Television and Video Glossary -- A-B
Here is a discussion of common words and phrases used in television and video explained in a way almost everybody can understand. Interesting comments are added to some descriptions.
January 2009. We are re-assembling our web site. Please excuse any broken links.
We regret that we do not have many audio topics described here.
Last updated 10/16/06
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Numbers are treated as if they were spelled out in words, for example "9-Eyes" would be alphabetized as "nine...". Punctuation marks are treated as spaces, for example "R-Y" would be alphabetized with "R" as an initial, preceding words beginning with "R". Acronyms such as "RGB" are alphabetized as words, not initials. Generally acronyms which are proper names or trademarks (such as RIAA, DVI) have the definition alongside while acronyms which are not names (CAV, AM) have the definition alphabetized with the spelled out meaning of the acronym.
A/D -- Analog to Digital.
Aberration -- Imperfections in the focusing characteristics of a lens or lens system. Spherical aberration -- Light rays from the center of the lens would come to a focus at a different distance compared with light rays from the periphery of the lens, making the overall focus less precise. Chromatic aberration -- Light rays of different colors would come to a focus at different distances from a lens (red is "bent" or refracted least), giving a rainbow fringe around objects and also making the overall focus less precise.
AC-3 -- Audio Code 3.
Academy Ratio -- Loosely, the 4:3 aka 1.33:1 aspect ratio (more correctly 1.37:1), which aspect ratio was the standard for shooting movies up until the 1950's.
Acoustic Suspension -- Refers to a speaker intended to be installed in a sealed cabinet, where the air inside helps return the speaker cone to the center position of its excursion. Cabinet design is less critical since it is not necessary to account for the phasing of sound waves from the rear of the speaker cone escaping into the room. Acoustic suspension speaker systems are generally less efficient than other speaker system types since the speaker cone excursion is large and to achieve uniform magnetic field interaction needed for low distortion the speaker usually has a deep voice coil and shallow magnetic field as opposed to the electrically more efficient and more expensive vice versa. In addition sound waves from the rear of the speaker cone do not contribute to the overall sound output.
Active Crossover, Filter, Switcher, etc. -- Electronic circuitry or device that uses transistors or other components and that requires a power source to perform the desired function. A switcher that has remote control capability is always active.
Active Scan Line -- Refers to a scan line holding picture information including black for letterbox bars, as opposed to synchronizing information or encoded closed caption text. On this web page we sometimes say "illuminated scan line" when we mean "active scan line". As an example NTSC video has 525 scan lines of which approximately 480 are active.
Addressable Resolution -- Refers to the number of apparently diferent positions on the screen that can be individually illuminated, although not necessarily distinguished as separate closely spaced picture details. For a CRT it is subjective and theoretically infinite. With few exceptions, for non-CRT displays the addressable resolution equals the pixel count, for example 1280 x 720 pixels, of the display element. (In one exception, Wobulation (tm), the addressable resolution is currently twice the pixel count of the display element.)
AFC -- Automatic Frequency Control.
AFT -- Automatic Fine Tuning.
AGC -- Automatic Gain Control.
ALC -- Automatic Level Control.
Aliasing -- Audio or visual material after processing comes out predictably sounding or looking like something else that is perfectly valid although not correct for the situation. The most common example in movies is spoked wheels seemingly rotating backwards. If the wheel were really rotating backwards as seen in the movie, the filming would produce the same result (frame content);. More data is needed so the correct result can be obtained after processing. In the above example a faster frame rate is needed to make the actual forward rotation yield a unique set of frames which when projected would show the correct forward rotation.
ALiS (Alternate Lighting of Surfaces) -- A variation of plasma display technology where one horizontal electrode activates two rows of pixels alternately, giving higher brightness because of narrower gaps between rows of pixels for electrodes but also giving an interlaced appearance to the picture.
AM -- Amplitude Modulation.
American Wire Gauge -- Standard for measuring thickness of wires, associating a numeric value with a cross sectional area, with larger numbers applying to thinner wires.. (Stranded wire size corresponds to solid wire with an equivalent metal cross section, not the diameter of the bundle of strands.).
Analog -- Refers to systems that represent or encode or transmit information in a manner that is continuously variable, specifically not having to be rounded up or down to certain numeric values or being restricted to discrete pixel positions on a line. An analog picture reproducing system for example might reproduce any shade of red from a dark brown to a light pink while a non-analog system might only have twenty specific shades of browns, reds, and pinks to choose from. NTSC video is analog in the horizontal direction; details can occur anywhere along a scan line. It is not analog in the vertical direction; details that "fall between" two scan lines are lost or show up shifted slightly to fit on one of the scan lines.
Analog Component Video -- Refers to a standard consisting of analog video signals transmitted on three wires, one for luminance (Y) and synchronizing, one for the red component from which is subtracted the total luminance (R-Y) causing it to represent both red and cyan, and one for the blue component from which is subtracted the total luminance (B-Y) so it represents blue and yellow. (The green component is derived by combining the three components described.) These color definitions were chosen since R-Y and B-Y tend to zero leaving just Y for a black and white picture as the color tends to black, gray, or white. Also, recovering red, green,and blue is easy (R is an equal mixture of R-Y and Y) The designations Y/Pb/Pr and Y/Cb/Cr are also used to stand for analog component video where more correctly the latter is for digital video. The so called "component video" jack or jacks seen nowadays are for analog component video. See, also, Component Video.
Analog to Digital Converter -- A device or part of a device that converts analog signals (audio, video, etc.) into digital form.
Analog TV -- In broadcasting, refers to the analog video signal formats including NTSC, PAL, SECAM, and the original Japanese HDTV, where variations in voltages and phase represent the dark to light brightness range and different colors. In TV sets and also broadcasting and production equipment, refers to such equipment intended to receive (or produce/transmit) analog TV signals. It may be noted that some HDTV sets intended to show digital broadcasts contain no digital electronics for HDTV but rather require that the incoming video signal have been converted to an analog video signal by an external device such as a set top tuner box.
Anamorphic -- In video, means "Enhanced (or optimized) for 16:9 [shaped screens]". Generally refers to the uniform stretching or squeezing of an image so that it utilizes the entire area of a film frame with a different aspect ratio. The most common usage in filming has a 1.85 to 1 or greater wide screen movie "squished" on film with 4:3 aspect ratio frames. A special lens is used on the projector to exactly reverse this distortion and produce the correctly proportioned picture on the screen. "Anamorphic" in video is a misnomer. Video has no aspect ratio until it is displayed on the screen. The TV set or monitor determines the aspect ratio using settings specified by the viewer or sometimes automatically by taking some format data (not the picture data) from the video signal. More on anamorphic video including adjustment of TV sets.
Anechoic -- Without echo. An anechoic chamber is a room treated so that sound does not echo or reverberate within, and is sometimes used for audio testing or for audio recording where it is desired to give the impression of an outdoor performance.
ANSI -- American National Standards Institute, an organization which has established various standards for many different technologies. Video example: The ANSI contrast ratio is measured between the brightest and darkest subject matter that can be shown simultaneously, in the same image.
Aperture Grill -- See Shadow Mask.
Aperture Plates -- Mattes on a movie projector, manually adjustable.
Application, or App -- Software or program or set of programs for a computer or cellular phone or similar digital device, typically sold, downloaded, and/or installed as a single unit, and performing a single function or several closely related functions such as allowing you to control an audio or video system using a cellular phone. (Electronic hardware that may also be required is not part of an app.)
Artifact -- In video, refers to something present in the reproduced image, notably crawling dots, rainbow swirls, and color contamination, that was not present in the original picture or scene. Artifacts are the result of imperfect capture, processing, transmission, storage, and/or decoding of the video signal.
Aspect Ratio -- The ratio of width to height for a picture or screen. The original TV standards (NTSC, PAL, SECAM) are all based on a 4:3 (1.33:1) aspect ratio. This is approximately the Academy ratio which most movies prior to 1950 were shot. Wide screen movies were invented to attract moviegoers who would otherwise stay at home watching TV. The U.S. high definition TV standard calls for a 16:9 (1.77:1) aspect ratio. Several other aspect ratios are used in movie production, 1.85:1, 2.00:1, and 2:35:1 being common.
ATSC (Advanced Television Systems Committee) -- The organization that defined the U.S. 21'st century and some other digital television standards. The standards themselves may be referred to as ATSC or ATV (Advanced Television). The most common formats used are 480p (progressive scan frames of 480 rows of 640 or 720 pixels each); 720p which has progressive scan frames of 720 rows of 1280 pixels, and 1080i (540 rows of 1920 pixels each to be interlaced and using 1080 scan line positions). These formats have approximately 24, 30, or 60 frames per second (progrssive formats) or approximately 60 fields per second (interlaced formats).
Attack -- The first part (which may be thought of in terms of milliseconds) of a particular sound such as a note sounded on an instrument, including any rise to peak amplitude (or intensity) and, if a steady or gradually declining amplitude portion follows, includes any rapid drop from the peak amplitude to the vicinity of the sustained portion.
ATV -- Advanced Television. See ATSC.
Audio-Visual (A/V) Jacks -- Refers to the jacks and connections (if any) on a TV set other than the antenna connections. So named because they were originally used by the audio-visual aids personnel in schools to connect closed circuit equipment, cameras, and video tape recorders.
Audio/Visual Receiver (or Audio/Video Receiver) -- An audio amplifier with radio tuner(s) (FM stereo and sometimes AM standard broadcast), sometimes a pre-amplifier for a phonograph pickup, tone controls, a number of auxiliary audio and video jacks, and a means of selecting any one of the inputs or audio sources together with the matching video source if any. Generally the selected video signal is not processed in any way; it is simply passed to the video output jack or cable.
Automatic Frequency Control -- Circuitry in a tuner that compensates for drift in the tuning characteristics of a tuner (perhaps due to heat) or even compensates for drift in the frequency transmitted by a station, thus keeping the station tuned in correctly. Sometimes AFC identifies a particular frequency transmitted by a station specifically for AFC purposes and locks the receiving circuits onto that frequency..
Automatic Fine Tuning -- A form of automatic frequency control for TV sets that eliminates the need for a separate fine tuning control to be used each time the channel is changed.
Automatic Gain Control -- -- Circuitry in an amplifier that causes the amount of amplification (gain) to vary inversely with the level of the input signal. It is common in the RF circuits of tuners so that weaker stations can be received reasonably well while stronger stations do not overload the amplifier stages.
Automatic Level Control -- Another term for automatic gain control as it applies to the recording circuits of tape and disk recorders. It optimizes the input signal level for the dynamic range of the recording media so the user does not have to make manual settings or adjustments in casual situations. (Professional recording requires manual setting of record level.)
Automatic Volume Control -- Another term for automatic gain control as it applies to audio circuits It is used in a TV or radio receiver so that weaker stations tuned in play with approximately the same loudness as stronger stations without adjusting of the volume control.
AV -- Audio and visual, or audio and video.
AVC -- Automatic Volume Control.
AWG -- American Wire Gauge.
B-Frame (bidirectional) -- In a video compression scheme, a frame for which enough data is stored so that overlaying the data atop either the complete frame after or the complete frame before will yield the subject frame. Useful for single step backwards. See, also, I-Frame, P-Frame.
B-Y -- The blue color component from which has been subtracted the total luminance (Y) This component is used instead of plain blue (B) so it would tend to disappear (approach zero) as the actual color tends towards white or gray. This maintains compatibility with black and white TV and results in fewer artifacts in black and white pictures. See, also, Prime Disclaimer. B-Y, and also R-Y, are used for a variety of purposes during video signal processing, transmission, and storage. The (sub)signals Cb, Pb, and U are approximately the same as B-Y (and Cr, Pr, and V are approximately the same as R-Y), there being slight proportioning differences.
Back Porch -- In analog video, the few milliseconds of zero signal level at the end of the Horizontal Retrace Interval, or just before the picture information for a scan line begins. Often used to establish a reference for black level.
Bad Edit -- Departure from the cadence (3-2 pulldown for NTSC and 24 fps film) of repeated film frame content in the sequence of video fields or frames, most likely to be found at a scene change.
Balanced Circuit -- A circuit in which neither the "positive" or "hot" conductor nor the "negative" or "return" conductor is grounded (both conductors are "hot") and where the positive to ground voltage and ground to negative voltage should be the same. Balanced cabling of low level signals such as microphone inputs tends to acquire less noise since any noise would be picked up equally by both conductors, be out of phase in one conductor relative to the other and thus cancel out in the overall circuit.
Balun (Balanced Circuit to Unbalanced Circuit Transformer) -- A device used to connect a circuit (unbalanced) one of whose two conductors is grounded to a two conductor circuit (balanced) neither of whose conductors is grounded. A typical example of use in video products is a 300 ohm antenna cable (balanced) connected to a 75 ohm antenna cable (unbalanced).
Banana Plug and Jack -- An press fit electrical connector whose plug has a metal prong about 3/4" long and 3/16" wide, usually made of springy metal and which prong shape suggests a tiny banana. Used where it is necessary or desirable to disconnect and reconnect audio or low voltage wires frequently.
Bandwidth -- (1) A measurement of the ability of a system or circuit or cable to carry or handle a broad range of frequencies with reasonable uniformity. The single word "bandwidth" refers to the frequency range (starting at zero hertz or DC if not otherwise specified) where the frequencies reproduced worst are output with at least 50% of the strength of the frequencies reproduced best. More technically the output voltage must be within than -3 dB of the maximum output given constant volts in. Standard DVD video output (interlaced NTSC) requires 6.75 megahertz of bandwidth. Click here for more on bandwidth. (2) Colloquial term for "needed overall capacity or consumption" without regard to (uniform) frequency response, as in "if one TV channel occupies 6 MHz, then three TV channels occupy 18 MHz". This analogy has been extended to such topic contexts as "automobiles require more bandwidth (in terms of road space) than bicycles to carry a given number of people".
Barn Doors -- Pillarboxing. Display of a picture narrower than the screen's aspect ratio with unused stripes at the sides of the screen.
Bass Dump -- Speaker system intended to handle low frequencies at relatively high volume (high power levels) and which may or may not also have the duty of reproducing mid-range frequencies, for example being the only speaker system for a guitar.
Bass Reflex -- Speaker cabinet with an opening relieving air pressure behind the woofer and allowing sound waves generated behind the woofer to contribute to the overall output, but with partitions or baffles inside lengthening the travel path of escaping sound waves so they emerge more in phase with sound waves from the front of the woofer.
Bass Shaker -- Audio transducer (actually a voice coil and magnet assembly similar to that in a loudspeaker) to be attached to the (not absolutely rigid) floor or to furniture to give a vibrating sensation to the viewer(s) concurrent with low frequency sounds from the speaker systems and make a movie seem more live.
Bayer Pattern -- Arrangement of pixels in a camera sensor in 2x2 blocks where two pixels diagonally opposite one another represent green and the two remaining pixels represent red and blue, respectively. The luminance value for each pixel is interpolated taking into account adjacent pixels, sometimes including pixels in adjacent blocks ,and based on the formula Y (luminance) = 0.6G + 0.3R + 0.1B (or similar). Named after its inventor Bryce Bayer.
Beaming -- A tendency of a speaker to direct its output narrowly, in one direction. If present, it is most pronounced at higher frequencies.
Betamax -- Trademark of the Sony Corporation that refers to certain of their now obsolete VCR's. Sometimes used to refer to any VCR since the Sony units were first to appear on the consumer market.
Bi-Amplification; Bi-Amping -- Having separate (not sequential) amplifier stages for different frequency ranges, usually a two way split for mid-range/treble, and bass. One advantage is reducing some distortion resulting from interaction among different frequencies (including intermodulation distortion). The separate amplifier outputs must not be connected to the same set of speaker terminals even if there is a crossover network in the speaker system.
Bi-Wiring -- Connecting one cable from the amplifier output terminals to the woofer of a speaker system and connecting a second cable from the same output terminals to the mid-range and tweeter speakers. Crossover networks are still needed. While it is not intuitive how running two sets of wires all the way from the amp. instead of one thicker set splitting off at the speaker system can improve the sound, it is true that a loud bass passage can result in a slight voltage drop within the wires going to the woofer.
Bias -- (1) A DC voltage or offset superimposed upon a video or audio or radio frequency signal that is otherwise a form of alternating current, the most common usage is to convert AC to pulsating DC because an amplifier stage requires input to be in such a form. (2) A DC voltage or offset or a higher frequency AC voltage superimposed on an audio or video signal to facilitate recording on magnetic tape.
Binding Post -- An electrical connection consisting of a threaded stud and a nut or other screw-down fastener to hold wire ends in place and maintain good electrical contact.
Bipolar (as opposed to Dipolar) Speakers -- Refers to a speaker system with similar speakers facing both the front and the rear of the cabinet, and where the speakers are wired in phase, that is, all cones move outward at the same time or inward at the same time.
Bit (Binary Digit) -- The smallest piece of information in a digital system or environment or context, which piece can have one of two values (off/on, 1/0, yes/no). 8-Bit, 24-Bit, etc. -- One measure of resolution or depth or accuracy where more usually means better and where two bits can represent four different values (off-off, off-on, on-off, on-on), eight bits can represent 256 different values, 24 bits can represent just over sixteen million values, etc.
Bit Rate -- Also, a measure of maximum data handling capability that can be applied to some parts of a digital system, where more usually means better, for example 28.8 kilobits per second or six megabits per second.
Bit Stream -- Data transmitted one bit at a time (sequentially).
Black Crush -- Burying of shadow detail because the video system does not achieve visible differences among what should be different shades of very dark gray. It may be the result of less than optimum calibration, or a design defect.
Black Level --(1) The voltage level or visually perceived shade of gray that represents black or is declared to represent black in video material. (2) The "brightness" control on a TV or other video device. Adjusting this control fundamentally controls what level of illumination on the screen corresponds to black but the levels of illuminations corresponding to white and all shades of gray should also vary in like fashion, subject to equipment limitations, so the overall brightness of the picture varies.
Blacker Than Black -- Refers to video content recorded or processed using levels below the defined level for black, for example (for DVD) less than 16 on a scale of 0 to 255 (8 bits) where, also, white is 235, or (for U.S. NTSC broadcasts) less than 7.5 on a scale of 0 to 100 (IRE units). Usually it is not technically practical to eliminate blacker than black content completely. Ability to distinguish blacker than black content should not be part of the presentation but some movie producers and directors use blacker than black intentionally.
Blackout Cloth -- A quite smooth closely woven fabric with a (usually flat white) opaque coating that can make it very suitable for use as a projection screen that did not dissipate the projector's light output out the far side. Its original purpose was making reasonably attractive window shades that did not let interior light be seen from outside a building.
Blanking Interval -- See Horizontal Retrace Interval, Vertical Retrace Interval. So named because the electron beam in a CRT is supposed to be shut off during this interval (time span) so as not to make stray marks on the screen as the beam is returned to the left side of the screen or top of the screen.
Blooming -- The slight thickening of scan lines as seen on a CRT screen when the electron beam intensity increases beyond a certain point. It is desirable to set the contrast low enough so that blooming does not occur.
Blooper -- An error in the production of a motion picture detracting from the viewer's impression of viewing live action in its proper setting. Examples include microphone booms not part of the subject material in the field of view, an electric light in a scene depicting a time period before the discovery of electricity, a character pulling on a rope supposedly attached to something but the view is such that the rope is seen continuing on towards something else, and characters appearing in different clothing in the next scene where in the sequence of events a clothing change could not possibly have occurred.
Blu-Ray -- Trademark for a DVD with larger data storage capacity together with players and recorders, used for high definition video. So named because the laser used for playback and recording is of a higher frequency, giving off a blue light compared with the red light of CD player and ordinary DVD player lasers.
BNC -- Refers to a round coaxial one conductor plus ground plug and jack assembly. The jack has a cylindrical "bayonet" shell a little larger around than a pencil (about 3/8 inch) and a center hole that a paper clip wire would just fit (1/32 inch). The plug has a thin matching center pin which may be the center conductor itself of a coaxial cable. The outer shell of the plug fits over the jack shell and is locked in place by a quarter turn twist to engage protrusions on the jack shell. BNC connectors preserve the 75 ohm impedance of a circuit better than RCA connectors which also have a center pin and outer shell coaxial format. There are several stated origins of the name: Bayonet Neill-Concelman (after its inventors?); British Naval Connector; Bayonet Nut Connector.
Bob -- Method of line doubling where an intervening scan line is synthesized (its content interpolated) using its neighbors. Apparently so named because under some conditions the image appears to vibrate (bob) up and down. A disadvantage of using bob exclusively is that the picture is not as sharp as it could be. See, also, Weave.
Bookshelf Speaker -- Generally refers to apeaker system containing a woofer or full range speaker (not necessarily a subwoofer), and whose cabinet is generally less than 18 inches long and 12 inches wide, namely which can sit in most bookshelves lying on its side.
Boomy -- Refers to sound with an (over)abundance of content around 80Hz (mid-bass; not the lowest audio frequencies). This quality was characteristic of juke boxes and other applications where "more bass" was desired to give a good "thump, thump" but the audio power and loudspeakers were incapable of delivering much output in the lowest audio range.
Boost -- Amplify, usually in the context of amplifying some frequencies such as bass frequencies more than other frequencies. Antenna Booster -- Amplifier placed in the signal path from an antenna to amplify the signals from weak or far away broadcast stations.
bps -- Bits per second. (With a capital B, bytes per second.)
Breathing -- Noise, including hiss and hum, varying in volume. May be quite evident when softer passages along with any accompanying noise are boosted at playback time to improve intelligibility at the expense of sacrificing dynamic range.
Bridging -- Configuring of an amplifier so that two or more sound channels intended to drive separate speaker systems can drive a single speaker system via the same set of speaker terminals and with close to if not all of their combined power output. Bridging must not be attempted unless the amplifier is specifically capable of doing it, otherwise damage can result.
Brightness Control -- See Black Level. This control, although its purpose is to set the level of black subject matter, should also change the displayed intensity of white subject matter and of matter of all intervening shades of gray by the same amount.
Brilliance Control -- Control in a speaker system that varies the signal level applied to the tweeter. (The woofer signal level is seldom controlled.)
Broadcast Flag -- Information that can be included in a broadcast to notify receiving equipment that the material broadcast is under copy protection and that the receiving equipment should process the material specially so as to inhibit making of unauthorized copies. One standard, called HDCP, for receiving equipment is intended to prohibit the exposure of copy protected material in any unencrypted manner including in any analog format.
Burn-In -- (1) Permanent darkening or discoloration of all or part of the phosphors on a CRT or in a plasma panel actually caused by excessive heat which in turn resulted from very strong or prolonged excitation due to bright subject content. (2) Part of the testing procedure for new electronic equipment where the equipment is left powered on for some time period, the reasoning being that electronic equipment that has a weakness or defect is most likely to fail very early in its life.
Bus -- Group of wires or lines interconnecting several sub-components of a computer -- central processing unit, memory, hard disk controller, etc. -- so that if any sub-component should place data on said lines, any or all other sub-components can easily and almost instantly retrieve said data. Plural: busses. A computer may have one bus interconnecting the central processor and memory and have another bus connecting an input-output controller to a jack where an extension of the bus can be made via cable to an external device such as a digital camera. Bus Bar -- One of the current carrying metal strips in an electrical panel which circuit breakers are clipped onto, or a heavy bare wire or similar metal strip in a panel or a channel (trough; raceway) performing a similar function of distributing power to multiple loads or branch circuits.
Byte -- A group of five to ten, usually eight, bits used to represent one textual character or a single numeric quantity. Also, any one group out of groups of the same number of consecutive bits taken from a bit stream coming down a single line. Also, a group of bits taken one per line from data transmitted in parallel fashion over 5 to 10 lines..(A group of 3 or 4 bits is often referred to as a "nybble" and a group of more than 10 bits is often referred to as a "word".)
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