AC-3
Also known as Dolby Digital, AC-3 delivers CD-quality digital audio and provides five full-bandwidth channels for front left, front right, center, surround left and surround right speakers, plus an LFE (low frequency effect) subwoofer, for a total of 5.1 channels.

Advanced Television Systems Committee
Also known as ATSC, the committee responsible for digital television standards and development, as well as all 18 formats of DTV.

A/D
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. The device, however, may not be capable of displaying this resolution.

Analog TV
"Standard" television broadcasts analog TV. Analog signals vary continuously, representing fluctuations in color and brightness.

Artifacts
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.

ATSC
See Advanced Television Systems Committee.

ATV
"Advanced Television" is an earlier term used to describe the development and advance applications of digital television, now simply referred to as DTV.

Bandwidth
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.

Channel
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 (P_P, P_R), 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).

Compression
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.
D/A
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.

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).

DTS
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.

Downconvert
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.

EPG
Electronic program guide. An on-screen display of channels and program data.
Frequency
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 5.1 independent channels of CD-quality stereo surround sound, (also referred to as 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.

Letterbox
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.

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.

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.

Resolution
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.

Set-top Box (DTV STB)
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 and provide a displayable picture.

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

Standard Definition Television (SDTV)
Digitally transmitted SDTV includes 480 line resolution in both interlaced and progressively scanned formats. It offers significant improvement over today's conventional NTSC picture resolution, and is similar to DVD or DBS quality because the digital transmission eliminates snow and ghosts, which can be common with the current NTSC TV format. Also, thanks to digital compression technology, several programs can be transmitted simultaneously within the same channel.

S-Video
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.

UHF
Ultra high frequency, the range used by TV channels 14 through 69.

Upconvert
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.
VHF
Very high frequency, the range used by TV channels 2 through 13.

Y, P_B, P_R
Generally used where a digital TV signal source is employed. The video signal is separated into its component parts of brightness and color differentials. The most advanced method for interconnecting decoded video data.

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.


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