Glossary Terms

Provided by Joe Kane and Stewart Filmscreen.

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ACC (Automatic Color Correction) A circuit found in many consumer viewing devices that attempts to compensate for the "Never Twice the Same Color" problems that have been found in broadcast quality. Depending on the implementation, this type of circuit can go far beyond the Auto Tint function. It changes color saturation as well as type of color. In most cases, where an ACC circuit is present, it can not be turned off. Adjusting the color and tint controls, using the SMPTE Color Bar pattern and the blue filter will result in a gross misadjustment of color level on the set. The color level may have to be reduced by as much as half the value calibrated with the SMPTE Color Bar pattern. VE T12 C1, VE T13 C3-5

AES (Audio Engineering Society) The Audio Engineering Society is the only professional society devoted exclusively to audio technology. The AES serves its members, the industry and the public by stimulating and facilitating advances in the field of audio. It encourages and disseminates new developments through annual technical meetings and exhibitions of professional equipment, and through the Journal of the Audio Engineering Society, the professional archival publication in the audio industry.

AFC (Automatic Frequency Control) A circuit that automatically keeps an oscillator on frequency. When present on a TV set, the AFC control usually applies to the TV channel tuning section. It keeps the tuner locked to the channel selected. It could also be labeled AFT for Automatic Fine Tuning. Modern sets with digital tuning often have this capability built in, without an option to turn it on or off. Under normal circumstances this function is desirable and should be left on. An ability to turn it off might be helpful when the TV set is using an antenna to receive distance signals in the face of strong local signals. The function of AFC can be applied to other circuits in a viewing device. In those cases we挿�ve not seen an ability to turn the AFC on or off. If it exists it is always on.

AGC (Automatic Gain Control) Automatic gain can be applied ahead of almost any circuit that requires specific levels to operate. As an example, the color decoder needs to see a particular level of color subcarrier at its input in order to display the correct color at the output. There is a reference burst of color subcarrier at the beginning of each horizontal line of known original amplitude. The AGC circuit looks at the incoming signal level and applies what ever gain correction necessary to make that burst correct in amplitude. In the process of doing that, it also corrects the amplitude of the color information in the active picture area. There are certain limits in the accuracy of this circuit. If the incoming burst amplitude is really low, the AGC circuit might not function at all or amplify the signal more than it should. This is of particular concern when attenuation in the cable delivering the video signal to the set reduces the color information much more than it should. The AGC circuit will actually cause the color to look high, if it has over amplified the weak signal, or the set may only display a black and white picture if it doesn挿�t amplify the signal at all. Several S-Video cable manufacturers have been know to play this game, claiming their cable delivers richer color quality.

Ambient Light: All light in a viewing room produced by sources other than that of the projector and the screen.

Analog (Analogue) A continuous signal that requires time to make a transition from one level to another. Standard audio and video signals are analog. Both can be digitized. The video in the laserdisc format is analog composite. The audio can be present in both analog and digital forms. Both the audio and video on DVD has been recorded on the disc in the digital domain. The alternate, British spelling of the word analogue is often used in the audio world.

Anamorphic Video Found on a large number of DVD's, anamorphic video appears to squeeze a 1.78 picture shape into a 1.33 image area. If you view an anamorphic video image on a 1.33 set, the characters will look tall and thin. In reality the active video area has been redefined as a 1.78:1 aspect ratio, as the high definition video active area is 1.78:1. This format is designed for 1.78 aspect ratio TV sets. This approach offers about 33% more vertical resolution to widescreen images. Unsqueezing an anamorphic image on a 1.33 set is accomplished by squeezing the vertical size. Back in the mid-90挿�s Toshiba released four laserdisc titles as promotional material in anamorphic video, prior to the coming of DVD. The four titles are "Free Willy", "The Fugitive", "Grumpy Old Men" and "Unforgiven".

ANSI (American National Standards Institute) From their web site "The American National Standards Institute (ANSI) has served in its capacity as administrator and coordinator of the United States private sector voluntary standardization system for more than 80 years. Founded in 1918 by five engineering societies and three government agencies, the Institute remains a private, nonprofit membership organization supported by a diverse constituency of private and public sector organizations.

Throughout its history, the ANSI Federation has maintained as its primary goal the enhancement of global competitiveness of U.S. business and the American quality of life by promoting and facilitating voluntary consensus standards and conformity assessment systems and promoting their integrity. The Institute represents the interests of its nearly 1,000 company, organization, government agency, institutional and international members through its office in New York City, and its headquarter in Washington, D.C.

ANSI does not itself develop American National Standards (ANSs); rather it facilitates development by establishing consensus among qualified groups. The Institute ensures that its guiding principles -- consensus, due process and openness -- are followed by the more than 175 distinct entities currently accredited under one of the Federation挿�s three methods of accreditation (organization, committee or canvass). In 1999 alone the number of American National Standards increased by nearly 5.5% to a new total of 14,650 approved ANS. ANSI-accredited developers are committed to supporting the development of national and, in many cases international standards, addressing the critical trends of technological innovation, marketplace globalization and regulatory reform."

APL (Average Picture Level) The video signal level, during the active picture part of each horizontal line, is mathematically averaged over the period of a frame to come up with APL. A 100 IRE Window pattern has a lower APL than a 100 IRE Flat Field pattern. Television program material is said to have a 15% average picture level over a long period of time. The Window patterns used for setting gray scale in all three titles have a 16% APL so that they will closely represent normal program material in their current drain on the high voltage power supply. The width of the Window was enlarged the extra 1% to accommodate the shape of the Philips PM5539 Color Analyzer which was on the market at the time of A Video Standard. That wide aspect ratio shape was passed on to Video Essentials. The computer world uses a much higher number for APL over time, that of 35%. That is reflected in the ANSI Checkerboard Patterns, VE T17 C27.

Aperture Correction As applied to a video signal, this is frequency peaking, usually at just one frequency, to compensate for loss of picture detail. Aperture correction is applied in the video camera. The sharpness control, in the display device, serves a similar frequency compensation function. There are times when the terms "sharpness" and "aperture correction" are used interchangeably. See VE T14 C1-5.

Aspect Ratio defines the shape of the rectangular picture in a TV set. It is the width of the picture relative to the height. Our standard TV picture, in terminology used by that industry, is 4 units wide by 3 units high, or 4:3 (read as 4 by 3) in aspect ratio.

There is more than one way to express an aspect ratio. In film terms the width of the screen is 1.33 times the height. Divide 4 by 3 and you get 1.33333... It has an aspect ratio of 1.33:1 (read as 1.33 to 1). Since the :1 is always the same it is often dropped for the definition. We then say that the set has a 1.33 aspect ratio instead of saying it has a 1.33:1 aspect ratio. This is an easy system to use in that the larger the number the wider the set. A 1.78 set is wider in aspect ratio than a 1.33 set.

Of the two numbering systems, you might initially think it's easier to use the 4:3 instead of 1.33:1 or just plain 1.33. That works until you get to multiple aspect ratios. Then it becomes difficult to determine what the numbers are telling you about the shape of the picture. Picking on two widescreen sets that have been available in the U.S., which is wider, one that is 16:9 or one that is 16:10.5? Asking the same question in decimal systems makes it much easier to answer that question. Which is wider, 1.78:1 or 1.52:1? The decimal system makes it much easier to determine the correct answer. 1.78 is wider than 1.52. Since there are a number of aspect ratios currently in use, not all of which can be expressed as whole numbers, the decimal system is by far the better choice.

The film community has many more aspect ratios and has therefore adapted the decimal system to describe the shape of the picture.

There are currently two standard TV aspect ratios in the U.S., 1.33 (4:3) and 1.78 (16:9). The 1.52 aspect ratio set is sort of a compromise in the transition from one system to another. They alter picture geometry to get either 1.33 or 1.78 to show up on the 1.52 screen. In the DTV world we挿�ll see a bit of 1.55 or 14:9 as another option in the compromise. That挿�s what will be done to 1.33 images as they are upconverted to a raster that is defined as 1.78. Some of the top and bottom of the 1.33 image will be cut off so that the image can appear to be wider on the 1.78 set. There will still be slight black bars on the left and right edges of the image.

Several manufacturers are advocating 1.90 because it's a common aspect ratio for many American movies. The Director's Guild has called for a study of making 2:1 the shape of new video displays. It is also possible that some day the high definition active picture area will be redefined as 2.35 from its current 1.78 aspect ratio. This is just another extension of defining the 1.33 aspect ratio of standard definition television to 1.78 in the DVD format.

If the future of television is widescreen, is one aspect ratio better than another? Knowing that we will have to accommodate the 1.33 aspect ratio for some time to come, the question becomes how wide can we go and still deal with the 1.33 image in the center? The resolution of current display technology would suggest that 1.78 is the upper limit of our current capability. The 1.33 image is compromised by only being able to use the resolution in the center of the display and images wider than 1.78 can挿�t use the resolution available at the top and bottom of the display. Some of these problems can be partially resolved by the use of high quality scalers and displays that far exceed the resolution of the source signal. That gets tough to accomplish as the resolution of our source signals goes up. It looks as if the 1.78 imager has a long life ahead of it as a compromise between 1.33 and all of the wider aspect ratio pictures.

ATSC (Advanced Television Systems Committee) From their web site "The Advanced Television Systems Committee (ATSC) is an international organization of 200 members that is establishing voluntary technical standards for advanced television systems. ATSC Digital TV Standards include digital high definition television (HDTV), standard definition television (SDTV), data broadcasting, multichannel surround-sound audio, and Satellite direct-to-home broadcasting.

As detailed in the "Development of the ATSC Digital Television Standard," on December 24, 1996, the United States Federal Communications Commission (FCC) adopted the major elements of the ATSC Digital Television Standard (A/53) for the nation's next generation of broadcast television. In addition, Canada, S. Korea, Taiwan and Argentina have adopted the ATSC DTV Standard for digital terrestrial broadcasts.

ATTC (Advanced Television Technology Center) This is a private, non-profit corporation organized by members of the television broadcasting and consumer products industries to test and recommend solutions for delivery and reception of a new U.S. terrestrial transmission system for digital television (DTV) service, including high definition television (HDTV). The Technology Center operates a state-of-the-art laboratory facility that supports the needs of the U.S. television industry and private standards-setting bodies. Its primary activity is to facilitate implementation of digital television.

Automatic Picture Stop (Noted as PS in the LD index for Video Essentials. There are also automatic picture stops in A Video Standard.) The laserdisc player will automatically take the program from the play mode to a still frame mode according to information programmed in the vertical interval of the disc's video. The Pioneer VP-1000 consumer videodisc player requires the frame display to be on before the automatic picture stop function can be activated. Early VP-1000's required the "Play" button and some other control button, including "Play", to be pressed prior to activating the frame display before the Auto-Picture Stop function would work. (Press "PLAY" twice then the Frame Display. The disc would then stop at all Auto-Stop codes as long as the Frame display remained on.)

The DVD has a similar capability. A pause is written into the program running the DVD at the point where the program should be halted. The pause can be timed and/or require a command from the viewer to move on in the program. Examples of that can be found in many places in Video Essentials. It first shows up at the end of Chapter 5 in Title 1. It happens often in Titles 10 through 14.

Bandwidth A range or band of frequencies. Bandwidth often implies consistency of other parameters, such as amplitude or phase, in addition to defining the frequency range. In reality, a specification for bandwidth is meaningless without additional qualifying information.

Baseband Video and audio signals are considered to be "prime", or baseband. Video and audio can be broken down into more basic elements, but those elements no longer constitute the desired signal as a single element. Baseband video and audio signals are often AM or FM modulated onto a carrier frequency, so that more than one set of "prime" signals can be transmitted or recorded at the same time.

Black Drop: Screen material that is painted black and located between the image and the bottom of the case. Luxus Model A, SR-1, and SR-A come with a standard of 12". Communicator comes with a 3" black drop. All of Stewart's screens have black drop if they are wrapped around a roller. If black drop is not used and left wrapped around a roller tube it can cause wrinkles in a screen. 

Black & White Monochrome or luminance information. Monochrome means one color. In the color television system the Black & White portion of the picture has to be one "color"; gray, D6500, 6500曳�K as defined by x and y values in the 1931 CIE color coordinate system. The black and white signal in the S or Component video path is separate from the color information.

Black Level, strictly interpreted, denotes the light level at which a video signal representing picture black is reproduced on your TV screen. You probably already know that in terms of light output from a TV set black areas of the picture should be represented by an absence of light. Something that is black or below black in the video signal shouldn't produce any visible light from the display. VE T9-11.

Some TV sets actually use Black Level as a control name. It is a far better description of the function of that control than the most commonly found name for it, which is Brightness.

The multiple use of the term black level in the real world comes in the number of variables that affect the way you see light. Among them is the set's ability to produce an absence of light. How dark is it in the "off" state? VE T1 C5.

Black level also becomes a rather large problem when implementing light valve technology. It is difficult to shut light completely off in a small area of the picture.

Light output, from a standard direct view TV is obtained by lighting up phosphors. If you want to produce something representing black, just don't turn on the phosphors in that area of the picture. Simple enough, right? Well no, it isn't actually that easy. If ambient light is hitting the surface of the set, the level of light required for a dark area of the picture will have to compete with that ambient light. The appearance of the "off state" of the phosphors is of course dependent on ambient light. If you were around in the early days of black and white TV you may remember that TV sets had a medium cream color when the set was off. The only way you could get a good black out of a B&W set was to keep all ambient light off the surface of the set. Black matrix picture tubes have been designed to assist with these problems in color TV's. Even black and white sets now have tinted glass fronts in order to reduce the effect of ambient light. This increases the apparent contrast of the picture. These changes in the surface condition of the set increase the apparent contrast when confronted with ambient light.

Ambient light rejection is a great idea for most of us, but it comes at a price. If you can attenuate light hitting the set, you'll probably also attenuate light (picture) information coming from the set. The most obvious example of the price you pay comes in the many sets that put a dark piece of glass in front of the picture tube. This is essentially the same technique used in current B&W sets except that the tinted glass in an integral part of the B&W picture tube. You can't get rid of it.

Picking on a set that we've measured, the piece of glass in front of the set attenuated ambient light by 60% as it passed through the glass on its way to the picture tube. The black matrix in the picture tube itself took the remainder of the incoming ambient light down by an estimated 80% over what we believe an early B&W set would have done. This leaves about 8% of the light to be attenuated again by another pass back through the glass to the viewer. In other words, ignoring the reflections of the polished glass surface, more than 95% of the ambient light hitting the set is absorbed by the set. The cost? At least 60% of the light output capability of the picture tube. The attenuation of the glass was the same in both directions. The picture tube had to be driven well into blooming in order to get a usable amount of light in a well-controlled environment. The quality of the picture was dramatically improved by removing the glass on the front of the set.

Obtaining a good black level from a front screen projection system is even more difficult. Most screens are designed to reflect light back to the viewer, all light including ambient light. There are screens on the market that will attenuate ambient light that is coming in from side angles, but, as with the same thing in a TV set, it comes at a price of picture quality.

Tight control over ambient light is the best way to obtain a good black level from most display devices. Much of the rest of the story about black level is spread out over several other terms. VE T1 C5.

Blooming occurs when you drive the phosphors harder than they should be driven. Phosphors can only take so much energy from the electron beam. The amount of energy they can take is partially limited by their ability to dissipate heat. In a black and white set, where the phosphors are continuous, heat dissipation is better than in a color set where phosphors are tiny, isolated areas; stripes in the case of most consumers TV sets, small dots in the case of many high resolution computer monitors. In CRT based projectors, phosphors are liquid cooled to increase their light output capability.

When phosphors are driven harder than they should be, they disperse much of the extra energy to adjacent areas. It's sort of like sharing the load. The problem with sharing the load is that areas of the picture that shouldn't be lit up are lit up. That reduces the sets ability to show fine detail, not to mention slight light output changes near peak white.

Blooming causes a softening of edges, a lack of gray scale detail near white, and often a change in color quality. Keeping a set out of blooming is therefore important to a good picture. Doing that requires turning the Contrast control way down. Since most sets come from the factory with the Contrast control turned all the way up, it will often be difficult for you to judge the real capability of a TV set when viewed in the store.

An important consideration in purchasing a set is, will it produce a usable amount of light once the Contrast is turned down below the point of blooming. VE T11.

Liquid cooling the phosphors introduces its own set of problems. In the case of CRT based projectors, the phosphors can be driven hard enough to decay in their light output capability. Light output capability from a device being driven this hard will often drop by as much as 50% in the first 1,000 to 2,000 hours of use. It will usually not drop much below the 50% point once it gets there as long as you don't drive the set into blooming. If you do overdrive the set, count on it burning the phosphors. I've encountered a number of circumstances where the tubes have to be replaced in as little as 800 hours, as opposed to the 10,000 hours that they should have lasted.

It's possible to burn an ordinary TV set. Video games in particular have fixed patterns that will burn a set. Cable channels with fixed logos are also a potential source of burns. The most common is CNN. It is not unusual for me to see CNN Live burned into someone's set, all because they didn't turn the Contrast control down below the point of blooming.

When you purchase a TV set, try not to take something off the showroom floor. The high contrast levels displayed at the store can shorten the useful life of the set. When you get your new set home, turn down the Contrast control first thing, then go through Video Essentials to set it up properly. VE T9-11.

Brightness is another term that has a double meaning. When talking about control functions on the TV set, Brightness is used to set the black level of the picture. The original intention of the control term, which seems to have been lost somewhere between the first and second half of this century, was that the Brightness control would set the overall brightness of the picture, adjust the set's ability to compete with ambient light. In reality, what the Brightness control is doing is adjusting the viewed level of black. VE T10.

Brightness is more often used to describe the light output capability of the set. Just keep in mind that the reality of a good picture is actually rather dim. That should help you remember that the Brightness control adjust the black level of the picture. If you want a high quality, bright picture, be prepared to spend lots of money, especially if want it large. How much money? I just helped with the adjustment of a video system on a ten foot wide screen. There was over $65,000. in electronics required to obtain an image bright enough to compete with what you should see in a movie theatre. Certainly not enough output to compete with any ambient light in the room.

CATV (Community Antenna Television), Cable TV. In its early form cable television was an antenna system that served a community.

CCIR International Radio Consultative Committee, was a global organization responsible for establishing television standards. CCIR 601 was the standard for transmitting Digital Video Component information that is recorded by the D1 machine. The CCIR has now become the ITU.

CE (Consumer Electronics) This is often used in association with an industry organization of consumer electronic manufacturers. See the CEA below. It can also refer to the consumer electronics industry in general.

CEA (Consumer Electronics Association) This is an association of consumer electronics manufacturers primarily involved in a general promotion of that industry. The CEA holds an annual convention in Las Vegas each January called the Consumer Electronics Show. The organization is also involved in defining some standards and practice rules for products.

CEDIA (Custom Engineering & Design Installation Association) An international trade association of companies and people specializing in planning and installing electronic systems for the home - typically media rooms, single or multi-room entertainment systems, home automation and communication systems, and integrated whole-house subsystems providing control of lighting, security and HVAC systems. The association was founded in September of 1989.

CES (Consumer Electronics Show) An annual convention held in Las Vegas each January that promotes the industry and its products.

Chapter A chapter in a videodisc is a section divider. Chapters are sub-sets of the videodisc. In the DVD format a chapter is a division of a title.

Character Generator The device used to generate words and numbers in a video format. The characters are subsequently "keyed" over program video or background video.

Chip Chart Black and white test chart. It contains "chips" in varying intensities that make up a gray scale. It is used to check the gray scale taking characteristics of a camera, including the parameter of gamma.

Chroma The characteristics of color information, independent of luminance intensity. Hue and saturation are qualities of chroma. Black, gray, and white objects do not have chroma characteristics.

Chrominance The amount of color; or the saturation of color, in a picture.

CIE (Commission Internationale de l'Eclairage) The International Commission on Illumination. It is the international organization that is responsible for establishing the chromaticity diagram of 1931. The three dimensional 1931 CIE diagram attempts to define light and color. Only two of the three dimensions are represented in this program. There have been several important systems developed by the CIE since 1931. We sort of skip the chart developed in 1969 and go directly to the one put forth in 1976. CIELUV units come from that representation. While the 1976 chart more accurately represents the way we see light, the tradition of using the numbers in the 1931 system still continues. Both systems are represented on this web site.

CODEC (EnCOder/DECoder) A process or device by which or in which a signal is encoded for transmission or storage, then decoded for playback. As a process it is the algorithm that handles the compression and decompression of video or audio files. As a device it could be a box or computer card that accomplishes the encode/decode process.

COFDM (Coded Orthogonal Frequency Division Multiplexing) A method by which digital information is encoded for transmission. Bell Labs developed it here in the United States. This particular system of encoding has been chosen by the European community for their terrestrial transmission of digital television. The system can be used for transmission of any kind of data within the limitations of the maximum bit rate of the system. The specification only describes the transmitted signal and thus does not specify receivers. The data container is an MPEG-2 transport stream.

COFDM versus 8-VSB The requirements of modulation for digital TV are significantly different from that of a single carrier QPSK modulation specification for satellite and single carrier QAM modulation for cable. The terrestrial channel may be impaired by severe multipath, due to terrain and buildings, electrical noise, environmental conditions, and the congested frequency spectrum. The Europeans have chosen COFDM. The US has chosen 8-VSB.

Color Difference Signals These signals can evolve in the processing of encoding or decoding between RGB and composite video. They occur in pairs and are forms of R - Y and B - Y. I and Q are the band limited, reduced amplitude color difference signals used in transmitting color information in NTSC. Most of the component video systems now handle three video channels: Y, R - Y, & B - Y. The D1 digital recorder stores the digital equivalent of luminance and the pair of color difference signals.

There are any number of designations for component video. In the digital domain, the SMPTE spelled out component as Y C_b C_r. Even the order has changed from Y R-Y B-Y where C_b represents B-Y and C_r represents R-Y. The designation has since evolved to Y P_b P_r. While this designation is most often associated with an analog signal, we挿�ve seen it applied to the digital world.

Color Subcarrier The frequency that carries the color information in the baseband composite video signal. In NTSC the color subcarrier is 3,579,545 Hz, 路� 10 Hertz. This number is usually rounded off in text to 3.58 MHz.

Unlike the black and white television standard, where the vertical and horizontal frequencies are derived from the 60 Hz power line frequency, the color subcarrier became the clock reference for the color system. The horizontal and vertical frequencies are now derived from the color subcarrier rather than the power line rate. When we shifted to the color system in 1954 the horizontal and vertical rates changed. The amount of change was small enough so that black and white sets would still synchronize to the updated rate.

A color sync burst of 3.58 MHz is added to the beginning of the horizontal lines to synchronize the color decoding circuits in the display device with the source video.

The phase of the color information in the video is changed 180曳� for every adjacent line. The change occurs automatically as part of the horizontal timing being derived from the color subcarrier. It has the overall effect of canceling the display of the color subcarrier in the picture. It does, however, produce "dot crawl" at color transitions.

It takes two complete pictures for the phase relationship between the subcarrier and horizontal signal to return to zero. (This presents a minor problem for laserdisc players when displaying a still frame. The color phase has to be electronically reversed every other time a single frame is repeated because a still frame is only half of a color cycle.)

See Horizontal Scanning Frequency and Vertical Scanning Frequency below to see how they are derived from the color subcarrier.

Component Video In producing a color picture from light, our color television system starts out with three channels of information; Red, Green, & Blue (RGB). This is certainly one form of component video. In the process of translating these channels for use in distribution, they are often first converted to Y, R-Y, and B-Y or Y P_b P_r. This is another form of component video. The term component describes a number of elements that are needed to make up the picture. It could be argued that an S video signal is also a component signal. A composite video signal on the other had contains all the information needed for the color picture in a single channel of information. Much higher program production quality is possible in the component domain because analog compression is used to place the three channels of component information into the single channel of composite information. Once that compression take place it is extremely difficult to get back the original quality of the component signal.

One of the advantages DVD has over the laserdisc format is that it is component based.

Composite Video A single video signal that contains luminance, color, and synchronization information. NTSC, PAL, and SECAM are all examples of composite video systems.

Contrast can refer to the control used to set the peak white level of the picture or the ability of the set to show a large difference between black level and white level. A high contrast picture will usually look as if there is much more detail in it.

Contrast Ratio is the difference between the dark part of the picture and the light area of the picture. It is calculated by dividing the peak white level by the light level at the dark park of the picture. Measurements are taken by displaying a 100% Window pattern and measuring the peak white and an area of black near the white rectangle. The contrast ratio of a picture can be enhanced much faster by obtaining a good black level than by increasing the white. If we could actually get black to go to zero the contrast ratio would go to infinity. You would have to go a blinding way in peak light output to otherwise reach anywhere near that number.

The contrast ratio of a good black matrix TV set in reasonable ambient light conditions is about 50:1 Get rid of ambient light hitting the set altogether and the number is more in the order of 100:1. The contrast of a direct view TV set appears to be pretty good because of its ability to reject ambient light. Broadcast grade monitors, which do not have the black matrix "feature", are often hard pressed to reach contrast ratio numbers much higher than 100:1. On the other side of this coin, the average viewer at home doesn't see numbers any higher than 50:1, often being as low as 10 or 20:1 depending on how well black level is set and held by the TV set.

It is even more difficult to get a good contrast ratio out of a two piece projection system. Lower peak white capability and less ability to reject ambient light can often lead to a picture that doesn't look as high in contrast as a good TV set.

CRT (Cathode Ray Tube) A vacuum tube that produces light when energized by the electron beam generated inside the tube. A CRT has a heater element, cathode, and grids in the neck of the tube, making up the "gun". An electron beam is produced by the gun and is accelerated toward the front display surface of the tube. The display surface contains phosphors that light up when hit by the electron beam. The CRT is more commonly known as a picture tube.

CX Noise Reduction used primarily in the analog audio tracks of laserdiscs. This is a level sensitive audio noise reduction scheme that involves compression, on the encode side, and expansion, on the decode side. It was originally developed for CBS for noise reduction on LP records and is a Trademark of CBS Inc. The noise reduction obtained by CX was to be better than Dolby B3 for tape, but remain unnoticeable in playback if decoding didn't take place. A modified CX system was applied to the analog audio tracks of the laserdisc to compensate for interference between the audio and video carriers. The original CX system for LP records was never commercially implemented. Its implementation in laserdisc is slightly different than was being proposed for LP挿�s. Stand-alone CX decoders were on the market from Pioneer in the early days of laserdisc.

DAB (Digital Audio Broadcast) DAB, as designed for implementation in Europe, is broadcast terrestrially. It is received using a tiny non-directional stub antenna. It provides CD-like quality radio programs without the annoying interference and signal distortion associated with mobile radios. In addition, the system can offer text, pictures, data and even motion video.

DARS (Digital Audio Radio Service) Part of the DAB system.

DAT (Digital Audio Tape) A digital audio tape recording format that uses a primary sampling rate of 48 KHz. It is also capable of directly recording the 44.1 KHz CD digital audio format. Its full name is R-DAT. The "R" describes the rotating head that is used to record the signal. The DAT system is pretty much limited to professional use in the United States. An S-DAT format was also proposed where the tape moved past a stationary head fast enough to properly record digital audio information.

dB (Decibel) The standard unit used to express gain or loss of power along a signal path. It indicates the logarithmic ratio of output power divided by input power. A power loss of 3 dB is an attenuation of the incoming signal by half of its original value. A 3 dB power loss is equal to a 6 dB voltage loss. [dB = 10 log P1/P2, P = V�/R, If R is a fixed value, then: dB = 10 log (V1/V2)� or dB = 20 log V1/V2. ] This method of scaling levels becomes important because human sensitivity to sight and sound are logarithmic, which accounts for our large dynamic range capability.

DBS (Digital Broadcast Satellite) DBS is television service that allow households to receive television programming directly from satellites on 18" inch to 3挿� diameter fixed position satellite dishes. Composite analog video from standard cable services are converted to component digital, then MPEG compressed for transmission. This allows several programs to be broadcast from a single satellite transponder thereby allowing up a large number of channels to be received with a dish pointed at one orbital position in the sky. Programming on the various services includes most major cable services, sports, Pay Per View (PPV) movies, audio services, and specialized "niche" programming aimed at smaller audiences. These are often referred to as Direct To Home (DTH) services but the term Direct Broadcast Satellite (DBS) is more commonly used. HDTV programming is now available on some DBS services.

DC Restoration is the ability of a set to hold black at black independent of picture content. In most sets the level of black floats, it goes up as the picture gets dim in content and goes back down as picture content gets brighter. The idea behind most sets having poor DC restoration is that consumers watch TV in high ambient light conditions. If the scene gets dark, the set pushes up the black so that you won't miss any detail. The problem with bringing black up is that it washes out the contrast of the picture. If you watch a set in well controlled ambient light, the change in black level and subsequent destruction of contrast ratio well make for poor viewing. The idea of DC Restoration is to clamp the back porch of the video signal to 0 Volts DC. (Synchronization signals go below that level and picture information goes above that level. The DC refers to Direct Current as AC refers to Alternating Current.) If you are looking for a high quality TV set, DC restoration should be at least 96%. It is actually difficult to get much above 98%. Even broadcast grade monitors are not perfect. VE T10 C2-10.

Decoder, Video, Composite to Component (See NTSC Decoder) A device that solves the three equations in the composite signal to come up with the component elements, Y P_b P_r or RGB. There are two types of decoders commonly used for NTSC signals, the notch filter or comb filter.

Degauss The process of demagnetizing the CRT. Magnetic fields are used to move the electron beam across the surface of the CRT. Stray magnetic fields can cause the beam to go places it is not supposed to go. Most color sets have automatic degaussing when the set is first turned on. Utility and broadcast grade monitors offer the additional capability of being able to manually degauss the set.

D-ILA� (Direct drive Image Light Amplifier) A JVC lightvalve technology. The ILA is a reflective mode active matrix liquid crystal display, also referred to as LCOS, Liquid Crystal On Single crystal silicon. The back side of the 0.9 inch diagonal liquid crystal is currently being driven by a 1365 by 1024 active matrix CMOS array. The pixel electrodes of the device have a 93% aperture ratio. A detailed description of the technology can be found at http://www.hjt.com/technology/download/DILA2.pdf .

Digital A two state, on or off, signal system. Analog signals can be converted to digital signals. They are sampled at a particular rate. Each sample is converted into a digital "word" that represents the analog value of the signal at that given instant of the sample. A digital word contains many bits of on or off digital information.

DLP� (Digital Light Processing) A Texas Instruments technology for video projection. When the TI engineers unveiled what is now known as the Digital Micromirror Device环�, (DND) they demonstrated a chip with a 16 x 16 display. That chip became the foundation of Digital Light Processing环� technology. After more than 22 years and a myriad of innovations, DLP now displays resolutions up to 1280 x 1024.It is also know as DMD for digital micro-mirror device.

DMD� (Digital Micro-mirror Device) A Texas Instruments technology for video projection. See DLP.

DTCP (Digital Transmission Copy Protection) DTCP Specification is to allow for protected transmission of copy-protected material between digital devices like PC's, DVD Players, and Digital TV's, five companies -- Hitachi, Intel, Matsushita (MEI), Sony and Toshiba have prepared the "5C" Digital Transmission Content Protection (DTCP) specification. The DTCP specification defines a cryptographic protocol for protecting audio/video entertainment content from illegal copying, intercepting and tampering as it traverses high performance digital buses, such as the IEEE 1394 standard. Only legitimate entertainment content delivered to a source device via another approved copy protection system (such as the DVD Content Scrambling System) will be protected by this copy protection system. The DTCP specification relies on strong cryptographic technologies to provide flexible and robust copy protection across digital buses.

DTLA (Digital Licensing Transmission Authority) Administration for DTCP.

DTV (Digital Television) Often used to describe one of the many new forms of terrestrial transmission of video program material.

DVB (Digital Video Broadcasting) The Digital Video Broadcasting Project includes over 220 organizations in more than 30 countries worldwide. Members include broadcasters, manufacturers, network operators and regulatory bodies, committed to designing a global family of standards for the delivery of digital television. Numerous broadcast services using DVB standards are operational in Europe, North and South America, Africa, Asia, and Australia.

DVB systems are developed through consensus in the working groups of the Technical Module. Members of the groups are drawn from the general assembly of the project. Once standards have been published, through ETSI, they are available at a nominal cost for anyone, world-wide. The standards are based on the common MPEG-2 coding system.

DVD (Digital Video Disc or Digital Versatile Disk) A 12 cm optical disc format designed to function as a data storage medium. When fully implemented it has the potential of replacing other optical media such as the laserdisc, audio CD, and CD-ROM. It also has the potential of replacing VHS tape as a distribution format for movies.

DVD Terminology and Frequently Asked Questions: See Jim Taylor挿�s "DVD Demystified".

EBU (European Broadcast Union) The European Broadcasting Union (EBU) is headquartered in Geneva, Switzerland and works on behalf of its European members. The EBU negotiates broadcasting rights for major sports events, operates the Eurovision and Euroradio networks, organizes program exchanges, stimulates and coordinates co- productions, and provides a full range of other operational, commercial, technical, legal and strategic services. At its office in Brussels, the EBU represents the interests of public service broadcasters before the European institutions.

The EBU was founded in February 1950 by the pioneers of radio and television in Western Europe. It merged with the OIRT - the former union of eastern European broadcasters - in 1993. Apart from its active members in Europe, North Africa and the Middle East, the Union has 49 associate members in 30 countries outside of Europe. These include the Asia Pacific Broadcasting Union (ABU), the North American Broadcasters' Association (NABA), the Union of National Radio & Television Organizations of Africa (URTNA), the Arab States Broadcasting Union (ASBU), and the Organizacion de la Television Iberoamericana (OTI).

The Union is involved in radio data system (RDS), digital audio broadcasting (DAB), digital television (DVB), and high- definition TV (HDTV).

EIA (Electronics Industry Alliance) This is a trade alliance for its members who are engaged in or associated in the manufacture and sale or distribution of many categories of electronic equipment.

EPG (Electronic Program Guide) It挿�s initial implementation has been in the cable industry where an on screen guide to television programming is provided. There are now service providers and equipment that have interactive version of a program guide. They allow the user to point at a program, then do something with it such as making sure it is recorded or that the set is turned on and properly tuned at the program comes on.

FCC (Federal Communications Commission) The FCC is an independent federal regulatory agency responsible directly to Congress. Established by the Communications Act of 1934, it is charged with establishing policies to govern interstate and international communications by radio, television, wire, satellite, and cable. Its jurisdiction covers the 50 states and territories, the District of Columbia and U.S. possessions. Five Commissioners direct it. They are each appointed by the President and confirmed by the Senate. They serve staggered five-year terms. No more than three Commissioners can be members of the same political party. The President designates one of the Commissioners to serve as Chairman.

The Chairman presides over all FCC meetings. The Chairman coordinates and organizes the work of the Commission and represents the agency in legislative matters and in relations with other government departments and agencies.

The Commission is committed to the use of emerging technologies to serve its customers -- the American public and regulated industries -- more efficiently. It continues to expand its use of the Internet, which has become an increasingly popular way for the public to access information.

The Mass Media Bureau is the part of the FCC that deals with broadcasting -- television and radio -- as well as Multipoint Distribution Service (MDS) (sometimes called wireless cable) and Instructional Television Fixed Service (ITFS), a service used mainly by educational entities to provide classroom instruction to multiple locations. The Bureau issues licenses (authorization of service), performs policy and rulemaking functions and administers the enforcement program for all mass media services.

Field The picture information in an interlaced video system is divided up into two equal parts, called fields. A field is one-half of a frame or complete video picture. Adjacent lines in a TV picture are located in alternate fields.

Field Dominance When a CAV laserdisc is placed in the still frame mode, it continuously plays back two adjacent fields of information. There are no rules in the NTSC system stating that a complete video picture has to start on field 1 or field 2. Most of the video in this program is field 1 dominant, the picture starts on field 1. There are two sections of the disc that are field 2 dominant. In the case of film translated to video, the start of a complete film picture changes from field 1 to field 2 about 6 times a second. There is a code in the vertical interval of the disc that tells the player on which field it can start displaying each of disc's still frames.

Film Chain A device that transfer a film image to a video image. It is also known as a Telecine chain.

FM (Frequency Modulation) A process of translating baseband information to a higher frequency; carrier frequency, so more information can fit into a transmitted or recorded space. The video and two analog audio channels are FM modulated on to their own carriers so that they will all fit on the disc. The process: The two input signals to an FM modulator are the baseband signal (video or one of two audio channels) and the carrier frequency (a constant amplitude and constant frequency signal). The frequency of the carrier is modulated (changed; increased and decreased about its zero state) by the amplitude of the baseband signal. A large amplitude signal will cause a large shift in the carrier frequency, etc. The rate of shift (how fast the carrier is changed from one frequency to another) is determined by the frequency of the baseband information. The FM system is often preferred to AM (Amplitude Modulation) as a carrier of baseband information because of its greater noise immunity.

Foot Lamberts is a measure of reflected light in a square foot area. A typical 27" consumer TV set will produce about 30 foot Lamberts of light output before going into blooming. A 27" TV set I once owned produced about 187 foot Lamberts in the factory reset mode. It had to be pulled down to about 27 foot Lamberts to get it out of blooming. A well designed two piece home theatre projection system should produce about 10 to 11 foot Lamberts in its linear operating range when it is new. Many 32 to 36 inch sets won't produce much over 15 foot Lamberts in their linear operating condition. High resolution computer monitor are also not capable of much light output if you want to take advantage of their real resolution capability.

Frame In film or video, a frame is a complete picture. In interlaced NTSC video a frame consists of two fields. In a videodisc, the word frame refers to a single picture. It can mean film picture or video picture.

Fresnel Lens: A device comprised of a large number of closely spaced circles cut into one surface of a sheet of acrylic which can reduce the incident bend angles of light rays emanating from a projection source placed behind it. The Fresnel Lens tunnels light to the viewing area so that none is lost on the floor or ceiling or walls. 

Gain: A measurement usually made perpendicular to screen center of the luminance transmitted by a screen, dividing by the luminance radiating from the projector. Matte white or unity gain is 1.0 gain. The measurement calibration is magnesium carbonate. As gain increases the viewing angle narrows. 

Harmonics Integral multiplies of a fundamental frequency are harmonics of that frequency. A pure Sine wave is free of harmonics. Adding harmonics to a fundamental frequency will change its wave shape. A square wave contains a fundamental frequency plus all the odd harmonics of that frequency.

HDTV (High Definition Television) There are any number of specifications that could apply to this term. In 1941, our current 525 line system was referred to as HDTV. Today, this name is applied to several expanded resolution systems that are coming into place for our future entertainment and information delivery system(s). Several of the proposed HDTV systems claim to have a picture resolution equal to that of a projected 35 mm film print.

High Voltage (EHT) A large positive charge at the face plate of a CRT; in the order of 14,000 to 31,000 volts, is necessary to attract the electron beam from the neck of the picture tube to the front surface of the tube. There is a separate power supply in most CRT based viewing devices that supply this voltage. Large CRT's usually require higher voltages. High light outputs on any CRT requires more power from the high voltage supply than low light outputs. High voltage is also known as Extremely High Tension, EHT. VE T11.

Horizontal Blanking (Retrace) The process of bringing the electron beam in a CRT back to the left side of the screen after a left to right line has been traced on the screen. The beam is shut off, blanked, during the period of retrace. About 83% of the total horizontal line time is spent writing the line. The remaining 17% is spent bringing the beam back to the left side; retrace, before starting the next line. See Horizontal Scanning Frequency below.

Horizontal Resolution, detail in transitions in the horizontal direction, is partially determined by Contrast level. It goes down as contrast goes up. In the video world, horizontal resolution is measured in terms of a distance along the horizontal axis equal to the height of the picture. If we say that a picture has 425 lines of horizontal lines per picture height, 425 lines would be exhibited to about 3/4 of the way across the picture. Horizontal resolution is measured in terms of picture height because the width of the line is 1.33 time the height. Larger numbers in the horizontal direction would be more difficult to interpret in terms of overall picture resolution if they were not expressed in terms of the height.

The computer world chooses to specify horizontal resolution across the entire width of the line. A 640 by 480 picture has an equal picture resolution capability in both the horizontal and vertical direction. Who would ever guess that by looking at the numbers? If that were specified the way it is done in the television world, the horizontal resolution would be 480 lines per picture height and the vertical resolution would be 480 lines.

Horizontal Scanning Frequency In the early days of black and white the horizontal scan rate was a multiple of the number of lines and pictures per second. There were 30 complete pictures per second and 525 lines per picture therefore the horizontal frequency was 30 x 525 or 15.750 KHz. The horizontal scan rate in our NTSC color system is derived from the color subcarrier. The formula is (3,579,545 Hz)(2/455) = 15,734.26 Hz. The horizontal frequency is expressed as 15.734 KHz.

The factor of 2 used in the derivation puts the harmonics of the color information in-between the harmonics of the horizontal interval. That allows the use of a comb filter decoder in pulling color information out of the composite signal, while preserving some of the luminance information in that same frequency space.

The factor of 455 was chosen in the original system design to put the color subcarrier frequency at a point low enough where it would not interfere with the audio carrier of a television transmitter, and yet high enough allow compatibility with existing black & white TV sets.

Each complete horizontal line is 63.55 microseconds (.00006355 seconds) long. About 10.9 microseconds of that time is used for horizontal blanking, the time that the horizontal line is retraced from the right side back to the left. The color burst occupies 2.5 microseconds of that horizontal blanking interval.

See Picture Frequency below for additional details.

Hue (Hue or Tint Control) Red, yellow, blue, etc. are hues of color or types of color. Hue is the parameter of color that allows us to distinguish between colors. On the CIE diagram, it is the dominant wavelength of a color. On a TV set, the hue or tint control changes the color; as an example, being able to adjust flesh tone from green to purple. VE T12-13.

IEEE (Institute of Electrical & Electronics Engineers) It promotes the engineering process creating, developing, integrating, sharing, and applying knowledge about electrical and information technologies and sciences for the benefit of humanity and the profession.

One of its standards in common use in the digital video world in the IEEE 1394 "Firewire" digital interface.

ILA� (Image Light Amplifier) A JVC lightvalve technology for video projection. See D-ILA above.

Interactive Video Disc A Video Standard or Video Essentials do not play through from beginning to end without requiring the viewer to make some decisions about the direction of the program. Interactivity between the disc's program content and the viewer is required. There are three basic levels of interactivity. Both A Video Standard and Video Essentials on laserdisc are Level 1 programs; interactivity is manual, via the player's remote control. Level 2 discs incorporate a separate interactive program on the disc itself. Each time the disc is placed in a special Level 2 player, the programming information from the videodisc is loaded into the player's memory. Level 3 has an outboard program to run the disc.

The standard consumer DVD has its own built in program running the disc. In laserdisc terms, all DVD's would at least qualify as Level 2 discs.

Interlace In our current video system a picture is "written" on the display device in two halves. Interlace is the process of placing lines of the second half of the picture in-between lines of the first half of the picture. NTSC is a 2:1 interlace system.

Invar: This is an expensive, brittle metal used to make the shadow mask in a direct view color picture tube. Incorporating it allows higher picture contrast levels from the tube without incurring long-term damage to the shadow mask itself. It allows the set manufacturer to offer you ever higher contrast levels. Since the phosphors in the tube reach the point of blooming well before the need for the Invar mask, anyone properly setting the contrast level for no blooming in the picture won't ever need the features of the Invar mask. The high contrast levels permitted by the Invar mask will eventually burn the phosphors.

An Invar shadow mask has the potential of slightly degrading the picture quality when compared to a standard, well made shadow mask. The Invar brittle metal is difficult to drill, therefore the holes in the mask are not as well formed as they should be in a conventional shadow mask. This causes slight distortions in the picture. They of course would be hidden if the contrast were run high enough to need the assets of the Invar metal. If this Invar "feature" were to be removed from high end sets, real picture quality would go up slightly, and the cost to the manufacturer would go down.

A large number of expensive sets, having many other desirable features, come with an Invar shadow mask. Its presence is not a reason to avoid the set, just an expensive option that you shouldn't need. If your set has to compete with sunlight, look for the Invar shadow mask. You'll need it.

IRE (Institute of Radio Engineers) 1 Volt Peak - Peak Video is divided up into 140 IRE units. This is done to make numbers for luminance levels easier to communicate. The amplitude of the video signal from blanking (zero volts) to peak white is 0.714286 volts or 100 IRE units. Synchronization signals extend from blanking to - 0.285714 volts or - 40 IRE units.

• Picture Black Level: 7.5 IRE (above zero volts)
• Picture White Level: 100.0 IRE (above zero volts)
• Blanking Level : 0.0 IRE (zero volt level)
• Burst Pedestal : 0.0 IRE (zero volt level)
• Synchronization :- 40.0 IRE (below zero volts)

The SMPTE component video system does use the IRE system to define video levels. It is based on a 700 mVolt system rather than the 714 mVolt composite video.

ISO "ISO" is a word derived from the Greek isos, meaning "equal". It is the root of the prefix "iso-", as in "isometric" (of equal measure or dimensions) or "isonomy" (equality of laws, or of people before the law). The choice of "ISO" as the name for the organization implies "equal" or "standard". It also avoids the plethora of acronyms resulting from the translation of the actual name of the organization, "International Organization for Standardization". (It would be IOS in English and OIN in French; Organisation Internationale de Normalisation).

The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies from some 130 countries, one from each country. ISO is a non-governmental organization established in 1947. Its mission is to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological and economic activity.

ISO's work results in international agreements that are published as International Standards.

The scope of ISO covers all technical fields except electrical and electronic engineering, which is the responsibility of IEC. A joint ISO/IEC technical committee carries out the work in the field of information technology.

Among well known ISO standards are:

The ISO film speed code, among many other photographic equipment standards, has been adopted worldwide.

The ISO 9000 business standards that provide a framework for quality management and quality assurance.

ITU (International Telecommunications Union) The ITU, headquartered in Geneva, Switzerland is an international organization within which governments and the private sector coordinate global telecom networks and services.

The ITU-T fulfils the purposes of the ITU relating to telecommunications standardization by studying technical, operating and tariff questions and adopting Recommendations on them with a view to standardizing telecommunications on a worldwide basis. It has taken up many of the documents originally assembled by the CCIR.

JPEG (Joint Photographic Experts Group) This was (and is) a group of experts nominated by national standards bodies and major companies to work to produce standards for continuous tone image coding. The 'joint' refers to its status as a committee working on both ISO and ITU-T standards. The 'official' title of the committee is ISO/IEC JTC1 SC29 Working Group 1, and is responsible for both JPEG and JBIG standards.

The best known standard from JPEG is ITU-T T.81, which is the first of a multi-part set of standards for still image compression. A basic version of the many features of this standard, in association with a file format placed into the public domain by C-Cube Microsystems (JFIF), is what most people think of as JPEG.

Laserdisc An analog video optical disc format. Full bandwidth composite video plus two analog audio tracks were recorded on the original disc format. It was later expanded to include digital audio capability. First came the PCM tracks with a specification similar to CD audio. The next step was Dolby Digital occupying the space of one of the analog audio channels. The only analog audio possible in this configuration was a single monaural channel. In some discs the PCM track was replaced by DTS multichannel digital audio. These discs usually had both analog audio channels to make the discs playable where a DTS decode capability wasn't available. The format itself was introduced to the consumer market by MCA DiscoVision in December of 1978 in Atlanta, Georgia. It fell by the wayside as a viable consumer product shortly after the introduction of DVD in 1997. By the middle of 2000 most studios stopped making titles available for the format.

LCD (Liquid Crystal Display) Created by sandwiching an electrically reactive substance between two electrodes, LCDs can be darkened or lightened by applying and removing current. Large numbers of LCDs grouped closely together can act as pixels in a flat-panel display.

Letterbox The projected aspect ratio of feature films is often wider than our 525 or 625 line video formats. It is becoming common practice to transfer the composed aspect ratio of films to video by placing black boarders at the top and bottom of the film picture in the video. The film picture becomes a "letterbox" within the video.

Light Valve Technology A light valve projector uses a bulb as the source of light. The valve technology changes the color and intensity of the source to form the picture. Film or slide projectors are examples of light valve technology. The Digital Micro-mirror Device (DMD); also know as the Digital Light Processor (DLP), the Image Light Amplifier (ILA), and LCD are all examples of electronic light valve technology.

Obtaining black in a picture produced by a light valve projector requires an ability to shut the light off in particular areas of the picture. Shutting light off in a small area is actually rather difficult. Consequently, the real picture contrast ratio of a number of these projectors is rather poor.

Looping The process of continuously repeating a program segment from point A to point B.

Luminance This is the signal that represents brightness in a video picture. Luminance is any value between black and white. In mathematical equations, luminance is abbreviated as Y.

Monitor A CRT based picture display device that accepts a baseband video, component video or a digital video signal as an input. A Receiver/Monitor can accept an RF input and baseband video.

MP3 (MPEG-1, Layer 3) Using MPEG audio, one may achieve a typical data reduction of 1:4 by Layer 1 (corresponds with 384 Kbps for a stereo signal), 1:6...1:8 by Layer 2 (corresponds with 256..192 Kbps for a stereo signal), 1:10...1:12 by Layer 3 (corresponds with 128..112 Kbps for a stereo signal).

By exploiting stereo effects and by limiting the audio bandwidth, the coding schemes may achieve an acceptable sound quality at even lower bitrates. MPEG Layer-3 is the most powerful member of the MPEG audio coding family. For a given sound quality level, it requires the lowest bitrate - or for a given bitrate, it achieves the highest sound quality.

For the use of low bit-rate audio coding schemes in broadcast applications at bitrates of 60 Kbit/s per audio channel, the ITU-R recommends MPEG Layer-3. (ITU-R doc. BS.1115)

MPCD (Minimum Perceptible Color Difference) This is a unit of measure, developed by the CIE, to define the change in light and color required to be just noticeable to the human eye. The human being in this MPCD unit is defined as "a trained observer" because there are differences in the way each of us perceives light.

MPEG (Motion Picture Experts Group) It is the nickname given to a family of International Standards used for coding audio-visual information in a digital compressed format. MPEG standards include MPEG-1, MPEG-2 and MPEG-4, formally known as ISO/IEC-11172, ISO/IEC-13818 and ISO/IEC-14496.

MPEG is originally the name given to the group of experts that developed these standards. Established in 1988, the MPEG working group (formally known as ISO/IEC JTC1/SC29/WG11) is part of JTC1, the Joint ISO/IEC Technical Committee on Information Technology.

MPEG-1, is the standard on which such products as Video CD and MP3 are based. MPEG-2 the standard on which such products as Digital Television set top boxes and DVD are based and MPEG-4, the standard for multimedia on the web. The current thrust is MPEG-7 "Multimedia Content Description Interface".

NAB (National Association of Broadcasters) The National Association of Broadcasters represents the radio and television industries in Washington -- before Congress, the FCC and federal agencies, the courts, and on the expanding international front. NAB provides leadership and its vast resources to our supporting members, to broadcasters at-large, and through ongoing public service campaigns to the American people.

NTSC (National Television System Committee) The organization that developed both our American Black & White and Color television system is the National Television System Committee. Our television system, itself, has become known as NTSC. Other countries such as Canada, Mexico, and Japan have also standardized on NTSC. (The word "System" is sometimes printed in the plural form.) NTSC is also known as "Never Twice the Same Color" as a result of some of the problems encountered in implementing the system.

NTSC Decoder: An electronic circuit that breaks down the composite NTSC video signal into its components. It挿�s the receiver side of the encode, decode process used to compress three channels of color information into one, then expand it back to the three channels required for viewing. There are two basic types of decoders, Comb Filter and Notch Filter. There are a nu