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Audio and Video Definitions (Part One of Four)

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badababa avatar
Posted: Wed Feb 09, 2011 09:01
Audio and Video Definitions (Part One of Four)

Audio and Video Definitions

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 that require a power source to perform the desired function. A switcher that has remote control capability is alwa
ys 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 different 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 ™, 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.

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.

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. high definition 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 60 frames per second (progressive 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. see AFC.

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.

Glossary B

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 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. 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".

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.

Beaming -- A tendency of a speaker to direct its output narrowly, in one direction. When 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 wires 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 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) opaquecoating 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.

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.

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 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".)

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 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 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.

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; if the recorded content is no longer wanted, additional material can be recorded only on the space remaining subject to the recording method chosen, or if there is no remaining space the disk is discarded. The disks themselves are constructed differently from ordinary non-recordable CD's. Ordinary CD's are stamped like grooved records, and then the silver or gold reflective layer applied. Recordable CD's have the foil layer (gold colored) already applied, and the recording consists of "burning" the pits into an intervening layer of organic dye one at a time. "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.

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".

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 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.

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, ( one amplifying element (such as a tube or transistor) can reproduce the entire signal (waveform) without significant distortion, and © 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 toAC. 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, ( 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, © 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.

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 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 (red to cyan content, white to black content, and 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.

Coloration -- Any distortion occuring 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 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 DVD's.

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 CRT's 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 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 -- Not to be confused with Composite video. In current usage, refers to analog component video , q.v. More generally, a video signal transmitted as at least three separate components (subsignals) using separate wires or cables. 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 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 a 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 systems NTSC, PAL, and SECAM has its own definition of how the luminance and color are combined. 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 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. 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.

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.

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) 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.

Convergence -- (1) The correct aiming of the three electron beams in a direct viewed picture tube or three separate pictures from 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 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 CRT's 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.

CRT -- Cathode Ray Tube.

CUE -- See Chroma Upsampling Error.

CVBS -- Composite video.

Glossary D

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.

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 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. Currently (2005) due to the cost of DMD display elements, a TV using this technology typically has only one of them 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 to flash sub-images of the 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 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 some 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 has 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, 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 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 speakers 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 LCD panel and plasma sets, 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 (usually a small number 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 DVD's 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 DVD's. (2) DivX, a coding and encoding system by DivX, Inc., formerly DivXNetworks, Inc. that compresses video into small data files.

DIY -- Do It Yourself.

DLP; Digital Light Processing -- Texas Instruments, Inc.'s trademarks for its digital micromirror device display elements and technology.

DMD -- Digital Micromirror Device, aka DLP™.

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.

Cont. on part 2 of 4

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