Digital TV Glossary
To help you better understand KQED's transition to digital technology, here are some terms you may be seeing in the coming months.
Advanced Digital Television (ATV):
The FCC's original name for Digital Television (DTV).
Advanced Television Systems Committee (ATSC):
The current digital United States television standards (HD, SD and Data).
The technology in use for more than 50 years to transmit conventional TV signals. Vinyl recordings and audio cassettes are also examples of analog technology.
The ratio of screen width to screen height. For HDTV, the aspect ratio is 16:9 (16 units wide by 9 units high), much like a movie screen. Today's analog television screens are 4:3, or nearly square.
A means of communication from users back to content providers. At the same time that content providers are transmitting interactive television (analog or digital) to users, users can connect through a back channel to a Web site - for example, to the original content provider or an advertiser. The back channel can be used to provide feedback, purchase goods and services, request more information, play games and so on. A simple type of back channel is an Internet connection using a modem.
The amount of spectrum available to each communications licensee. For digital conversion, the FCC has allocated 6 MHz (megahertz) of the broadcast spectrum for each television broadcaster. That channel will carry 19.4 Mb/s of data. It can be used for one HDTV signal, or four multicast digital signals, and/or data transmission.
As in television channel; the television broadcast frequency. The over-the-air television channel assignments are set by the FCC and are currently found in the VHF or UHF band. Each television broadcast station is being assigned a matching channel for DTV.
The DTV Channel assignment is different than the channel currently being used by the analog station. KQED's assigned DTV channel is 30. However, KQED transmits its "virtual ID," which designates the channel as 9.1, 9.2, etc.
During the transition period, U.S. television stations will be able to broadcast on their current channel and their new DTV frequency. At the end of the transition, the stations will broadcast only their DTV signal.
The broadcast of information services through a television channel. Because digital broadcasters can send more data over the airwaves, viewers get a lot more than just television. Broadcasters can use their bandwidth to offer additional data or services.
For example, a travel program might be transmitted along with data consisting of lodging, sightseeing and transportation information, which the viewer can access while watching the program. Teachers will be able to access lesson plans and learning materials while watching TV. This information might appear as a menu of choices on the TV or computer screen, which the viewer can read on the screen, store on a hard drive, or print out for future reference.
One of the major benefits of a digital broadcast system is the ability not only to send pictures and sound, but also to send data. Program related data enhances the television show you are currently watching. For instance, Real Science could include science quizzes for teachers, periodic table graphs, a molecule building game, audio clips of various animal vocalizations, or anything else you can imagine that can be transmitted digitally.
Descriptive Video Information (DVI):
Some programs provide an additional narration, which enables visually impaired persons to hear enriched verbal descriptions of the action being seen on the program. Most TVs and VCRs require that you select the SAP channel in order to receive DVI. DVI used to be called DVS.
Digital Television (DTV):
Refers to transmitting a broadcast signal by encoding it as 0s and 1s - the digital binary code used in computers. DTV can provide high quality programming (HDTV) or provide four, five or more channels in the same bandwidth required for one channel of the current analog television. Calculators, computers, compact discs and the Internet are examples of digital technology.
Digital TV Tuner:
The receiver or tuning part of a TV set. May be sold separately.
The picture part of a Digital TV set. May be sold separately.
Federal Communications Commission (FCC):
Independent US government agency, directly responsible to Congress and charged with regulating local, interstate and international communications by radio, television, wire, satellite and cable. The FCC's jurisdiction covers the 50 states, the District of Columbia, and U.S. Possessions.
Flat Screen Display:
Television screens that flatten the shape of television sets to that of a framed picture. The screens on yesterday's television sets use bulky cathode ray tubes (CRTs). CRTs are made of a glass envelope and use a controlled beam of electrons striking light-emitting material to display the picture. Flat screen displays use plasma display systems or LCD displays.
High Definition Television (HDTV):
Offers approximately twice the vertical and horizontal resolution (clarity) of NTSC television. Provides crystal-clear widescreen pictures with compact disc-quality surround sound. The aspect ratio of HDTV pictures is 16:9, similar to a movie screen's dimensions, as opposed to the 4:3 format of today's television. HDTV approaches movie theater display quality. The HDTV standard can also use 5.1 channels of CD-quality sound plus additional SAP channels.
A combination of television with interactive content and enhancements. Interactive television provides better, richer entertainment and information, blending traditional TV-watching with the interactivity of a personal computer. Programming can include graphics, one-click access to Web sites through TV crossover links, electronic mail and chats, and online commerce through a back channel. Some applications may be displayed on TVs, others on computers.
A system which skips every other line of a picture on the first pass, then fills in those lines on the second pass. When talking about resolution, this method is indicated by an "i" after the number of lines, as in "480i" or "1080i".
When you watch analog television, you're looking at an interlaced video display. Because early television tubes couldn't draw the whole screen before the top began to fade, TV engineers implemented interlacing. On some digital TVs, as on computer monitors, the whole screen is "progressive" (drawn line by line, top to bottom).
When a widescreen picture is viewed on a 4:3 TV screen, a black border may appear at the top and bottom of the screen creating a "letterbox" effect, but allowing the viewer to see the whole width of the wide-screen image.
For example, this allows movies to be broadcast as originally formatted for theaters, allowing the viewer to see the image as originally produced, rather than a cropped or "panned and scanned" version (techniques used to downsize an image to fit a 4:3 screen).
Liquid Crystal Display (LCD):
Flat screen display technology.
Broadcasting several DTV programs at once on a single channel. A KQED-DT viewer might be able to receive Sesame Street and Nova at the same time, and choose the program s/he prefers by selecting that "channel" from our digital bouquet.
National Television Systems Committee (NTSC):
The group that set the analog television standard 50 years ago. The abbreviation is used to refer to the current US standard.
Near Video On Demand (NVOD):
Usually describes a service where a provider (e.g. cable company) starts the same movie at closely staggered times (e.g. 9pm, 9:05pm, 9:10pm, etc.), so that a viewer who wants to see the movie need wait only a few minutes at most to see it.
Nonlinear distinguishes editing operation from the "linear" methods used with tape. Nonlinear refers to not having to edit material in the sequence of the final program and does not involve copying to make edits. It allows any part of the program to be accessed and modified without having to recopy the material that is already edited. Nonlinear editing is also nondestructive, as it uses computer hard disks to play this material in the random access order the editor has selected rather than playing a linear videotape.
A decision-making process using low-cost equipment to produce a rough cut "edit decision list," which can then be used to make the high quality final version of the program.
Personal Video Recorder (PVR):
STB which records programs onto an internal hard-drive to be played back at viewer's convenience (e.g. TiVo system or ReplayTV).
A shortened version of "picture element," the smallest element in a television picture. The total number of pixels limits the detail that can be seen on a television. A typical television set has the equivalent of less than half a million pixels. The pixel count for HDTV is over two million.
Flat screen display technology. Most susceptible of the flat screens to having frequent images (e.g. picture frame edges and white logos) becoming "burned into" the display.
Program and System Information Protocol (PSIP):
A DTV-required signal which contains various lists of information needed by the receiver. The signal is transmitted from the program supplier (network, station, or cable system) to the viewer's receiver or STB. The signal contains information for the TV set about where to find the program (e.g. telling the set that channel 9.2 really comes from DTV channel 30). The PSIP signal also announces the content of present and future programs for the viewer including: program titles and promotional material, duration of the programs, and time of day. PSIP also helps the TV set know about the contents of the signal (e.g. closed captioning, type of audio, where to find the program within the channel).
The ability of most computer monitors and high resolution sets to display all the lines of a picture at the same time. When talking about resolution, this method is indicated by indicated by a "p" after the number of lines, as in "720p".
A measure of the finest detail that can be seen, or resolved, in a reproduced image. While influenced by the number of pixels in an image (for HDTV 1920 x 1080; current broadcast NTSC TV 640 x 480), the pixel numbers do not define ultimate resolution but merely the resolution of that part of the system. The quality of lenses, display tubes, film process and film scanners, etc., used to produce the image on the screen must all be taken into account.
Secondary Audio Programming (SAP):
Options offered on some programs accommodated by recent TVs and VCRs, including sound with video description for the vision impaired, a director's narration, foreign language narration, or other possible services. May be called MTS (Multi-channel TV Sound) or 2nd Channel Sound on some sets.
A storage system that provides data files to all connected users of a local network. Typically the file server is a computer with large disk storage which is able to record or send files as requested by the other connected (client) computers. The file server often appears as another disk on client systems. The data files are typically around a few kilobytes in size and are expected to be delivered within moments of request.
A storage system that provides audio and video storage for a network of clients. While there are some analog systems based on optical disks, most used in professional and broadcast applications are based on digital disk storage.
Aside from those used for video on demand (VOD), video servers are applied in three areas of television operation: transmission, post production and news. Compared to general purpose file servers, video severs must handle far more data, files are larger and must be continuously delivered. Store sizes are very large, typically up to 500 gigabytes or more.
Set-Top Box (STB):
A box which decodes or otherwise translates the signals coming to it so they can be used by the customer's TV set.
The set top box may provide functionality of translating HD signals to analog, may allow interactivity, may allow tuning of other channels, may allow reception of VOD, reception of pay-per-view channels, may contain a hard-disc to provide storage of data or time-shifting of programs (e.g. PVRs). The STB may contain a modem for connection via telephone line for ordering services or other upstream communication.
To broadcast the same program over two different transmission systems at the same time. Currently, some AM and FM radio stations simulcast the same program for part of the day. The FCC plans to have mandatory simulcast of analog programming over the new DTV system. This requirement should speed the transition to DTV.
Standard Definition Television (SDTV):
A digital television system that is similar to current standards in picture resolution and aspect ratio. The picture and sound quality will be clearer than NTSC. It offers the ability to transmit four or more standard-quality programs at once (equivalent to NTSC), using the digital channel. SDTV also incorporates stereo sound plus a wide range of data services.
1. To transmit multimedia files that begin playing upon arrival of the first packets, without needing to wait for all the data to arrive.
2. To send data in such a way as to simulate real-time delivery of multimedia.
Video On Demand (VOD):
A service which allows viewers to receive and play programs (usually movies) at their convenience from cable. May allow viewer to stop, pause, play, rewind, etc.
Term given to picture displays that have a wider aspect ratio than normal. Historically, TV's normal aspect ratio is 4:3 and widescreen is 16:9. Although this is the aspect ratio used by HDTV, widescreen is also used with normal definition systems.
Widescreen SD Programs:
Term used by PBS to denote programs produced in the widescreen aspect of 16:9, but not broadcast in HDTV.