The Language of High
Definition
Get ready for it! Digital television
is coming to a set near you sooner or later. Here's some of the vocabulary you'll need to
talk about it.
480i, 480p, 720p, 1060i: The names of the main forms
of digital television. The numbers refer to the number of scanning lines used to reproduce
the image -- 480 for regular television, 720 and 1080 for high-definition. The
"i" means the picture is interlaced. The "p" means it is scanned
progressively. See also "Progressive scanning" and "Interlace."
AC-3: The data-reduction scheme used in Dolby
Digital surround sound and, often in two-channel form, in digital television. Once widely
used as the overall name for Dolby Digital, although that's mostly disappeared.
Analog: The traditional method of recording and
broadcasting in which a continuously varying signal is recorded directly.
Aspect ratio: Image shape, expressed as the ratio of
picture width to height. Conventional television has a ratio of 4:3; high definition is
16:9. These are also expressed as 1.33:1 and 1.78:1.
Data reduction: A technique used to conserve data
storage space by removing inaudible material from audio signals or redundant matter from
video ones. Also called perceptual coding or, less accurately, digital compression.
Digital: Video or audio that has been converted to
binary digits which can be manipulated, stored, and transmitted before being
returned to their original analog state.
Digital television (DTV): A method of either putting
a potentially immense signal, such as HDTV, on a conventional TV channel, or cramming
several normal-quality signals into the same space.
Dolby Digital 5.1: A 5.1-channel digital surround
system. Available on some HDTV broadcasts, primarily of movies.
DTS 5.1: A competing 5.1-channel system. It’s
incompatible with Dolby Digital but essentially identical in audio effect.
HD-ready: A television set that can display
high-definition images, but has to get its digital signal from an external tuner or
satellite box.
HDTV: High-definition television, the original
justification for the digital-television standard, but now just one of its possible
applications. It features film-like images and a widescreen format.
Interlace: The practice of "painting" a
video image by producing first the odd-numbered scan lines, then dropping the even ones
between them. See also "Progressive scanning."
Perceptual coding: See "Data reduction."
Progressive scanning: The technique of producing all
the lines of a video image in order, rather than interlacing them.
SDTV: Standard-definition television. See
"480i."
...Ian G. Masters
ian@mastersonaudio.com
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