Television and Video Glossary -- C-D
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
C -- The color, or chrominance, signal representing all colors and already modulated onto a subcarrier as if to be combined with a luminance signal to become composite video. Its amplitude represents the color intensity (saturation) and certain phase relationships represent the color itself (hue). Unlike with the simplest and most common amplitude modulated signals, the sidebands of the C signal are not mirror images.
CAV -- Constant Angular Velocity. Also Component Analog Video or Y/Pb/Pr; where we have used instead the term Analog Component Video, q.v..
Capacitance Effect Disk (CED) -- Also referred to as "RCA Selectavision" video disks. This was a 12 inch video disk and player system marketed by RCA, and now obsolete. It did not have consumer recording capability. No laser was used; the disks were grooved like (pre-CD) phonograph records, and the video signal was recorded as rising and falling ripples ("hill and dale" in older phonograph terminology). The needle, or stylus, does not follow the ripples exactly, it is not small enough or given enough pressure to. Under current technology it is impossible to make a stylus small and light enough at reasonable cost to do so. Instead, the rapidly varying tiny air space between the stylus and the groove bottom is sensed (using capacitance) to derive the video signal. According to specifications, the disks give about an hour's playing time on a side with about 240 lines of horizontal resolution. One revolution of the disk corresponds to four video frames. The disk is never seen or touched in normal use. The viewer inserts the rigid jacket (caddy) into the player and then withdraws it leaving the disk behind. To unload the disk, the jacket is inserted again.
Carnival -- See Funhouse.
Cartridge -- (1) A small flat container that holds magnetic tape (or film), generally referring to such containers with one spool and with the tape as a (n endless) loop or with the tape revealing an exposed end treated so that can be automatically withdrawn and threaded into an external mechanism. (Tape cartridges with both supply and takeup spools are referred to as cassettes.) (2) The small assembly at the end of a phonograph arm that holds the stylus (needle) and that converts the vibrations of the stylus into an electrical signal.
Cassette -- A small flat container that holds magnetic tape in a ready to use state (without the need for manual threading but not implying automatic rewinding), generally with both supply and take up spools contained within.
Cathode Ray Tube -- Electronic vacuum tube in which a thin beam of electrons is shot through the space inside and against the far wall (faceplate; screen) or against a plate inside.. This includes all picture tubes used in older TV sets or computer monitors.
Cb, Cr -- Refers to the color component video signals B-Y and R-Y respectively optimized for digital purposes or transmission. In an 8 bit system Cb is equal to B-Y but offset so the minimum value is 16 and scaled so the maximum value is 240. Cr is equal to R-Y similarly offset and scaled. Sometimes Cb and Cr are loosely used to refer to B-Y or Pb and R-Y or Pr in any context. The (analog) component video jacks on some video equipment may be labeled Cb and Cr rather than the correct Pb and Pr.
CCTV -- Closed Circuit TV (system).
CD-R (Compact Disk, Recordable) -- Refers to compact disks that can be recorded one at a time, or the equipment used to make the recordings. The so-called CD-R disk can only be recorded once; although, depending on the recording method used, additional material can be recorded later on the space remaining. The disks themselves are constructed differently from ordinary non-recordable CDs. Ordinary CDs are stamped like grooved records, and then the silver or gold reflective layer applied. Recordable CDs have the foil layer (gold colored) already applied, and the recording consists of "burning" the pits one at a time into an intervening layer of organic dye. "The jury is out" as far as the longevity of these disks goes; to this writer the organic content suggests possible aging problems that color film today still has. Not all CD players can play all brands of CD-R disks since the reflective surface may have a different color from the usual silver or gold.
CD-RW (Compact Disk, Rewritable) -- Recordable compact disks similar to CD-R disks but which permit an unwanted recording to be recorded over.
CECB (Coupon Eligible Converter Box) -- ATSC digital TV tuner box that qualified for the U.S. government sponsored $40. purchase discount. It must have certain features needed to receive and reformat digital TV broadcasts for anyolder (analog) TV set. It must downconvert "downrez" the video to standard definition and must not have various advanced features associated with HDTV.
CED -- Capacitance Effect Disk
CEMA -- Consumer Electronics Manufacturers' Association.
Central Processing Unit -- (1) In a computer, the digital circuitry, usually contained in a single integrated circuit chip but which could also occupy all of a refrigerator sized cabinet, where the bulk of the processing takes place or, if processing takes place in several locations, the circuitry where the supervisory processing takes place. (2) The box or piece of equipment containing the central processing unit circuitry.
CES (Consumer Electronics Show) -- A large trade show, usually held in Las Vegas, Nevada, open to the public, where new electronic equipment is exhibited and demonstrated.
Chapter -- Program material subdivision on a laserdisk or DVD that a player can easily advance to, analogous to a band representing usually one musical selection on an LP record or a track representing usually one musical selection on a CD.
Chroma Bug -- See Chroma Upsampling Error
Chroma Delay -- Slight horizontal shifting of color relative to the luminance details of the picture giving the appearance of a poorly done child's coloring book. It results from less than perfect circuitry or cables where literally the color subsignals take a longer or shorter time to arrive at the picture tube or other video display element. As seen it can be mistaken for convergence errors.
Chroma Phase Control -- Another name for "tint control" or "hue control" in analog video equipment.
Chroma Upsampling Error -- Condition where, (for every four scan lines) shared color content that belongs to lines 1 and 2 is extracted with the odd interlaced field and gets applied to lines 1 and 3, and the shared color content that belongs to lines 3 and 4 is extracted with the even field and gets applied to lines 2 and 4. The result can show up as thin discolored streaks. Some DVD players and HDTV tuners can apply the color correctly, some hide the error by blending adjacent scan line color content, many players including some upscale models and some progressive scan models don't hide the error. Click here for more details.
Chrominance, or Chroma -- The portion of the video signal that represents color. It is not very useful by itself; if so used, it would produce a colored image but all the colors would be the same intensity. For example all shades of red from a dark brown to pink would show up as the same red. Chrominance signals are usually a pair, as if to permit graphing all the possible colors in two dimensions, such as on a color wheel. One example (NTSC I/Q signals) can be visualized graphically as orange to the right, green to the top, blue to the left, and purple to the bottom, with other colors in between. Click here for more on color. We use the terms Chrominance and Chroma interchangeably (not quite correct) on this web site; those readers who know the difference between them may refer to Prime Disclaimer, q.v.
CIE , Commission Internationale d'Eclairage -- Committee which in 1931developed a numeric model for expressing color as perceived by the human eye. The model depicts hues along the perimeter of a triangularish curved top Chromaticity Diagram permitting the use of X-Y coordinates to represent colors. Violet is at the lower left, blue is at left center, green is at the top left, yellow is near right center, and red is at the lower right with wavelength in nanometers marked along this part of the perimeter.. More saturated (deep) colors are at the perimeter and less saturated (pastel) colors and white are near the center. If any three colors such as for red, green, and blue cellophanes or phosphors in video equipment were chosen, a triangle with these colors at its corners drawn within the CIE diagram encompasses all of the colors that can be reproduced by mixing light from three sources with those three colors respectively, colors outside the triangle can only be approximated.
CIH; CIW -- Constant Image Height; Constant Image Width, q.v.
Cinema 4K -- Because "4K" is so often used nowadays to refer collectively to video formats with roughly 4000 pixels horizontally, including 3840 x 2160 Ultra High Definition, video professionals and motion picture production staff often use "Cinema 4K" to refer to video formats with a full 4096 pixels horizontally to which "4K" originally referred to.
Class (as in 47 Class, 24 Class) -- The size of flat panel direct view TV sets may now be advertised as rounded to the nearest inch, as 47 Class for a 46.8 inch or 47.4 inch set.
Class A Amplifier -- An amplifier or amplifier stage that conducts current (delivers a non-zero output) all of the time. Some of its characteristics are: (a) it consumes the same amount of power regardless of whether, for example, an audio signal represents a loud or soft passage, (b) one amplifying element (such as a tube or transistor) can reproduce the entire signal (waveform) without significant distortion, and (c) it produces an output centered around a DC voltage ,that is, an output with a DC bias applied, or that is, an output that is a pulsating DC as opposed to AC. Class B Amplifier -- An amplifier or amplifier stage that amplifies just the positive portions or just the negative portions of the input waveform, delivering a zero output during the other 50 percent of the time. Some of its characteristics and restrictions include: (a) it consumes less power when, say, an audio signal is soft, (b) for audio, two amplifying elements are needed, one for the positive parts of the input waveform and one for the negative parts of the input waveform, (c) the output usually does not have a DC bias applied, and (d) for audio, careful design is needed to minimize distortion (crossover distortion) most noticeable in soft passages due to non-linearity where one amplifying element stops conducting and the other one starts conducting every half cycle. Class AB Amplifier -- Amplifier stage that delivers a non-zero output for more than half of the time but less than all of the time. This class is often used for audio amplifiers to further reduce crossover distortion. For that part of the audio waveform near zero, which encompasses all of the audio signal during soft passages, both required amplifying elements are delivering non-zero output. (Both elements deliver outputs with DC biases applied.) Class C Amplifier -- Amplifier stage that delivers non-zero output less than 50% of the time. Used for certain non-audio applications such as radio transmission where added efficiency can be attained compared with class B amplifiers. For audio applications, preamp and intermediate amplifier stages are usually class A while the power amplifier (final) stages are usually class AB.
Cliff Effect -- The sudden loss or significant degradation of the picture and/or sound of a reproduced or received digital program when data loss due to such factors as marginal over the air reception goes above a certain amount.
Clipping -- Overloading of a system, for example video or audio circuitry, where while for the most part as the input increases or decreases (in intensity or loudness or brightness) the output does so in like fashion, at some level of input (where overload occurs), further increases in the input do not cause a continued increase in the level of the output. Clipping can be described easily graphically by drawing waveforms, where peaks are literally clipped off a certain distance from the center line or zero line.
Clock-In -- A common method of converting an analog signal to digital. Since an incoming analog video signal also arrives one pixel at a time, it is sampled at fixed time intervals (in nanoseconds). Essentially the signal is chopped up into little pieces, much as a chef may chop carrots or celery or bananas into slices. Clocking in has the shortcoming of sometimes taking the last half of one pixel and the first half of the next pixel (pixel straddling) as a new pixel when the incoming analog video was digital at some earlier time; the former pixel footprint remains. This results in loss of horizontal resolution. Interpolation may occur naturally during clock-in and the result varies depending on whether the digital value (sample) is derived from the entire slice (averaged) or only a small portion of the slice. (Additional interpolation may or may not be done later.)
Closed Circuit TV -- TV or video system where the program source (camera, VCR) is connected to the video display (TV set) by wires. Just about every home theater contains a closed circuit TV system.
CLV -- Constant Linear Velocity.
Coax (Coaxial Cable) -- A round cable where one of the conductors is a thin wire running down the middle and one conductor (usually grounded) is a cylindrical shell or braid that surrounds the first conductor. Some "two conductor plus ground" cables have two thin wires running down the middle. Other cables have one wire in the middle surrounded by two concentric shells. Coax cable is often used to connect video components. The insulating material that keeps the center conductor centered determines the quality of the cable and/or the kinds of video signals that the cable can carry without degradation. Some people reserve the words "coax cable" to refer to the round 75 ohm cable that carries multiple modulated TV signals from an antenna or cable TV system.
Color Depth -- One way of referring to how many colors a system can reproduce, usually expressed in terms of bits, for example (for one particular color) 8 bits for 256 different shades of that color or (all colors) 16 bits for 65 thousand different colors.
Color Difference Video -- Analog Component Video q.v. So named because the color components consist of the mathematical or electronic difference between other commonly seen video signal components, for example red content minus luminance.
Color Gamut -- All of the different colors that can be produced with a given group of (usually three) video subsignals feeding video display element(s) together with appropriately colored phosphors or colored cellophanes in the respective display elements.
Color Space -- A group of three video subsignals which together represent all possible colors and luminances within limits. In video the most common color spaces encountered are RGB (red to black content, green to black content, blue to black content) and Y, R-Y, B-Y (roughly red to cyan content, "white to black content", and roughly blue to yellow content).
Color Temperature -- In video, a measure of whether or how much "white" has a bluish or yellowish or reddish tinge, expressed in degrees Kelvin (K, here). The video standard is 6500K but requires test equipment to precisely measure the required amount of red, green, and blue content. Technically, only certain colors are on the Kelvin scale. They range from reddish to yellowish to bluish , skipping green, as produced by a certain material (carbon?) glowing upon being heated to the respective temperature in K. In practice, other similar colors such as from fluorescent lights (which may have too much green) are occasionally assigned color temperatures in K. A typical incandescent lamp delivers about 2500K, daylight is about 6500K.
Color Under -- A method of recording video to tape including recording in the VHS, Beta, and 8mm analog formats. The chrominance is quadrature modulated on a subcarrier much as for composite or S-video, but occupies the lowest frequencies, typically around 650 KHz as opposed to the usual 3.58 MHz. The luminance is also modulated on a subcarrier (frequency modulated) and occupies the remaining available, higher, frequency range. The lower subcarrier frequency for the chrominance reduces discolorations due to phase errors in turn due to less than perfect tape motion.
Coloration -- Any distortion occurring in, or change from, the original source when audio is reproduced.
Colorizing -- The adding of color (usually involving artistry) to what was once a black and white (or monochrome) photograph or motion picture.
Comb Filter -- In analog video, an electronic filter used to separate luminance and color information from a composite video signal. (Color and luminance must subsequently be recombined in a different way, namely we isolate red, green, and blue content and then blend these three, to produce the picture.) The comb filter is so named because it has a frequency response which when graphed suggests the teeth of a comb; the filter alternately accepts and rejects small bands of frequencies "as we progress up the scale". One way of visualizing what a comb filter does is to draw evenly spaced parallel lines, alternately red and black, on paper, and then look through a comb held so as to hide all of the black lines. Such an array of lines could (and does) stand for the luminance and color content of a composite video signal and comb filters are used in the medium grade to more expensive TV sets to perform the necessary task of separating the two. Notch and bandpass filters, common on lower priced TV sets as an alternative, produce acceptable pictures but with more minute discolorations and limited horizontal resolution. Click here for more discussion on comb filters.
Combi (with a short "O") -- Refers to a disk player, usually a laserdisk player, that can play disks of different formats, for example both laserdisks and DVDs.
Combing -- The feathery or ghost like double exposure effect caused when non-matching (due to subject motion) odd and even interlaced fields are woven together to form a full frame of video which is then displayed as progressive scan on the screen. While it can also be seen during interlaced scanning, it is less noticeable here on a CRT because the odd lines are starting to fade as the even lines are being drawn, and vice versa. Combing is neither caused by nor alleviated with comb filters.
Comet Trails -- A form of motion blur. As a bright object moves over a dark background (or sometimes vice versa), a fading ghost of it trails behind. Caused by slow changing of light to dark (or vice versa) usually inherent to the display and most likely encountered with some CRTs and some LCD displays.
Commercial Skip -- Refers to a variety of video recording and playback technologies that reduce the amount of time spent playing commercials. Some techniques pause the recorder when it appears that commercials are being broadcast. Some technologies cause a video player to fast forward past commercials. Some technologies sense flags broadcast along with commercials used by other equipment that monitors radio and TV stations to verify that commercials were aired per contract. One common method records the entire broadcast and the recorder then plays the recording back to itself while adding flags to cause automatic fast forwarding for the viewer. No commercial skip technologies to date are perfect.
Component Video -- In current usage, refers to Y/Pb/Pr analog component video , q.v. Not to be confused with Composite video. More generally, a video signal transmitted as at least three separate components (subsignals) using separate wires or cables if analog. The most common formats are: RGB (separate signals for red, green, and blue), and Y/Pb/Pr, (luminance together with a signal based on blue and a signal based on red). Using simple circuits, RGB needed to display a picture can be easily derived from the latter. In order to get RGB using simple circuits, there must be at least three components supplied. (In algebra, if a problem has three "unknowns" there must be at least three equations or relationships supplied in order to solve it.) S-video seemingly has two components, luminance and color, but the upper and lower sidebands of the (modulated) C signal together actually represent two sub-components. These together with the luminance make up the three components that simple circuits can in turn convert into RGB.
Composite Video -- Refers to an analog video signal where both the luminance component and the color component(s) are transmitted on a single wire or broadcast in a limited bandwidth. Each of the major analog systems NTSC, PAL, and SECAM has its own definition of how the luminance and color are combined and none are a simple commingling of red, green, and blue. The luminance and color information must be separated before the picture can be displayed.
Compression -- (Audio) The making of louder sounds softer and softer sounds louder during audio processing. The purpose is to raise the level of the softer sounds above the level of hiss or noise in the system and not have the louder sounds overload the system. (Video or audio) The digesting of a video/audio signal so it will occupy less storage space and/or require less transmission bandwidth, hopefully with a minimum of noticeable visible/audible deficiencies. This compression can be lossy, that is, it may be impossible to reconstruct the original video/audio signal exactly at the receiving end and/or at a later time.
Constant Angular Velocity (CAV) -- Refers to analog video laser disks which rotate at a constant speed (about 1800 RPM for NTSC) to play the program, where about 30 minutes of program fit on a side, and where the ability to do slow motion or single frames is easily accomplished and can be done by any player. One revolution corresponds to one video frame. If you examine the disk surface, you can see a bow tie texture pattern that represents the two interlaced fields and the vertical retrace intervals. There are some cheap tape recorders (Mini-cassette and 3 inch open reel styles) which use the constant angular velocity idea, using the take up spool only to pull the tape. As the recording or playback progresses, the tape speed past the heads increases due to the build-up of tape on the take up spool.
Constant Image Height; CIH -- Presentation style some home theater enthusiasts desire, where the picture is always the same height and the width is varied according to the aspect ratio. Also: Constant Image Width; CIW. A 4:3 TV set properly displaying movies of various aspect ratios is an example of a constant image width arrangement. If no special techniques are used, a 16:9 TV set is neither CIH nor CIW; 4:3 pictures are narrower and pictures of aspect ratio greater than 1.77:1 are less tall.
Constant Linear Velocity (CLV) -- Refers to analog laser disks where the rotational speed varies (1800 to 600 RPM) so that the amount of track circumference spanned by the laser beam is the same for each video frame. Since the circumference of each revolution of the spiral track near the outer edge (later in the program) is greater, the disk rotation is slowed down as the program progresses. A CLV disk holds about an hour's worth of program material on a side. Only the more expensive LD players can do slow motion or still frames when playing CLV disks, and usually only an even interlaced field or an odd interlaced field is seen at any given time. Incidentally the concept of CLV is used on all good tape recorders. You might observe that the cassette spool (or reel on an older machine) revolution speed varies. The take up spool mimics the behavior of the CLV laser disk, the beginning of the program's tape is at the center and the spool rotates fastes then. Audio compact disks are somewhat CLV in nature where the rotational speed changes but in steps rather than gradually.
Content -- Programs (shows), program material including individual performances, events, musical selections, news clips, and the like.
Contour -- An intentionally non-uniform frequency response, used for such purposes as reducing audible noise by boosting signal frequencies (usually the higher audio frequencies) prior to entering a stage (e.g. analog tape recording) that tends to have more noise at such frequencies, and including reversing the boost at a later stage (e.g. playback) where the accompanying noise is reduced as well.
Contrast -- The difference between the defined levels of white and black, either as seen on the screen or measured within the circuitry. In terms of calibrating a TV set, less contrast is needed when viewing is done with less room light. ANSI Contrast Ratio -- The light intensity ratio of the brightest to darkest picture details that can be showing (simultaneously and nearly juxtaposed) in the same image. On-Off Contrast Ratio -- The light intensity ratio of the brightest picture detail that can be shown in one scene to the darkest picture detail that can be shown in a different scene where such techniques as dimming of a projector lamp might have been used. Contrast Control -- The white level control; it should maintain black constant as it varies the level of white thus increasing or decreasing the range of in between light intensities used to represent the subject matter.
Convergence -- (1) The correct aiming of the three electron beams in a direct viewed picture tube or three separate pictures from three respective tubes in a projection TV (for red, blue, and green) to be together at all times. Without proper convergence, objects on the screen will have colored halos around them, white lines will seem to have a red, green, or blue line next to them, and resolution will be poorer. The most common reason for misconvergence in anlaog TV is the coils attached to the neck of the picture tube not in the proper position which usually takes a time consuming trial and error process to correct. Often perfect convergence cannot be achieved over the entire screen so a compromise where the errors are minimized but not completely eliminated must be accepted. It may be noted that a convergence error of one fifth of one percent means that one of the electron beams is off by a scan line causing a halving of the resolution at that spot on the screen. ("Convergence" for projection TV with several CRTs or miniature LCD pixel panels is also called "registration".) (2) The bringing together and integrating of two or more systems or technologies so that components can be shared. An example is the development and manufacturing of video monitors suitable for television, movies, and entertainment, and also suitable for computers and data display.
CPU -- Central Processing Unit.
Cross Color -- Spurious colored, mostly pinkish and bluish, swirls or streaks amongst or swamping out pinstripes and other fine picture detail, caused by small amounts of luminance signal present in the signal going into the color circuits. This situation is the result of imperfect Y/C separation by the comb filter (or notch and bandpass filters in less expensive TV sets).
Cross Luminance-- A grainy "zipper" effect along boundaries of colored objects on the screen or a silk screen effect within color patches. It occurs when color information in a composite video signal is not removed before the signal is passed on to the luminance circuits. This situation is the result of imperfect Y/C separation by the comb filter (or notch and bandpass filters in less expensive TV sets). where color information finds its way into the luminance circuits. When the zipper effect is moving it is often referred to as "dot crawl" When the "zipper" is "stationary" this same artifact is referred to as "hanging dots".
Crossover Network -- A circuit, usually passive, and often found in a speaker system, that allows for example just the higher frequencies to go to the tweeter and just the lower frequencies to go to the woofer.
Crosstalk -- Pickup or leakage of signal or information from an adjacent wire or from an adjacent circuit or from an adjacent track or groove on a recording. Channel separation is another way of saying freedom from crosstalk.
Crystal UHD -- Ultra high definition or 4K TV with the usual LCD pixel stencil layer to create the luminance (lights and darks) of the picture and an LED illuminated back light panel. The designation "Crystal" may also be found with 1080p and other TV screen grades or resolutions.
CRT -- Cathode Ray Tube.
CUE -- See Chroma Upsampling Error.
CVBS -- Composite video.
D/A -- Digital to analog.
DBX or dbx -- A company that manufactures audio compression and expansion circuitry. Also refers to the circuitry itself and the technology the circuitry represents. The purpose of the circuitry is to reduce noise by raising the level of softer passages during recording so these passages are well above the noise level inherent to the recording medium, and restore the original dynamic range at playback time.
DCDi -- Trademark of Genesis, Inc. for its proprietary de-interlacing techniques including smoothing out diagonal lines and edges, and handling of film source video with imperfect 3-2 pulldown. The technology was invented by Faroudja Laboratories which was acquired by Sage, Inc.which in turn was acquired by Genesis, Inc.
DCI - Digital Cinema Incentives -- A group representing various movie studios including Walt Disney, Universal, and Warner Bros. which developed standards for digital movie production including use of 2K and 4K video formats.
Datacasting -- Transmission of data not a direct part of and not necessarily related to the video program, within the video signal, perhaps within the horizontal or vertical retrace intervals. Usually the data has some relationship to the program such as being extra sports commentary or closed captions.
Deep Color -- Generally refers to digital video formats with more than 8 bits (typically 10 or 12 bits) per component (Y, Cb, Cr, R, G, B, etc.). More data values allow a greater range of color shades to be represented thus not having visible steps or banding (posterization) in what should be a smooth gradation of color shading.
De-Interlacer -- Device or circuit to convert interlaced video to progressive scan video with the same number of scan lines per full video frame. Loosely referred to as a line doubler. Although "outputting each scan line twice" will produce video of the same format as video that was originally progressive scan, "de-interlacer" should refer to devices with more sophistication to make a picture that at least partly has the appearance of having been originally recorded or televised as progressive scan. This typically involves interpolating parts of new intervening scan lines using the original neighboring scan lines and using parts of scan lines from the previous and/or next field. More on de-interlacing.
Decade -- (1) A tenfold increase. (2) A frequency band consisting of any starting frequency extending up to a frequency ten times the starting frequency. In an electronic context it is used to describe a filter's behavior such as attenuating ten dB per decade. Decade Box -- A test module providing variable resistance, capacitance, etc. where adjustments are in increments equal to decades, sometimes with reasonable intervening increments such as 1, 2, 5, 10, 20, 50, 100, 200, etc. ohms, microfarads, etc.
Decay -- The fading to silence or black (respectively) of the sound from, say a plucked string or the light from phosphors (respectively) after stimulation such as from plucking or from the electron beam (respectively) ceases. (2) The portion of the graphical representation over time (usually milliseconds) of a sound wave or light intensity that represents fading to silence or black..
Decimate -- To discard some of the information in a sense of omitting a little here, a little there, for example discarding or blending with its neighbor every fourth scan line during video format conversion, but not in the sense of editing out scenes from a movie. (2) Literally, to discard or remove ten percent, or one part out of every ten parts.
Diaphragm -- The vibrating part of an audio transducer (exclusive of a voice coil or crystal) that captures acoustic energy for conversion into an electrical signal or that moves the air to create acoustic energy from an electrical signal. For a speaker the diaphragm is the cone (and/or dome if any or sometimes a ribbon). For a bass shaker the diaphragm is the surface to which it is attached. All headphones and microphones also have diaphragms.
Digital -- Being expressed or represented as a series of numbers. Since sound can be graphed on paper as a waveform, it can in turn be described numerically little by little as the distance of each portion of the drawn waveform from a baseline (X-axis) Sounds and pictures can be recorded, stored, and played back digitally with no distinguishable difference from the original if enough numbers, or samples, are used. In practice, due to the limited storage space (on tapes and disks) and limited transmission space (bandwidth) compromises have to be made. For video this shows up as the limitation of detail in a picture to be made up using an array of independently colored dots, say, 720 across by 480 high (DVD standard here).
Digital Cable -- Refers to cable TV where the signals are in digital form when transmitted via the cable. Usually this permits transmitting and offering more channels than an analog cable system may be able to. The programs may or may not have been analog as originally produced and may or may not be of higher quality.
Digital Micromirror Device (DMD) -- Digital video display technology for projection TV consisting of a small panel typically about an inch square with rows of microscopically small mirrors that physically tilt under electronic control to aim light towards the screen or off in some other direction to be absorbed. Gray shades are obtained by vibrating the mirrors back and forth with different duty cycles. In its heyday (2008) due to the cost of DMD display elements, a TV using this technology typically has only one DMD panel which alternately produces red, green, and blue picture content. A wheel with red, green, and blue windows and sometimes a clear window spins in the light path in synchronism, or arrays of red, green, etc. LEDs as light sources illuminate in synchronism to flash sub-images forthe respective color content on the screen in sequence and generate the full color picture.
Digital to Analog Conversion -- The construction or reconstruction of an analog signal given a digital representation of that signal.
Digital Tuner -- The channel selector for digital broadcasts (the ATSC tuner for over the air HDTV and DTV in the U.S.).
Digital TV Monitor -- Refers to a TV set intended to display programs broadcast as digital but without a channel selector for the digital broadcasts.
Digital TV Set -- In the marketplace this term is used to refer to a TV set that can display U.S. HDTV broadcasts without conversion to standard definition. Actually a few older HDTV sets use all analog processing for HDTV, they have no HDTV tuner built in and the HDTV video signal fed from an external tuner must been fully decoded and converted to analog. Meanwhile the best display of "analog" broadcasts requires digital components, namely the comb filter and sometimes a de-interlacer and/or scaler. If the TV set uses LCD, LCoS, DMD, or plasma display elements, video processed as analog must be converted (back) to digital form . Digital TV -- Refers to standard or high definition TV program content that is in digital form during production, transmission (broadcast), storage, and reception. Note: Even digital TV signals are converted to analog to pass through component video or S-video cables and/or just before being displayed on a CRT (picture tube). The fewer analog to digital conversions there are altogether, the better the overall quality can be.
Digital Video Recorder -- Refers to a video recording device that stores the recorded programs in digital form on a magnetic disk such as a computer hard drive.
Diplexer -- Multiplexer (q.v.) which handles two groups of video or other signals.
DILA (Direct drive Light Amplifier) -- JVC's version of liquid crystal on silicon, or LCOS, q.v. video display technology.
Dipolar (as opposed to Bipolar) -- (Speakers) Refers to a speaker system also open in the rear with one relatively flat coned speaker for approximately equal front and rear sound dispersion, or two ordinary speakers facing front and rear, respectively, and wired out of phase. The purpose is to give a more even surround sound effect where the listener is less able to identify the sound as coming from specific speaker's locations. This effect is better achieved in a room with at least a reasonable amount of sound reflection off of the walls. Without such sound reflection, the out of phase acoustic energy from the rear of the speaker system will cancel that from the front depending on where the listener is seated, and unnatural effects may be heard.
Direct View -- Refers to a TV set (or video display device) where the viewing screen is the face of the cathode ray tube or other surface upon which the image is generated. In recent years, non-CRT direct view TV sets, namely with LCD panels and panels with tiny LEDs for individual pixels, have become popular.
Disk, Disc -- We use both words interchangeably, indiscriminately, to refer to any thin flat circular object.
Dispersion -- A measure of over how wide an area a speaker directs its audio output. Generally the higher the frequency the less the dispersion by a given speaker.
Display Device -- A general term to encompass equipment such as TV sets, video projectors, computer monitors, etc. which contain electronic circuitry and which take video signals and produce the final viewable picture.
Display Element -- The component such as an LCD panel (of any size) or a picture tube (CRT) (of any size) that takes a (n electronic) signal representing video and produces an actual picture in visible form which picture may or may not require magnification using additional optical components.
Dithering -- (1) Representing a solid patch of one color shade (or shade of gray) using small juxtaposed dots (or adjacent pixels) of slightly different color shades. Often done when it is not possible to produce the exact color shade desired (2) Noise in a video signal producing an effect that resembles dithering as described immediately preceding. Temporal Dithering -- Varying the color and/or luminance of each pixel slightly from one video frame to the next.
DIVX -- (1) Digital Video Express, a now obsolete video disk technology consisting of disks the same size as and similar to DVDs but with encryption requiring the use of a player that periodically transmitted usage data via telephone line to a video rental service. Disks when purchased (return not necessary) came with a rental period that the purchaser could commence at any time. Simply playing the disk later invoked additional rental periods, or the purchaser could order unlimited viewing for a flat fee. As of 2004 the rental service was out of business and no correctly operating players can play DIVX disks; the players will play standard DVDs. (2) DivX, a coding and encoding system by DivX, Inc., formerly DivXNetworks, Inc. that compresses video into small data files.
DIY -- Do It Yourself.
DLED -- Direct Light Emitting Diode -- A new name for the original LED TV technology where LEDs provide a (at first) uniformly lit panel as a back light and nearly microscopic liquid crystal pixels form a dynamic stencil to produce the image.
DLP; Digital Light Processing -- Texas Instruments, Inc.'s trademarks for its digital micromirror device (q.v.) display elements and technology.
DMD -- Digital Micromirror Device, aka DLP(TM).
Dolby -- A company that manufactures noise reduction circuitry for recording. Also refers to said technology which roughly consists of boosting high frequencies during recording and attenuating the high frequencies (together with any hiss) during playback. The technology is temporal, that is, the amount of boost varies with the amount of high frequency content. There are different versions, Dolby-A usually used by professionals, Dolby-B and Dolby-C, the latter with more noise reduction, used in consumer grade equipment.
Dolby Digital -- One of the formats for encoding surround sound such as for DVD, up to six sound channels including one for a subwoofer. Previously just two sound channels, left front and right front, were provided.
Dolby Vision -- One of the formats for encoding video taking advantage of High Dynamic Range and enhancing highlights and shadow detail. Some encoding is done prior to broadcasting or recording on DVD and decoding is done by the TV set.
D1 -- A standard definition video format with 720 pixels across and 480 pixels high. Originally used for video production prior to the advent of DVD and higher resolution formats.
Dongle -- As used here, a small electronic gadget, typically the size of an audio cassette but which could be larger or smaller, that must be connected between two electronic components such as a DVD player and a TV for processing or converting the signal, where one might have expected just a cable with appropriate plugs to be sufficient. Examples: (1) The 300 to 75 ohm transformer needed between a twin lead antenna cable terminating in two spade lugs and a TV's coaxial antenna jack, (2) (stretching the definition) A transcoder needed to convert component video from a DVD player into RGB to go into a VGA jack of a video monitor.
Dot Crawl -- see Cross Luminance.
Dot Pitch -- The (center to center) spacing between phosphor dots or stripes of the same color on a TV screen. If larger than one pixel then the smaller the better for picture sharpness, 0.28 mm is considered the minimum acceptable for a good CRT computer display, while a typical 20" CRT TV had an 0.81 mm dot pitch and large screen TVs had dot pitches a bit larger. Unfortunately, small (5 to 9 inch) CRT TV sets had dot pitches well in excess of the now easily manufactured .28 mm which made these products have unnecessarily coarse picture quality. Many TV screens use vertical stripes rather than dots in which case the dot pitch applies only in the horizontal direction. Digital displays such as plasma or LCD also have dot pitches which, when equal to the pixel size, do not introduce distortion or cause loss of resolution.
Doubler -- See Line Doubler, or click here for a more detailed description.
Downconversion -- (1) The reconstruction of a video frame or image to have a smaller number of scan lines or pixels. This must be done to put an HDTV picture on a standard definition TV set. See Sampling. (2) Transposition of a block of frequencies, typically one or more programs modulated on carrier frequencies, onto a block of lower frequencies. For example a VCR does a downconversion when it tunes in, say, channel 56 and sends it to the TV as channel 4. (3) (Colloquial) The construction of S-video from RGB or component video or the construction of composite video from S-video. Some experts contend that these last few examples are upconversions since composite video is a more complex format than component video or RGB.
Driver -- A "loudspeaker" in the sense of consisting of frame, cone or other shape diaphragm, and voice coil and magnet or electrostatic grid to convert an electrical signal into vibrating motion, or a similar voice coil and magnet and diaphragm assembly used for audio and not including a required horn or resonating chamber attached to it to deliver meaningful audible output. (2) A computer program that manages an input/output device such as a disk drive or a printer.
Dropout -- Momentary loss of audio or video most often encountered in magnetic tape or magnetic disk recording and playback. Causes include loss of contact between magenetic tape and the tape head, perhaps due to dirt or dust or imperfections in the magnetic coating on the tape or disk.
DTV -- Digital Television; Digital TV, q.v.
DVB (as in DVB-c or DVB-t) -- A digital video encoding standard for (terrestrial) broadcasting (-t) or cable TV (-c) used a lot in the parts of the world that use PAL. Some of the compression techniques include combining (by weaving) odd and even interlaced fields and then performing video compression. The result sometimes resembles 24 fps (sped up to 25 fps) film source video with 2-2 pulldown. The significance is that de-interlacers that recognize 2-2 pulldown produce less than ideal picture quality when the small percentage of the picture material that differs from field to field is processed. Said correct differences often show up as areas of woven even and odd scan lines non-matching in terms of content, referred to as combing.
DVD (originally "Digital Video Disk", now "Digital Versatile Disk") -- A 5" plastic disk that looks like an audio compact disk or compact disk used for data, using the same concept of microscopic pits arranged in a spiral and read using a laser. Except for double sided DVDs (CDs come only single sided) the only way to tell the difference from a CD is to look at the label or markings engraved near the center. Today's DVD's can play a movie just over four hours in length without the need to stop the player and turn the disk over. The present standard (SDTV) DVD picture is usually 704 or 720 (occasionally 640) pixels across by 480 pixels high (576 pixels high for PAL). Live video is stored (recorded) as interlaced, up to 60 fields per second. Film source video may be stored as progressive, up to 30 frames per second. A CD player cannot play a DVD whereas most DVD players can play CD's. For computer use, the nominal capacity of a DVD is 4.7 gigabytes per layer. DVD's may have one or two layers per side, and double layer disks may also be double sided.
DVDO -- Trademark of Anchor Bay Technologies, which produced the the iScan line of de-interlacers. The original DVDO, Inc. was acquired by Silicon Image Corp ca. 2001. In 2003 Silicon Image sold the DVDO and iScan names and the related stand alone de-interlacer business but not the chipset ownership to Anchor Bay Technologies. The latter was a new company some of whose founders founded the original DVDO, Inc. and have since developed new HDTV and SDTV de-interlacing technologies.
DVI (for Digital Video Interface) -- A set of digital video standards for transmitting video between components over wires such as between DVD player and TV set at distances generally up to about 30 feet. Its standards handle all of the common NTSC based SDTV formats and the U.S. ATSC formats and most of the common PC resolutions. HDCP copy protection is also supported. It uses a 24 conductor plug and jack set just over one inch by 1/4 inch in size. The transmission itself is over either a single 12 wire (single link) or two 12 wire (dual link) 165 MHz data channel(s).
DVLED -- Direct View Light Emitting Diode -- The (directly viewed) image uses LEDs (clusters of 3 LEDs for red, green, blue) for individually illuminated pixels to produce the image without the use of LCD crystals or a back light. This is a refinement of the OLED technology where more durable and not necessarily organic materials have been developed to make the LED elements or pixels. DVLED and Micro LED are somewhat the same technology where, in 2023, DVLED has referred to commercial displays (over 100 inches diagonally) and pixel sizes typically more than 2 mm.
DVR -- Digital Video Recorder; a device that records video (e.g. TV programs) onto a hard drive or other digital storage media.
Dynamic Range -- Ratio of the loudest and softest sounds that an audio system can reproduce or the ratio of the brightest and darkest shades (contrast ratio) that film or a video system can reproduce.
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