Glossary of DTV Access Terms
Key concepts to help you "speak geek" (at least conversationally).
Access
Refers to whether a program is available for disabled audiences. Captions make a program accessible to deaf and hard-of-hearing viewers. Descriptive narration makes a program accessible to blind and low-vision viewers.
Affiliate
An independently owned and operated local station which carries the programming of a major network and/or national programming service.
Analog
In electronics, a means of carrying an electrical signal by varying amplitude and frequency. The former standard for broadcasting television programs used an analog signal. The new standard uses a
digital signal.
ATSC
The
Advanced Television Systems Committee, Inc. is an international, non-profit membership organization developing voluntary standards for digital television, interactive systems and broadband multimedia communications.
Bandwidth
A measure of the information-carrying capacity of a communications channel; often expressed as a frequency range (such as megahertz) for an analog channel or as a data rate (such as megabits per second) for a digital channel.
Bits
Binary digits, "ones and zeros"; the fundamental units of information in a digital communications channel.
The world's first captioning agency, part of the
Media Access Group at WGBH.
Captioning
Like subtitles, captions display spoken dialogue as printed words on the television screen. Unlike subtitles, captions are specifically designed for deaf and hard-of-hearing viewers. Captions are carefully placed to identify speakers, on- and off-screen sound effects, music and laughter.
Closed Captioning
Closed captions are hidden as data within the television signal and they must be decoded to be displayed on your TV screen.
Compression
Any of several methods for reducing the bandwidth required for carrying a signal. Compression can be "lossy" (less important information is removed) or "lossless" (at the receiving end, the signal can be reconstituted as a bit-for-bit copy of the original).
Description
A generic term for the art of providing additional spoken detail describing key visual elements of an event or presentation, to provide increased access for audiences who are blind or visually impaired. Also known generically as "audio description", a service commonly provided in live theater, museums and a variety of community and educational settings. When applied to broadcast television and other visual media, the term "video description" is commonly used. The FCC uses "video description" in its proceedings, rulemakings and regulations.
Descriptive Video Service®
Descriptive Video Service® is a non-profit service of the WGBH Educational Foundation, and part of the
Media Access Group at WGBH. DVS® provides a supplemental audio service describing key visual elements of an audio-visual presentation for audiences who are blind or have low vision. Descriptive Video Service® and DVS® are registered trademarks of the WGBH Educational Foundation.
Digital
A method of representing information (for instance video, sound and other types of data) as a series of "ones and zeroes".
Distance Learning
The process of providing courses, lectures or other educational video via television signal over a geographically diverse area.
DTV
Refers to digital television broadcasts and to new televisions or set-top receivers/adaptors that can access and display digital broadcasts.
EIA-708B
The standard defining closed captioning for digital television systems, as defined by the Consumer Electronics Association (
CEA), and adopted by the Advanced Television Systems Committee (
ATSC).
Interactive
Pertaining to an information- or entertainment-distribution system in which the user is permitted to make choices or otherwise affect what is seen and heard.
MPEG-2
A video compression scheme created by the
Motion Picture Experts Group for delivering digital video for broadcast television and desktop computer environments.
Multimedia
Pertaining to an information- or entertainment-distribution system that includes text, audio and video in a computer-mediated format such that the user may interact with the various data types.
NCAM
Acronym for the
Carl and Ruth Shapiro Family National Center for Accessible Media at the WGBH Educational Foundation, the research and development area of the Media Access Division at WGBH in Boston.
Network
In broadcasting, a regional or national provider of programming to a number of geographically dispersed broadcast affiliates. In computers, a collection of software and hardware that allows physically separated computers to share data.
PBS
Abbreviation for the
Public Broadcasting System, a network of public television stations around the country. PBS was the first television network to serve deaf, hard-of-hearing, blind and visually impaired television viewers.
Vertical Blanking Interval (VBI)
The first 21 lines of a television field in the analog format, normally invisible to the viewer, where closed-caption data and other information are carried.
Boston's Public Broadcasting station, producer of programs such as Antiques Roadshow, Arthur, The American Experience and NOVA. Also a pioneer in media access technologies since 1972.
