Glossary of TV Terms
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AC Alternating Current. Australia has 240 volts alternating at 50 cycles per second (Hz).
Active Picture Area The part of a TV picture that contains actual image information as opposed to sync or other data. Vertically the active picture area is 486 lines for NTSC and 576 lines for PAL. The inactive area is called blanking.
Analogue A signal that varies continuously over a range of amplitudes. A digital signal by contrast has only two values, representing 1 or 0. Analogue is transmitted at 7Mhz in VHF/UHF PAL B/G
Aspect Ratio Refers to the shape of a TV screen. The traditional TV screen that is nearly square has a ratio of 4:3. The widescreen format has a ratio of 16:9, which approximates the proportions of actual movie theatre screens. This also refers to the size of the picture, irrespective of the screen size.
1.33:1 (4:3) aspect ratio is the traditional TV size also known as Full Frame.
1.66:1 aspect ratio is seldom used It's a compromise between 1.33:1 and 1.85:1 ratios.
1.78:1 (16:9 or Anamorphic Widescreen) is the aspect ratio used on widescreen TV's. This is the midpoint between 4:3 and Panavision (detailed below). It is a compromise to achieve a full screen most of the time. This ratio is used in the new digital TV format in Australia.
Panavision 1.85:1 aspect ratio is commonly used in movie theatres and on many DVD's.
Panavision 2.35:1 and 2.40:1 aspect ratios provide a very wide, panoramic image, hence the name Panavision, which was established in the early 70's. Many films are shot in this format as it was compatible with most movie theatres.
Cinerama 2.77:1 and 3.00:1 aspect ratio produces thick bars top and bottom - even on a widescreen television. Three cameras were used to capture the film, and the films were then stuck together to form one print. This is why they are so wide. This format looked fantastic in the cinema, and really blew audiences away, however on TV's it can appear only 10cm tall.
Auto Programming Set top boxes will automatically scan all available channels to find the ones transmitting in your area. This needs to be done once you plug the unit in. For twin tuner models, BOTH tuners need to be tuned in.B
Bandwidth The amount of audio or radio spectrum required or used by a signal or waveform.
BNC connector A connector with a bayonet lock used with coaxial video cable.
Brightness control A control used to adjust the illumination of viewfinders, monitors, and receivers, but not affecting signal levels from cameras or other picture sources.
Burn In When stationary graphics are onscreen for long periods of time, the continuous image can "burn" into the screen, resulting in a ghostly after-image superimposed over anything you watch. This is most common on rear projection sets and some plasmas and LCD displays. This can be minimised by not leaving your television on when not watching it, and watching a combination of widescreen and 4:3 material.C
Cable The electrical cords used to interconnect pieces of audio and video equipment.
Cell Gap The space containing the liquid crystal in a LCD display. The liquid crystal is sandwiched between two plates of glass.
Chroma The characteristic of a color which refers to its saturation or intensity.
Chrominance The color portion of the television signal.
Chrominance signal or chroma signal is a video signal containing color information.
Coaxial cable A cable having a center conductor surrounded by insulation and a grounded shield. Used for antenna installations, and also to connect your wall plate to your set top box. Common variants are RG6 and RG59.
Color bar signal is a test signal which can be displayed as vertical bars of different colors on a color video monitor. It is used to check chrominance functions of color television and camera's.
Component video signal A signal that consists of a luminance signal (Y) and two chrominance (color difference) signals (R-Y, B-Y).
Composite video signal A signal that consists of video (luminance and color sub carrier), sync (horizontal and vertical), and color burst signals.
CRT Cathode-ray tube A conventional television set.
CTDM Compressed Time Division Multiplex A method of processing chrominance signals for recording. When component video signals are recorded, both of the two chrominance signals (R—Y, B—Y) are time-compressed to half, multiplexed, and recorded on a single track one after the other.D
Datacasting Digital television allows for the transmission of not only digital sound and images, but also digital data (text, graphics, maps, polls, etc.). This aspect is the least developed; but in the near future, applications will likely include interactive program guides, sports statistics (seen on channel 7 broadcasting of the Rugby World Cup), stock quotes, retail ordering information, and the like. Datacasting is currently not two-way, although most industry experts expect that more set-top box manufacturers will create methods for interaction. By integrating dial-up Internet connections or ethernet with the technology, simple responses will be possible using a modem/home network and either an add-on keyboard or the set top box remote control.
dB Decibel. A unit used to compare the relative levels of electrical signals on a logarithmic scale.
Digital Coax Out Transmits a digital audio signal via a digital coaxial cable. Similar in quality to a digital optical output. Similar in quality to a digital optical output, but more prone to interference as it is an electrical signal, where as optical outputs use light instead.
Digital Optical Out Transmits a digital audio signal via an optical cable. A very clean way of delivering audio to a digital amplifier.
Digital Television (DTV) Transmission of signal by encoding it as 0s and 1s just like in computers. DTV can be compressed to provide more channels in the same bandwidth required for one channel of the current standard television, better sound, and more picture information (more detail) than conventional television.
Distortion Any undesirable alteration in an audio or video signal.
Dolby Digital 5.1 channel audio standard for digital television. Six distinct audio channels are used: left, center, right, left rear, right rear and a sub woofer indicated by the .1.
Downconverting is a process by which a high-definition signal is converted to a standard-definition picture. You need a High Definition receiver for this purpose. There is a signal degradation in the downconversion process.
DVD Digital Video Disk (or Digital Versatile Disk). A format for putting full length movies on a 5" CD using MPEG-2 compression for "much better than VHS" quality.
DVI Digital Video Interface. A specification of connector, like SCART, created by Digital Display Working Group. It is a uniform connector that can carry both digital and analogue video and audio signals. There are 31 pins on a DVI connector. There are three different versions:
DVI - A Digital Video Interface Analogue - for analogue signals
DVI - D Digital Video Interface Digital - for digital signals
DVI - I Digital Video Interface Integrated - for a combination of analogue and digital signals.E
Effective Area The viewing area of a plasma or LCD display, also used for computer monitors and televisions.
Electronic Program Guide (EPG) An application that provides an on-screen listing of all programming and content for that channel. Typically lists what is on Now and Next.F
Field One scan from the top to the bottom of the television frame, tracing alternate horizontal lines and taking one sixtieth of a second to complete.
Frame A complete television picture consisting of two interlaced fields of video. The frame rate for PAL system is 24 frames per second and for the NTSC system is 30 frames per second.
Freeze frame The continuous repetition of a single frame of video some set top boxes have freeze frame, or pause buttons on the remote.
Frequency The rate of repetition of an electrical or audio signal, expressed in Hertz (cycles per second).
Fuse A device designed to interrupt an electrical circuit in the event of an overload of that circuit.G
Gain Degree of amplification. The difference between the signal level at the input of a device and the level at the output, usually expressed in dB.H
HDTV High Definition Television A TV format capable of displaying on a wider screen (16x9 as opposed to the conventional 4x3) and at higher resolution.
Hertz Cycles per second.
Horizontal resolution The capability of a display unit to resolve detail in the horizontal direction. Usually expressed as the number of vertical lines which can be distinguished in the reproduced image of a test chart.
Horizontal sync That portion of the sync signal that controls the horizontal timing (and therefore horizontal location) of each line of picture.
Hum Unwanted low frequency audio noise caused by improperly shielded or improperly grounded audio cables and circuits.I
iDTV Integrated Digital Television. This is a television with an in built digital tuner, if you have one of these you don't need a set top box.
Interactive Television (ITV) TV programming that features interactive content and enhancements, blending traditional TV viewing with the interactivity of a personal computer (not commonly available at this time except for some TEAC boxes).
Interlaced The means by which televisions create images. An interlaced-scanning tube sends information to each pixel in the even-numbered rows of pixels on a screen, left to right and top to bottom. Then it sends information to odd-numbered rows. This results in a slightly distorted picture, as the entire image doesn't appear at once. The 1080i (interlaced) high definition standard is an interlaced-scanning standard. See here for more info.
Internal sync Synchronizing signals generated by a camera, recorder, or other picture source without reference to or need of external synchronizing signals.
I signal One of the two color signals, containing reddish orange and bluish green components to which the human eye is sensitive.K
Keystone The effect of projecting an image onto a surface that is not perpendicular to the axis of the projecting lens. Parallel lines tend to converge in the direction where the surface is closer to the lens. Some new projectors have in built circuits to minimise or eliminate this.L
Lag The tendency in some camera pickup tubes to retain an image after it is no longer presented to the tube. This effect is most evident when a relatively bright image is replaced by a darker field of view and is aggravated when a bright image is stationary in the field of view for an extended period of time before it is replaced.
LCD (Liquid Crystal Display) LCD allows screens to be thinner, and televisions lighter and more energy efficient. The result is television that can fit flat on a wall and doesn't generate as much waste heat. When voltage is applied to liquid crystal molecules that are sandwiched between two panes of glass, molecules that are arranged horizontally to the panels begin to rearrange themselves vertically. When light is emitted from one of the panels, it passes through the vertically arranged liquid crystal molecules, and reaches the other panel, which lets the light pass through. This is like light shining into a room from the top of a set of blinds. When the slats are open, you can see through the blinds and see the sunlight on the floor. However, when the slats are raised, light is blocked and the floor becomes dark.
Letterbox Refers to the image of a widescreen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. It is used to maintain the aspect ratio of the original source (usually a movie 16:9 aspect ratio or wider). You will see more and more of this even on analogue services as digital becomes more common.
Logical channel numbering This is typically set so that 2=ABC, 3=SBS, 7=7, 9=9 and 1=10 irrespective of the actual channel assigned to the broadcaster in your area.
Luminance signal A signal that determines the brightness of the picture. Also called Y signal.M
MPEG-2 is a compression standard for picture and sound set by the Motion Pictures Expert Group (MPEG). MPEG-2 is the basis for Australian Digital Television transmissions. It carries up to 8 channels of audio.
Multicasting The ability to send more than one channel of programming within the allotted channel spectrum. While analog channels have traditionally used a standard amount of spectrum (represented by each click on your tuner dial), digital channels can fit more channels into their spectrum. This is illustrated by channel 10 running both a standard definition channel and a high definition channel, as well as 10 Digital1, 10 Digital2, etc.N
Noise Any unwanted signal interfering with the clarity and intelligibility of desired signals. The background of static inherent in any recording or amplifying device, generally forty to sixty db below the peak output level of the device.O P
PAL Phase Alternate Line The television and video standard in used in Australia and most of Europe. Consists of 625 horizontal lines at a field rate of 50 fields per second. (Two fields equals one complete Frame).
PAL (Phase AlternatING Line) Video Standard, 625 scan lines (Only 576 of these lines are used for picture. The rest are used for sync or extra information such as VITC and Closed Captioning), tape runs at 25 frames per second.
Pan and Scan When a movie is cropped from its original theatrical aspect ratio (generally 16:9) to fit a 4:3 TV.
Phosphors Phosphors are the material on back glass that emit the visible light that makes up the picture we see. On a normal TV the phosphors are on the front glass and are excited by a beam of light from the cathode ray. In all flat and plasma TVs the phosphors are excited by UV light produced by electromagnetically charged plasma.
Pixel Short for Picture Element. The basic unit from which a video or computer picture is made. Essentially a dot with a given color and brightness value. The more pixels the higher the resolution of the picture.
Plasma An electronically neutral, highly ionized substance composed of ions, electrons and neutral particles. Plasma contains almost equal numbers of free electrons and positive ions. In a plasma the electrons have been stripped away from the central nucleus. Therefore, a plasma consists of a sea of ions and electrons and is a very good conductor of electricity and is affected by magnetic fields. Electrons are separated from their respective nucleus when enough heat is applied. When this happens, light is emitted. This happens billions of times per second to create a picture.
Plasma Display Plasma technology is different from that used in other display systems in that red, green and blue lights are created in every pixel, making packaging tighter and more efficient. Charged electrodes between glass panels cause tiny pockets of inert gas to change the state of the plasma. This process causes UV light to be produced, which in turn reacts with the red, green and blue phosphors in each pixel to produce visible light.
Progressive Scan The system used by picture tubes of Plasma displays, LCD displays, computer monitors and newer televisions to display pictures. The process uses a progressive scanning tube to send information to each pixel on a screen one after another from the top left to the bottom right all in one pass. The 720p (progressive) high-definition standard is a progressive-scanning standard. Progressive scan offers higher-quality pictures than does interlaced scan. See here fore more info
PVR Personal Video Recorder - in digital set top box speak, this means the box has a hard disk in it that allows you to record digital television broadcasts. It is also another old term for VCR.Q
Q signal One of the two color signals, containing yellow and violet components to which the human eye is relatively insensitive.R
RCA See this page.
Receiver Any device capable of demodulating an RF signal, such as a digital set top box, radio, tuner, or television set.
Reference video signal A video signal which contains a sync signal or sync and burst signals, used as a reference for synchronization of video equipment.
Resolution The amount of data used to make up a picture, screen, or audio track. The more data in a picture, the richer the image and the higher the resolution. Also the degree to which fine detail can be recorded or displayed. In film, measured in pairs of light and dark lines per millimeter. In television, measured in lines per scan. Thus, the horizontal resolution of a television would be measured by the number of discernible vertical lines that could be displayed across the width of the screen.
RF (Radio Frequency) That part of the frequency spectrum in which it is possible to radiate (transmit) electromagnetic waves. Any part of the broadcast band, including radio and television.
RGB Red, Green, Blue The primary colors of light. Computers and some analog component devices use separate red, green, and blue color channels to keep the full bandwidth and therefore the highest quality picture. See this page.
RGBHV This format is the domain of plasma screens and LCD's mostly in an home theatre environment. We've been using these signals in a PC environment for years though. It is similar to RGB, but the HV at the end means that the synchronisation (timing) pulses are on separate wires, one for horizontal and one for vertical.
R—V signal R (red) signal minus Y (luminance) signal; one of the color difference signals.S
Safe area In television graphics or film shot for television, the area which is almost certain to be displayed on any television set. About 80% of the scanned area.
SECAM (Systèm Electronique pour Couleur avec Mémoire) Video Format at 625 scan lines, tape runs at 25 frames per second.
Set Top Box A digital television decoder used to display digital pictures on an analogue television.
Simulcasting This is commonly used to mean the simultaneous transmission of digital and analogue signals. Analogue will be phased out after 2008 according to the government.
S/N Signal-to-Noise ratio The relation of the strength of the desired signal to the accompanying electronic interference, the noise. If S/N is high, sounds are reproduced with less noise and pictures are reproduced clearly without snow.
SVHS or Y/C or . See this page.
Sync Any of the signals used to generate and control a television picture, but, specifically, the portion of the composite video signal from zero to minus forty IRE units consisting of vertical and horizontal timing pulses and equalizing signals to maintain the proper relationship of the two fields of video making up each frame.T
Terrestrial This refers to terrestrial broadcasting, where the signal is sent from a ground based transmitter. This is in contrast to satellite television, which is sent from an orbiting transmitter located in the Clarke Belt, an area that keeps satellites geostationary.
Time code A digitally encoded signal that is recorded on videotape to identify each frame of video by hour, minute, second and frame number. SMPTE time code is applied to NTSC system, and EBU time code to PAL and SECAM systems. There are two kinds of recorded signal: longitudinal time code (LTC) and vertical interval time code (VITC). See also LTC and VITC.
Tuner The demodulator section of a radio, television set, or videotape recorder.
Twin Tuner A set top box with two tuners inside. This allows you to receive two channels at once. Doing this allows functions like Picture in Picture (PIP) and simultaneous recording of one channel while watching another. Some units will allow you to record two channels at once.U
UHF Ultra High Frequency. Radio frequencies from 300 to 3,000 megahertz.
Upconverting Where a Standard Definition picture is converted to a simulated High Definition picture. This is nowhere near as good as a true High Definition image.V
Variable Audio Output Most boxes on the market have volume controls, and this adjusts the level of the RCA outputs to your stereo or TV and even your Digital amplifier.
VHF Very high frequency. Radio frequencies from 30 to 300 megahertz.
Video gain Amount of amplification for video signals, expressed in decibels (dB)
VTR Videotape recorder. Same as VCR - Video Cassette Recorder.W
Widescreen A reference to the proportions of a television screen. Widescreen displays 16 horizontal units for every 9 vertical units. A conventional display is 4 units horizontally by 3 vertical units, or almost square.X Y
Y/C or S-VHS See this page.Z