors.

Burst Gate—The signal generated in many video processors starting at the outset of the color burst signal* and ending at the end of that signal. This burst gate signal is mainly used for black level clamping * and DC restoration.

Bus (or buss)—A path for transporting voltages, signals, or a ground between the different sections of an electronic device, such as a data bus between a CPU and memory or a peripheral device. Its width is determined by the number of lines (conductors) that make up the bus, and its speed (data transfer rate) is determined by the circuits that drive the lines.

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

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