Glossary Of Terms
AC-3: The 5.1-channel sound system specified in the Standard for Digital-HDTV. 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.
A/D: Analog to digital conversion. Used at transmission end of broadcast.
Addressable Resolution: The highest resolution signal that a TV or monitor can accept. It is important to note that while a particular device (Digital-HDTV) is able to receive the resolution, it may not be capable of displaying it.
Analog TV: Analog technology has been in use for the past 50 years to transmit conventional TV signals to consumers. "Standard" television broadcasts in analog TV. Analog signals vary continuously, creating 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: A numerical expression of the relationship of width to height of a TV screen. 4:3: This numerical sequence refers to the aspect ratio of the National Television Systems Committee (NTSC) TV screen, with "4" unit width corresponding to "3" unit height, proportionally, regardless of the actual size of the screen. 16:9: This numerical sequence refers to the aspect ratio of wide screen DTV formats for all HDTV and some SDTV (Standard Definition) video. A "16" unit width corresponds to "9" unit height proportionally, regardless of the actual size of the screen. The widescreen 16:9 numerical sequence provides a viewing experience very similar to that of 35 mm movies.
ATSC: An acronym for Advanced Television Systems Committee, which is responsible for developing and establishing Digital-HDTV Standards; and the name of the DTV system used by broadcasters in the U.S.
Bandwidth: A range of frequencies used to transmit such information 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.
Barn Doors: A term used in television production to describe the effect that occurs when a 4:3 image is viewed on a 16:9 screen. When this happens, viewers see black bars on the sides of the screen or "barn doors."
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.
Codec: This term is short for "Coder-decoder." A codec is a device that converts analog video and audio signals into a digital format for transmission. It also converts received digital signals back into an analog format.
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 three primary color signals: red, green, and blue that together convey all necessary picture information. With current consumer video products, the three 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 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.
Compression: Compression refers to the reduction of the size of digital data files by removing redundant and/or non-critical information ("data" being the elements of video, audio and other "information"). Digital TV in the U.S. would not be possible without compression.
Computer Input: Some HDTV sets have an input like SVGA or VGA that allows the TV sets to be connected to computers.
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.
Datacasting: Also known as "enhanced TV." Datacasting is the act of providing enhanced options offered with some digital programming to provide additional program material or non-program related resources. This allows viewers the ability to download data (video, audio, text, graphics, maps, services, etc.) to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.
Decoder: See "codec." A device or program that translates encoded data into its original format (i.e., it decodes the data.)
Digital: Digital refers to the circuitry in which data-carrying signals are restricted to one of two voltage levels, corresponding to logic 1 or 0.
Digital Cable: A service provided by many cable providers, digital cable offers viewers more channels. Contrary to many consumers' beliefs, digital cable is not the same as High-Definition Television or digital television; rather digital cable simply offers cable subscribers the options of paying for more services. Digital Monitor: DTV monitors are televisions that can display a digital signal but lack an integrated tuner (unlike an integrated digital set), and thus cannot receive a digital broadcast signal without an additional set-top box.
Digital Television (DTV): Digital TV is the umbrella term encompassing High-definition Television and several other applications, including Standard Definition Television, datacasting, multicasting and interactivity.
Digital Tuner: A digital tuner serves as the decoder required to receive and display digital broadcasts. It can be included inside TV sets or via a set-top box.
Dolby Digital: This is a digital surround sound technology used in movie theaters and upscale home theater systems that enhances audio. Home theater components with this technology work in conjunction with a "5.1-speaker" system (five speakers plus a low-frequency subwoofer) to produce true-to-life audio that draws the listener into the onscreen action.
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.
Down Converting: Process by which a high-definition signal is converted to a standard definition picture.
Enhanced TV: Also known as "datacasting." This term is used for certain digital on-air programming that includes additional resources downloaded to viewers. Some forms of enhanced TV allow live interaction; other forms are not visible on-screen until later recalled by viewers. Producers add these options to some digital programming to enhance program material -- allowing viewers the ability to download related program resources to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.
EDTV: This acronym stands for "Enhanced Definition Television." It refers to a complete products/system with at least a digital receiver display scanning format, and Dolby Surround Sound audio output capabilities.
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).
Generation Loss: This refers to video degradation caused by successive recordings (dubs of other dubs) from the master source. This is overcome by digital recording.
HDTV: "High-definition Television." This is the most superior video picture available in Digital TV. In the U.S., the 1080i and 720p formats in a 16:9 aspect ratio are the two acceptable HDTV formats. HDTV is a component of DTV.
Interactive Television: This is when TV programming features interactive content and enhancements, blending traditional TV viewing with the interactivity of a personal computer.
Interoperability: This refers to the ability of a system or a product to work with other systems or products without special effort on the part of the customer. For example, interoperability would be required for a digital television set to be plugged into a VCR that is plugged into cable with all the components working together.
Interlaced Scanning: This process divides and presents each video frame as two fields. Imagine a video frame being divided by the odd and even horizontal lines that make up the picture. The first field presents the odd lines; the second field represents the even lines. The fields are aligned and timed so that, with a still image, the human eye blends the two fields together and sees them as one. Motion in the image makes the fields noticeable. Interlace scanning allows only half the lines to be transmitted and presented at any given moment.
Letterbox: Letterbox refers to the image of a wide-screen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. It is used to maintain the original aspect ratio of the original source (usually a theatrical motion picture of 16:9 aspect ratio or wider).
Multicasting: The option to multicast was made possible by digital technology to allow each digital broadcast station to split its bit stream into 2, 3, 4 or more individual channels of programming and/or data services. (For example, on channel 7, you could watch 7-1, 7-2, 7-3 or 7-4.)
Must-carry: This refers to the legal obligation of cable companies to carry analog or digital signals of over-the-air local broadcasters.
NTSC: NTSC is the acronym that stands for National Television Systems Committee and the name of the current analog transmission standard used in the U.S., which the committee created in 1953.
Pixel: Pixel is actually two words jammed together � picture and element. A pixel is a tiny sample of video information, the "little squares" that make up an overall picture.
Pixels Per Inch: Pixels per inch (PPI) is a measure of the sharpness (that is, the density of illuminated points) on a television display screen.
Progressive Scanning: A system of video scanning where lines of a picture are displayed consecutively (unlike interlaced).
Resolution: The level of resolution directly affects picture quality. The higher the resolution, the more picture detail there is. Many things affect picture quality, including number of bits, pixel count, format, receiver quality, cameras, lenses and lighting used for live or taped programming. Resolution is measured by the number of pixels displayed. One of the high-definition picture formats is composed of 1080 active lines, and each line is composed of 1920 active pixels. Therefore, each frame has over 2 million (1080x1920=2,073,600) color pixels creating the image. By way of contrast, today's typical analog television is roughly equivalent to 480 active lines, with each line holding about 440 pixels. So, each frame has a little over 200,000 color pixels in use creating the image.
Sampling: This is the digital process by which analog information is measured, often millions of times per second, in order to convert analog to digital.
Standard Definition TV Format (SDTV): There are two main digital formats - HDTV and SDTV. SDTV typically does produce better quality images than that of traditional analog TV and pictures somewhat akin to digital cable. However, its images are not nearly as sharp as the images from the ultimate form of digital television � High-definition TV (HDTV).
Set-top Converter Box: This unit sits on top of the viewer's analog TV, receives the Digital TV signal, converts it to an analog signal, and then sends that signal on to the analog TV.
SVGA: This acronym is short for the "Super Video Graphics Array" display mode. SVGA resolution is 800 x 600 pixels.
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.
Terrestrial Broadcasting: This is a broadcast signal transmitted "over-the-air" to an antenna.
UHF: Ultra high frequency, the range used by TV channels 14 through 69.
Upconverting: Process by which a standard definition picture is changed to a simulated high-definition picture.
VGA: This acronym is short for the "Video Graphics Array" display mode. VGA resolution is 640 x 480 pixels.
VHF: Very high frequency, the range used by TV channels 2 through 13.
Wide screen: A term given to picture displays with a wider aspect ratio than NTSC 4:3. Digital HDTV or SDTV is referred to as "16:9 wide screen." Most motion pictures also have a 16:9 wide screen aspect ratio. Most Digital TVs have a screen that is wider than it is tall (if a Digital TV screen is nine inches high, it's 16 inches wide.) When watching a show recorded in the wide screen format on a Digital TV, viewers see more of the movie, while when viewing wide screen format on an analog TV, cropped edges are evident.
|
