Aspect ratio of the NTSC TV screen, with "4" unit width corresponding to "3" unit height, proportionally, regardless of the actual size of the screen.

Aspect ratio of widescreen DTV formats for all HDTV and some SDTV (Standard Definition) video. "16" unit width corresponds to "9" unit height, proportionally, regardless of the actual size of the screen.

Eight discrete amplitude level, "vestigial side-band" broadcast transmission technology. VSB is an analog modulation technique used to reduce the amount of spectrum needed to transmit information through cable TV, or over-the-air broadcasts used in the NTSC (analog) standard. 8-VSB is the U.S. ATSC digital television transmission standard.

8-VSB and COFDM are two possible methods of delivering DTV broadcasts to the home. Each method has advantages which vary depending on the applications for which they are used. 8-VSB is a single carrier modulation system and COFDM is a multi-carrier system. Multiple carriers allow information to be divided among the carriers which, under certain circumstances, makes the system more resistant to multipath (ghosting) reception conditions.

A formula or set of steps used to simplify, modify, or predict data. Complex algorithms are used to selectively reduce (compress) the high digital audio and video data rates. Algorithms are formulated to selectively reduce the data rate without affecting picture quality.

Defects or distortion in a television picture or audio. In digital video, aliasing is caused by insufficient sampling or poor filtering of the digital video. Defects are typically seen as jagged edges on diagonal lines and twinkling or brightening.

Undesirable elements or defects in a video picture. Most common in digital are macroblocks, which resemble pixelation of the video image, and pops and clicks in audio.

American Standard Code for Information Interchange. A standard code for transmitting data, consisting of 128 letters, numerals, symbols, and special codes, each of which is represented by a unique binary number. An ASCII word typically is 8 bits of binary data.

The ratio of a television picture width to height. In NTSC video, the standard is 4:3. In HDTV and SDTV widescreen video, it is 16:9.

Lacking synchronization. In video, a signal is asynchronous when its timing differs from that of the system reference signal.

"Advanced Television Systems Committee." Formed to establish technical standards for U.S. advanced television systems. Also, the name given to the 8-VSB transmission standard itself.

A means of communication from users to content providers. Today, a simple type of back channel is an Internet connection using a modem.

The complete range of frequencies over which a circuit or electronic system is allocated to function. In transmission, the U.S. analog and digital television channel bandwidth is 6 MHz.

A unit of signaling speed equal to the number of signal events per second. Baud is equivalent to bits per second in cases where each signal event represents exactly one bit.

"Bit error rate." Bit errors are caused by interference, or loss of signal, so the stream of bits composing the DTV picture is disrupted. A measure of the errors in a transmitted signal.

An analog video taping system using a 1/2-inch tape cassette, developed by Sony. Digital versions include Digital Betacam and Betacam SX.

A numbering system using the digits "0" and "1" in the decimal system. All computer programs are executed in binary form.

Binary digit. The smallest unit of data in a digital system. A bit is a single one or zero. A group of bits, such as 8-bits or 16-bits, compose a byte. The number of bits in a byte depends upon the processing system being used. Typical byte sizes are 8, 16, and 32.

Capable of handling frequencies greater than those required for high-grade voice communications.

A group of data bits that are processed together. Typically, a byte consists of 8 bits. There are kilobytes, Megabytes, Gigabytes, Terabytes, etc. 1 Byte = 8 bits

A data modem that uses the bandwidth of a given cable system. Because cable modems provide Internet access over cable, they are much faster than modems that use typical phone lines.

"Consumer Electronics Association." An industry group that represents manufacturers of consumer electronics products.

The process of overlaying one video signal over another, the areas of overlay being defined by a specific range of color, or chrominance, on the foreground signal.

An RF (radio frequency) characteristic that causes DTV reception to deteriorate dramatically with a small change in signal reception. Bit error rate increases to the point where video cannot be obtained by the receiver. The picture and audio are lost entirely.

Text stream included in broadcast signal that provides narrative description of dialogue, action, sounds, and other elements of the picture. Most often used by the hearing impaired and in environments where audio is undesirable (such as in restaurants).

"Coder-decoder." A device that converts analog video and audio signals into a digital format for transmission. Also converts received digital signals back into analog format.

"Coded orthogonal frequency division multiplexing." COFDM can transmit many streams of data simultaneously, each one occupying only a small portion of the total available bandwidth. The DTV standard used in Europe.

Reduction of the size of digital data files by removing redundant and/or non-critical information ("data" being the elements of video, audio and other "information"). Digital TV in the U.S. would not be possible without compression.

A tape format that is a non-compressed component digital video that has provision for HDTV recording by use of about 4:1 compression (HD D5).

A technique that provides for the transmission or storage, without noticeable information loss, of fewer data bits than were originally used when the data was created.

Enhanced options offered with some digital programming to provide additional program material or non-program related resources, allowing viewers the ability to download data (video, audio, text, graphics, maps, services) to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.

"Direct broadcast satellite." An alternative to cable and analog satellite reception utilizing a fixed 18-inch dish focused on one or more geostationary satellites. DBS typically uses MPEG-2 encoding and QPSK transmission.

Video editing and production using standard desktop computing platforms running with add-on video hardware and software.

Circuitry in which data-carrying signals are restricted to either of two voltage levels, corresponding to logic 1 or 0.

A development of the original analog Betacam that records digitally on a Betacam-style cassette.

A video recording device that uses a hard disk drive or optical disk drive mechanism. Disk recorders offer nearly instantaneous access to recorded material.

The approved 5.1 channel (surround-sound) audio standard for ATSC digital television, using approximately 13:1 compression. Six discrete audio channels are used: Left, Center, Right, Left Rear (or side), Right Rear (or side), and a subwoofer -- LFE, "low frequency effects" -- (considered the ".1" as it is limited in bandwidth).

Matrix analog coding of four audio channels - Left, Center, Right, Surround (LCRS) - into two channels referred to as Right-total and Left-total. The Dolby Surround system originally was developed for motion pictures.

The process that changes the number of pixels and/or frame rate and/or scanning format used to represent an image, by removing pixels.

"Digital television." This comprises all the components of digital television, including HDTV, SDTV, datacasting, and multicasting.

"Digital Versatile Disk." (Formerly Digital Video Disk.) Same size as a CD but stores seven times CD capacity on a single side. DVDs can also be double-sided or dual layer. Today most DVD's are used to display full-length commercial motion pictures, plus additional material such as outtakes, director's notes, movie trailer, etc.

An application that provides an on-screen listing of all programming and content that an interactive television service subscriber or digital television viewer has available to them.

The process of coding data so that a specific code or key is required to restore the original data, used to make transmissions secure from unauthorized reception.

Producers add these options to some digital programming to enhance program material - allowing viewers the ability to download related program resources to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.

Term used by PBS for certain digital on-air programming (usually educational) that includes additional resources downloaded to viewers. Some forms of enhanced TV allow live interaction; other forms are not visible on-screen until later recalled by viewers. Also known as "datacasting."

Thin glass filaments within a jacket or bundle that optically transmit images or signals in the form of light over distances, with extremely low high-bandwidth quality losses.

A low-cost digital interface originated by Apple Computer and further developed by engineers and adopted by CEMA. It can transport data at 100, 200, or 400 Mbps. This is widely viewed as one key solution to connect digital-related TV components with each other. Also known as IEEE-1394.

Process of both encoding/decoding and re-sampling digital rates to change digital data from one format to another.

"Frames Per Second," the number of still frames (pictures) that give the allusion of motion, which appear in a single second of time.

Scattering of data over a hard disk caused by successive recording and deletion operations. Generally this will eventually result in slow data recall - a situation not suitable for video recording or replay.

Video degradation caused by successive recordings (dubs of other dubs) from the master source. This is overcome by digital recording.

U.S. consortium, formed in 1993, to produce "the best of the best" DTV transmission system from among the initially proposed separate systems. Participants were: AT&T, General Instrument Corp., MIT, Philips Consumer Electronics, David Sarnoff Research Center, Thomson Consumer Electronics, and Zenith Electronics Corp. The group eventually proposed the current ATSC digital standard.

"High Definition Television." This is the most superior video picture available in DTV. In the U.S., the 1080i and 720p formats in a 16:9 aspect ratio are the two acceptable HDTV formats. HDTV is a component of DTV.

"Institute of Electrical & Electronic Engineers." A professional organization that helps set transmission system standards.

TV programming with interactive content and enhancements, blending traditional TV viewing with the interactivity of a personal computer.

A system of video scanning where odd- and even-numbered lines of a TV picture are transmitted consecutively as two separate interleaved fields. Interlace is a form of compression and has been used for decades in analog (NTSC) TV.

A general purpose programming language developed by Sun Microsystems and best known for its widespread use on the World Wide Web. Computer programs written in Java can run on any platform type (including set-top boxes), as long as they contain a Java Virtual Machine.

Image of a wide-screen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. Used to maintain the original aspect ratio of the original source (usually a theatrical motion picture of 16X9 aspect ratio or wider).

Feeding (streaming) video/audio or other data to end-users at a specific time (that is, live). Today the term is most often used for on-line services.

Uses JPEG (computer) compressed images as individual still frames for motion. For example, 30 Motion-JPEG frames viewed in one second would approximate 30-fps video.

Compression standards for moving images and audio are set by the Motion Pictures Expert Group (MPEG), an international committee of industry experts. MPEG-2 is the basis for ATSC digital television transmission in the U.S.

Option made possible by digital technology to allow each digital broadcast station to split its bitstream into 2, 3, 4 or more individual channels of programming and/or data services.

"National Television Systems Committee" and the name of the current analog transmission standard used in the U.S., which the committee created many decades ago.

A term used for editing and storage of audio, video and other data. Information (footage, for example) is retrievable and processed almost immediately without having to locate it in a traditional time-line format.

Sending video/audio or other data that is transmitted to the end-user upon request (widely used on news and sports-oriented Web sites, for example).

Refers to "progressive scanning," as in DTV formats 480p or 720p. A system of video scanning whereby lines of a picture are transmitted consecutively (unlike interlaced), as on computer screens.

Set of "rules" defining exchange of data, including timing, format, sequencing, error checking, etc.

Pronounced "P-SIP" - "Program and system information protocol." A part of the ATSC digital television specification that enables a DTV receiver to identify program information contributed by content providers and use it to create sophisticated electronic program guides.

Directly affects picture quality. The higher the resolution, the more picture detail there is. Many things affect resolution, including number of bits, pixel count, format, receiver quality, cameras, lenses and lighting used for live or taped programming, etc.

Abbreviation for red, green and blue signals, the primary colors of light - and television.

Digital process by which analog information is measured, often millions of times per second, in order to convert analog to digital.

"Standard Definition Television." Digital formats that do not achieve the video quality of HDTV, but are at least equal, or superior to, NTSC pictures. SDTV may have either 4:3 or 16:9 aspect ratios, and it includes surround sound. Variations of fps (frames per second), lines of resolution, and other factors of 480p and 480i make up the 12 SDTV formats in the ATSC standard.

System that provides large-capacity audio and video storage for video-on-demand retrieval, transmission, post production, news, etc. Most professional servers use digital disk storage.

Device that converts and displays data from analog cable, digital cable, or digital broadcast television to a standard frequency (channel number) for display on a standard analog television set, or a box that receives off-air DTV signal for display on a DTV monitor.

Used with imaging a standard 4:3 picture on a wide-screen 16:9 aspect ratio television screen, typically with black bars (side panels) on each side. Used to maintain the original aspect ratio of the source material.

The broadcast of the same program simultaneously over two or more different systems or channels. An accelerated amount of simulcasting of both analog and digital programming will be required by FCC rules, during the DTV transition period.

"Society of Motion Picture and Television Engineers." A professional organization that helps set standards for American television.

Electronically improving the quality of an audio or video signal, such as adding sound effects, audio ambience or laugh tracks.

A transmission procedure by which the bit and character stream are slaved to accurately synchronized clocks, both at the receiving and sending end.

"Transmission control protocol/Internet protocol." TCP/IP is a combined set of protocols that perform the transfers of data between two computers.

"Time division multiplex." The management of multiple signals on one channel by alternately sending portions of each signal and assigning each portion to particular blocks of time.

In nonlinear editing, the area in which audio and video clips are applied, typically giving duration in frames and seconds.

Process which increases the number of pixels or frame rate or scanning format used to represent an image by interpolating existing pixels to create new ones at closer spacing. Process does not increase the resolution of image. Upconverting is done from standard definition to high definition.

When video can be requested at any time, solely at the discretion of the end-user (viewer).

"Vestigial side band." VSB is an analog modulation technique used to reduce the amount of spectrum needed to transmit information through cable TV, or over-the-air broadcasts used in the NTSC (analog) standard.

WebTV Networks, Inc. manufactures set-top boxes that allow users/viewers to access the Internet on their NTSC TV receivers.

Term given to picture displays with a wider aspect ratio than NTSC 4:3. Digital HDTV is 16:9 widescreen. Most motion pictures also have a widescreen aspect ratio, some even wider than 16:9.