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Digital Glossary

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 DD5.1 audio.

Advanced Television Systems Committee (ATSC)
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.

Addressable Resolution
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
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 digital pictures.

Aspect Ratio
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 channel.

Bit Rate
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.

Composite Video
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 (HDTV)
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).

Interlaced Scanning
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.

Line Doubling
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 source.

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.

Pillarbox 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 area.

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.

Progressive Scanning
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.

Set-top Box
(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 displayable picture.

A range of frequencies available for over-the-air transmission.

Standard Definition Television (SDTV)
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.

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 at vidiot.com