Glossary of Terms for DTV and HDTV Consumers
8-VSB: Acronym for the transmission method used for over-the-air DTV broadcasting in
AC-3: The 5.1-channel compressed digital sound system specified for DTV broadcasting in
Addressable Resolution: The highest resolution signal that a display device (television or monitor) can accept as input. Some display devices may not be capable of displaying such signals and may downconvert them to a lower resolution prior to display.
Analog Video: The conventional NTSC television system in use today uses analog technology, in which the image sound and the picture brightness and color are represented by signals proportional to these values. The values of these signals are vulnerable to interference and noise. Digital television overcomes this vulnerability and delivers signals that are totally clean.
Artefacts: Unwanted visible effects in the picture created by errors in the video processing or noise/interference in analog circuits. Common artefacts include edge crawl or hanging dots in analog pictures or blockiness, noise or contouring in digital pictures.
Aspect Ratio: the ratio of image width to image height. The term may apply to the display device configuration, or the shape of the content being displayed. (See Letterboxing) HDTV uses an aspect ratio of 16 units wide by 9 units high. Conventional television programming and displays are at an aspect ratio of 4:3. Digital SDTV programs may aspect ratios from 4:3 to 16:9, dependant on content and its source (e.g. upconverted NTSC is likely to be 4:3).
ATSC: "Advanced Television Systems Committee." Formed to establish technical standards for
Bandwidth: The range of frequencies used to transmit the television signal, including picture and sound. Analog television signals have been allocated at 6 Megahertz for each over-the-air channel. Digital channels are allocated the same 6 Megahertz by Industry
Baseband Video: Unmodulated analog video signal.
Bit Rate: The rate at which the data is transmitted, expressed as "bits per second" (bps). The higher the bit rate, the more data that is transmitted, generally resulting in better picture or sound quality. Video data rates are usually expressed as Megabits per second (Mbps, 106) and audio data rates in kilobits per second (kbps, 103).
CDTV: Canadian Digital Television, a not-for-profit, government-approved body, with members from all sectors of the TV industry. CDTV is mandated to advise its members, Industry
Closed Captioning: A data stream included in broadcast signal that provides text and/or narrative description of dialogue, sounds, and other elements of the picture for viewers with visual or auditory impairments.
Composite Video Connection: A method to interconnect video devices (such as a DTV set-top box and the analog television) by sending the signal over a single cable. This method is suitable only for analog NTSC signals
Compression: A method of reducing the number of bits required to store or transmit programs by the removal of redundant and/or non-critical information in the digital picture and sound. The DTV broadcasting standard for
CRT:An analog vacuum tube technology that has been the mainstay of conventional TV displays for many years, writing the picture on a phosphor coated screen with an electron beam. It can produce bright pictures of excellent resolution but the size and weight of a unit suitable for the large, wide-screen displays needed for HDTV may be, for some, a disadvantage.
Datacasting: The inclusion of additional data in the broadcasting stream. Such data may be related to the current program (e.g. sports statistics) or may be completely independent (e.g. software downloading or traffic advisories).
DLP (Digital Light Processing):A technique in which the displayed image is produced by an array of dynamic micro-mirrors formed on a chip, each reflecting some of the light source to form a pixel on the screen. Each micro-mirror controls the level of the light sent to the screen for its pixel. Resolution is set by the size of the mirror array and versions suitable for wide-screen HDTV are now in production for uses in both front and rear projection televisions.
Dolby Digital (Dolby AC-3): The 5.1 channel audio standard for DTV and HDTV in
Dot Pitch: The distance between pixels (picture elements) in a display. In a CRT for HDTV, the dot pitch is typically 0.25 - 0.3 mm. For full resolution HDTV display approximately 1400 pixels are required across the screen.
Downconvert: The process which reduces the number of pixels in the scanning format used to represent an image, so that it may be reproduced on a display of lower resolution, such as a conventional television. For example, an HDTV image may be downconverted to an SDTV or NTSC image, but in the conversion significant detail information may be lost.
DTS: Digital Theatre Sound System. A Dolby proprietary discrete 5.1 channel surround system similar to, but not the same as Dolby Digital AC-3, the DTV standard. DTS is used in cinema presentations and in DVD's.
DVD: Digital Versatile Disk. An optical recording media similar to the familiar CD but having seven times its capacity on a single side. In television applications, DVD's are capable of carrying full-length commercial movies, plus additional material such as outtakes, director
EDTV: Enhanced Definition Television. A term defining a television that displays the picture (either from SDTV or HDTV) at a resolution of 480p lines in either 4:3 or 16:9 aspect ratio and which includes Dolby Digital AC-3 multichannel sound.
Encryption: The process of coding signals so that a specific code or key is required by the viewer to recover the data so encrypted. Without this key, the data is meaningless. Encryption is used to provide conditional access for private television services.
Fire Wire: A digital interface originated by Apple Computer that can transport data at 100, 200, or 400 Mbps. It is widely used to interconnect digital video devices, such as cameras and displays. Also referred to as IEEE- 1394.
Fps: Frames per Second. To give the illusion of motion, television actually transmits a series of snapshot pictures referred to as frames. Increasing the frame rate improves motion smoothness and may reduce flicker in some displays. In
HDTV: High Definition Television: HDTV is a TV system having approximately twice the vertical and horizontal picture resolution of today
Interlaced Scanning: Some HD televisions and most conventional televisions use the "interlace" method of scanning, in which the picture is transmitted and painted on the screen in two passes. In the first pass, every other line is painted and in the second, the lines in between. Some display types, such as LCD, plasma and DLP cannot display directly images transmitted as interlaced signals and must convert them to a progressive format prior to their display.
Letterbox: The full display of a wide aspect ratio 16:9 picture on a display of aspect ratio 4:3 will result in black bars above and below the picture. This arrangement is referred to as "Letterbox" and is often seen during movies shown on television.
LCD. (Liquid Crystal Displays): A flat panel technology, using thin-film crystal techniques, widely used in laptop computers, other small portable displays and more recently in televisions. Image brightness can be very high and color performance can be good. For HDTV, wide-screen displays of adequate resolution are available up to about 94 cm (37 in.) for direct viewing. LCD devices are also widely used as the key element in many projection televisions, both front and rear screen, up to very large sizes.
MPEG-2: Compression standards for moving images and for audio as set by Motion Pictures Expert Group (MPEG). MPEG-2 video coding is the basis for ATSC digital television transmission in the U.S and
NTSC: National Television Systems Committee. The organisation that created the standards for production and broadcasting of analog color television programming in
Over-the-air Broadcast (OTA): Also called Terrestrial Broadcast. The delivery of TV and radio signals, using UHF/VHF frequencies, directly to consumer devices. Broadcasts may be either analog or digital.
Plasma Displays (PDP). A technique that builds an image from a large number of pixels formed in a glass panel. The pixels are individually controlled, yielding a picture free of flicker and of high brightness. Displays of excellent resolution and color are available and the display approaches the "television picture on the wall" ideal. PDP displays up to 160 cm (63in.) are available, making them suitable for the home theatre.
Progressive Scanning: Some HD televisions use the "progressive" method of scanning, in which the whole picture is transmitted and presented on the screen in one pass. The resulting image is thus remarkably free of flicker and motion artefacts, appearing more "life-like". Some display types, such as LCD, plasma and DLP are inherently of the progressive scan type, while CRT's may be scanned progressively (as in computer monitors) or interlaced.
PSIP: Acronym for "Program and system information protocol", an ATSC DTV specification that enables a DTV receiver to identify the program information and to create on-screen electronic program guides and content advisories.
Resolution: A measure of the density of lines and dots per line which make up a visual image. Usually, the higher the numbers, the sharper and more detailed the picture will be. In terms of DTV, maximum resolution refers to the number of horizontal scanning lines multiplied by the total number of pixels per line.
Reverse 3:2 Pull-Down: DTV material originating on film at 24 fps is converted to the 30 fps of DTV by repeating field or frames, resulting in some motion artefacts. Some film presentations remove these repeated images before transmission and send a signal to the television causing it to process (termed Reverse 3:2 Pull-Down) this material appropriately to make it suitable for display. In this way, the displayed material closely matches the original film quality, avoiding the motion artefacts.
SDTV: "Standard Definition Television." SDTV are based on 480 lines of vertical resolution and may have either 4:3 or 16:9 aspect ratios, and surround sound. Several SDTV programs are sent together to form the simulcast bundle. While SDTV pictures are of significantly better quality than NTSC, they are not up to the standard of HDTV.
Set-top box (STB): A box, similar to the familiar cable box, that is capable of receiving, decoding and sending to the associated television the picture and sound of the selected DTV broadcast. The use of an STB would allow the use of conventional televisions to receive DTB programs, but at reduced levels of resolution and with imperfections due to aspect ratio differences, leading to letterboxing or cropping of the sides of the picture.
Simulcast: The broadcast of the same program simultaneously over two or more different systems or channels, such as in HDTV and in NTSC. CRTC regulations require today that broadcasters simulcast much of their schedules.
S-Video Connection: A method to interconnect video devices (such as a DVD player and the analog television) by sending the two signals luminance (Y) and an encoded color difference signal (C). The S-Video connection is made using a cable terminated in a small 4-pin connector (in some cases a 7 pin connector is used on computers to allow inclusion of an NTSC composite signal). S-video can greatly improve the picture when connecting SDTV or NTSC displays to a high quality video source such as DVDs.
Upconvert: The process which increases the number of pixels or frame rate used to represent an image by creating new pixels at closer spacing. For instance SDTV video having 720 x 480 pixels may be upconverted to 1280 x 720 pixels for use as HDTV. The upconversion process does not increase the resolution of image.
Video-on-Demand (VOD): A programming library service offering the individual viewer the choice of the available content on demand. When the program is requested and confirmed (by telephone or Internet) it is then delivered to the viewer over an available channel in encrypted form. VOD services are generally arranged on a "Pay per View" basis, analogous to the cinema.
Y, PB, PR: A method for carrying the video between HDTV or SDTV devices that retains the maximum quality and is recommended for HD television. The video is carried on three cables, respectively carrying luminance (Y) and the two color difference signals (PB, PR).