As you gather information
about Digital-HDTV, you will likely come across
some terminology that is alien. Here's a brief
Digital-HDTV Glossary to help you with some
common "tech-speak" terms...
While analog TV has MTS 2-channel audio (basically
FM stereo over your TV), the ATSC DTV standard
uses AC-3 digital audio, otherwise known as
Dolby Digital. It is the same digital audio
that is found on DVDs and in movie theaters.
The AC-3 format provides for audio as simple
as a single audio channel (DD1.0), up through
five channels [left, center, right, surround
left and surround right] as well as a subwoofer
channel (DD5.1). DTV programming will either
be DD2.0 (even if mono) or DD5.1. To use any
of the other formats would make it extremely
difficult, and expensive, for TV stations to
handle. Dolby Surround (otherwise incorrectly
known as Dolby Prologic II) is provided for
in the DD2.0 format. There is a bit that is
set in the DD2.0 audio that indicates that there
is Dolby Surround phase audio in the audio stream.
Most audio devices that handle Dolby Digital
audio will automatically go into Dolby Surround
mode, using the Dolby Prologic II circuitry.
The quality of the audio can be as good as CD,
or even better, since Dolby Digital uses a 48
KHz sampling rate, compared to the CD standard's
44.1 kHz. For AC-3, the quality is also affected
by the compression rate. So far 384 kbps is
used for DD2.0. Fox uses 448 kbps for their
Advanced Television Systems
The ATSC is the committee responsible for developing
and establishing Digital-HDTV Standards; as
well as all (18) formats of Digital TV.
Analog to digital conversion (or converter).
Used at transmission end of broadcast.
The highest resolution signal that a display
device (TV or monitor) can accept. Caution:
Consumers should be aware however, that although
a particular device (Digital-HDTV) is able to
receive the resolution, it may not be capable
of displaying it.
Analog TV is the NTSC Standard for traditional
television broadcasts. Analog signals vary continuously,
representing fluctuations in color and brightness.
Unwanted visible effects in the picture created
by disturbances in the transmission or image
processing, such as 'edge crawl' or 'hanging
dots' in analog pictures, or 'pixelation' in
Refers to the width of a picture relative to
its height. If an NTSC picture is 4 feet wide,
it will be 3 feet high; thus it has a 4:3 aspect
ratio. HDTV has a 16:9 aspect ratio.
See Advanced Television Systems Committee.
"Advanced Television" is an earlier
term used to describe the development and advance
applications of digital television, now simply
referred to as DTV.
A range of frequencies used to transmit information
such as picture and sound. For TV broadcasters,
the FCC has allocated 6Mhz for each channel.
For DTV, the maximum bit rate possible within
the bandwidth is 19.4 Mbps, which is one HDTV
channel. SDTV has a lower bit rate, therefore
the bandwidth can accommodate more than one
Measured as "bits per second," and
used to express the rate at which data is transmitted
or processed. The higher the bit rate, the more
data that is processed and, typically, the higher
the picture resolution.
A 6 Mhz (bandwidth) section of broadcasting
spectrum allocated for one analog NTSC transmission.
Component Video Connection
The output of a video device (such as a DTV
set-top box), or the input of a DTV receiver
or monitor consisting of 3 primary color signals:
red, green, and blue that together convey all
necessary picture information. With current
consumer video products, the 3 component signals
have been translated into luminance (Y) and
two color difference signals (PP, PR), each
on a separate wire.
An analog, encoded video signal (such as NTSC)
that includes vertical and horizontal synchronizing
information. Since both luminance (brightness)
and chrominance (color) signals are encoded
together, only a single connection wire is needed
(i.e. RCA cables).
A method of electronically reducing the number
of bits required to store or transmit data within
a specified time or space. The video industry
uses several types of compression methods but
the method adopted for DTV is called "MPEG2."
Four full-range channels of programming and
data can be compressd into the same space required
by a single analog channel.
Conversion of digital to analog signals. The
device is also referred to as DAC (D/A converter).
In order for conventional television technology
to display digitally transmitted TV data, the
data must be decoded first and then converted
back to an analog signal.
Abbreviation of "Digital Broadcast Satellite"
- refers to digital TV transmissions via satllite.
Digital Television (DTV) Refers to all formats
of digital television, including high definition
television (HDTV), and standard definition television
(SDTV). Also referred to as ATV (Advanced TV).
Digital Theater Systems sound. Discrete 5.1
channel surround system similar but not the
same as Dolby Digital. Dolby Digital is the
DTV standard, but DTS competes with it on DVD
and in the movie theaters.
A term used to describe the format conversion
from a higher resolution input signal number
to a lower display number, such as 1080i input
to 480i display.
Electronic program guide. An on-screen display
of channels and program data.
The number of times per second that a signal
fluctuates. The international unit for frequency
is the hertz (Hz). One thousand hertz equals
1 KHz (kilohertz). One million hertz equals
1 MHz (megahertz). One billion hertz equals
1 GHz (gigahertz). Television is broadcast in
frequencies ranging from 54 MHz to 216 MHz (VHF)
and 470 MHz to 806 MHz (UHF).
High Definition Television
The generally agreed upon definition of HDTV
is approximately twice the vertical and horizontal
picture resolution of today's NTSC TV, which
essentially makes the picture twice as sharp.
HDTV also has a screen ratio of 16:9 as compared
with most of today's TV screens, which have
a screen ratio of 4:3. HDTV offers reduced motion
artifacts (i.e. ghosting, dot crawl), and offers
up to 5.1 independent channels of CD-quality
stereo surround sound. (see AC-3).
In a television display, interlaced scanning
refers to the process of re-assembling a picture
from a series of electrical (video) signals.
The "standard" NTSC system uses 525
scanning lines to create a picture (frame).
The frame/picture is made up of two fields:
The first field has 262.5 odd lines (1,3,5...)
and the second field has 262.5 even lines (2,4,6...).
The odd lines are scanned (or painted on the
screen) in 1/60th of a second and the even lines
follow in the next 1/60th of a second. This
presents an entire frame/picture of 525 lines
in 1/30th of a second.
The term used to describe the way a 16:9 aspect
ratio image is displayed on a 4:3 screen, where
black areas are visible above and below the
image. HDTV programming can also have letterboxing.
If a standard movie is shown, the 1.85:1 aspect
ratio will have very slim horizontal letterbox
bars on the top and bottom (4:3 is also described
as 1.78:1). But, when a 2.35:1 movie is shown,
the image will be letterboxed. The letterboxing
of a 2.35:1 on a 16:9 screen is a lot less than
on a 4:3 screen.
A method, through special circuitry, to modify
an NTSC interlaced picture to create an effect
similar to a progressively scanned picture.
The first field of 262.5 odd-numbered lines
is stored in digital memory and combined with
the even-numbered lines. Then all 525 lines
are scanned in 1/30th of a second. The result
is improved detail enhancement from an NTSC
National Television Standards Committee responsible
for developing Standards for "traditional"
Analog TV, prior to Digital-HDTV.
"Phase Alternation Line" - A signal
format used in video equipment in Europe and
parts of Asia. PAL signals give you 25 frames
per second, and so are incompatible with NTSC,
the American video signal format.
Even though HDTV has an aspect ratio of 16:9,
not all programming is available in 16:9. In
order for the old 4:3 aspect ratio to be displayed
within a 16:9 window, pillar bars, or vertical
bars of some color (normally black), are placed
on the left and right of the 4:3 image, in order
to center it and fill in the remaining 16:9
Term used for "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 less than half a million pixels. The
pixel count for HDTV is nearly two million.
In progressive scanning, typically used by VGA
computer monitors, all the horizontal scan lines
are 'painted' on the screen at one time. Adopted
DTV formats include both interlaced and progressive
broadcast and display methods.
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, called pixel density.
SECAM (Système Electronique Couleur Avec Mémoire)
is a signal format used in video equipment in
France and the former Soviet Union. It is incompatible
with PAL and NTSC formats.
(STB)(also: Decoder, Receiver, Tuner) A unit
similar to today's cable boxes, which is capable
of receiving and decoding DTV broadcasts. A
DTV 'Certified' STB can receive all (18) ATSC
DTV formats, (including HDTV) and provide a
A range of frequencies available for over-the-air
Standard Definition Television
SDTV refers to DIGITAL transmissions with 480-line
resolution, either interlaced or progressive
scanned formats. SDTV offers significant improvement
over today's conventional NTSC picture resolution,
similar to comparing DVD quality to VHS, primarily
because the digital transmission eliminates
snow and ghosts, common with the current NTSC
analog format. However, SDTV does not come close
to HDTV in visual quality. SDTV audio is DD2.0.
Separated video. An encoded video signal which
separates the brightness from color data. S-video
can greatly improve the picture when connecting
TVs to any high quality video source such as
digital broadcast satellite (DBS) and DVDs.
Ultra high frequency, the range used by TV channels
14 through 69.
The term used to describe the conversion of
a lower apparent resolution to a higher number,
such as "upconverting" 720p to 1080i.
This is a misnomer, though, since to accomplish
this, the horizontal scanning frequency is actually
lowered from 45kHz to 33.75kHz. Resolution quality
is not improved by this method.
Very high frequency, the range used by TV channels
2 through 13.
Y, PB, PR
The most advanced method for interconnecting
decoded video data. Generally used where a digital
TV signal source is used. Preferred connection
for High Definition TV signals; enables superior
quality in transmitted picture. The video signal
is separated into its component parts of brightness
and color differentials.
Y, U, V
Also sometimes referred to as Y, Cr, Cb, where
a video signal is separated into components
of brightness and color, arguably to a degree
more advanced than S-video.
Special thanks to Mike Brown