HDTV is a complicated, technical business that can be very confusing at best and at worst indecipherable. That is why we have put together this handy HD jargon buster - an extensive high def glossary of all the technical terms you may come across, with explanations in plain old English.

AC-3
The industry standard sound system HDTV. Known also as Dolby Digital Surround. AC-3 delivers CD quality digital audio, providing a total of 5.1 channels played through five speakers - front right, front left, centre, surround right and surround left not forgetting one LFE (low-frequency effect) subwoofer.

Advanced Television Systems Committee (ATSC)
The committee responsible for the development of HDTV Standards in addition to all other DTV formats.

A/D Analog to digital converter or conversion.

Analogue TV
Analogue TV is being replaced by Digital TV. For our purposes we refer to analogue TV this in the guide as old style or traditional TV.

Artifacts
Artifacts are picture imperfections caused by transmission interference. Analogue TV suffered from ghosting or a snowy image while digital television could suffer from pixellation or garbage information.

Aspect Ratio This refers to the relative width and height of a picture. Analogue TV has an aspect ratio of 4:3. HDTV has an aspect ration of 16:9 which is the same as wide-screen.

Bandwidth
A range of frequencies used to transmit information over the HDTV uses considerably more bandwidth than DTV.

Bit Rate
Bits per second used to measure the rate at which data is transmitted or processed. Generally speaking the higher the bit rate the better the picture and sound quality.

Brightness
Expressed as candelas per square metre (cd/m2) brightness tells us how much light is emitted from the screen. A higher candela signifies a brighter picture.

Channel
A single section of bandwidth from the broadcasting spectrum allocated for one analog NTSC transmission.

Component Video A digital connection composing of three separate leads joined into one - Red, Green and Blue used to transmit both video and audio information.

Composite Video Not to be confused with component video, composite video is an analogue signal used in the broadcast of analogue television. It carries picture information only with colour and brightness signals composited into a single lead..

Compression Digital signals can be compressed to reduce the amount of bandwidth needed to broadcast them. MPEG-2 has been specified as the industry standard and can produce pictures ranging from VHS to HDTV quality. Four DTV channels can be compressed into the space of a single analogue channel. A single full-range channel of HDTV will take up the same space.

Contrast Ratio
Contrast ratio is a comparison of a display screens capability to reach extremes of whites and black. The higher the contrast ratio, the richer the on-screen colours. Contrast ratio is often overlooked in favour of resolution but it is a crucial factor in determining picture quality

D/A Digital to analogue conversion. Digital set top boxes such as freeview can perform this conversion to allow DTV to be watched on standard analogue TV sets. Some boxes can do the same with HDTV but the quality will be severely compromised after the conversion.

DBS
Is an abbreviation of the term Digital Broadcast Satellite - referring to DTV satellite transmissions.

DLP
Digital light processing is a microdisplay technology invented by Texas Instruments. DLP is founded on a digital micromirror device (DMD). This is a chip with millions of microscopic mirrors attached by hinges, each micromirror corresponding to an individual pixel in the image. Red, green, and blue light is filtered through a colour wheel and directed onto the DMD, which alternates switching on and off at a rate of up to 5,000 times per second. The light reflected from the DMD passes through a lens and onto the screen thereby creating an image. Top of the range HDTV projectors dispense with the colour wheel using instead three DMD chips - one each for green, red, and blue..

Dolby Digital
Six channel digital audio specified as industry standard for HDTV, sometimes know as Dolby 5.1 Surround Sound or AC-3. It is intended to be played through an audio set-up comprising of 5 speakers - front left, front right, front center, surround or rear left, surround or rear right and a subwoofer..

Downconvert
In DTV a higher resolution input signal can be converted to lower one. Some DTV receivers can downconvert an 1080i HDTV signal to a standard 480i one allowing it to be viewed on a TV that is not HDTV ready. Loss in quality occurs.

DTS
Digital Theater Systems sound. A 5.1 channel surround sound system much like Dolby Digital.

DTV
Digital television. A generic term that refers to all digital television formats, including high definition television (HDTV) and standard-definition television (DTV).

DVI
Digital Visual Interface. A digital connection designed for computers that carries high-bandwidth video information only. It is being largely replaced by the HD ready compliant HDMI socket but may still be found on many HD devices.

D-VHS
Digital-VHS. A digital version of the VHS (Video Home System) videocassette designed to record HDTV via a Fire-wire connection.

DVR
Digital video recorder. A new type of television recording device that stores data on a hard disk rather than portable media such as VHS cassettes DVDs. Benefits of this device include advance functions allowing you to record and replay entire programme seasons, the availability of an EPG or Electronic Program Guide, the ability to watch one program while recording another and even the ability to pause live TV. There are both DTV and HDTV DVRs available, optional extras may include the ability to write DVDs from its memory. It is also known as a PVR - personal video recorder or hard disk recorder.

EPG
Electronic program guide. An handy on screen display of available channels and program information.

High Definition Television (HDTV)
The generally agreed upon industry standard for HDTV is a signal with a picture resolution around twice size of analogue PAL TV. The picture ratio is of 16:9 as compared with 4:3 analogue. HDTV offers 5.1 Dolby digital surround sound and enhanced picture quality with reduced interference.

HDCP
High-bandwidth Digital Content Protection. This is an Intel developed copy protection scheme developed designed to be used in conjunction with HDMI and DVI connections. It is included in the HD ready standard.

HDMI
High-Definition Multimedia Interface. A digital video connection somewhat akin to USB and designed to replace DVI which it improves upon by being able to carry both audio and video data in a single connection.

HD DVD
High Definition Digital Versatile Disc. HD DVD was intended to be the high definition successor to standard DVD but has since found itself in a format war with Sony’s Blu-ray. The discs can store more than three times as much data as standard DVDs with 15 GB per layer compared to the old 4.7 GB.

IEEE 1394 (FireWire)
A digital interface initiated by Apple and developed by the IEEE 1394 working group. Also known by Sony as i.Link. Transports data at high speeds of 100, 200, or 400 Mbps. FireWire can be used to connect digital television devices where the port is available.

Interactive television :
The television and entertainment industry in general hope to bring an increasingly interactive element to our TV watching habits. DTV being a digital broadcast where data can be sent both ways, is paving the way for such an event. In addition both Blu-ray and HD DVD technologies allow for interactive features and programming languages to be installed that go way beyond the scope of standard DVD or VHS systems.

Interlaced Scanning
Interlaced scanning refers to the process of re-assembling a picture from a series of electrical (video) signals.

IPTV
Internet Protocol Television is a system where digital television service is delivered over the internet this may be delivered by broadband.

ISDN
Integrated Services Digital Network. This enables high-speed data transmission over a telephone network. ISDN can vary from a basic rate of 64 Kbits per second right up to a primary rate of 2 Mbps.

Liquid Crystal Display An LCD television or monitor uses liquid crystals to act as shutters within the TV screen. Thousands of tiny light sources at the rear of the display act on a layer of liquid crystals cells. As an individual liquid crystal cells is electrified with current, the crystals align and stop light from shining through, or conversely the crystals scatter allowing the light to shine through and this process forms a moving image on the screen. LCD screens usually only display progressive scan format. Compared to Plasma screens LCDs do not use phosphors and are therefore not susceptible to screen burn.

Letterbox Mode
A way of presenting 16:9 ratio wide-screen movies on a TV screen with a 4:3 ratio. Black bars are added to the top and the bottom of the picture thus resizing the area of the TV actually used to view the moving image. As it is standard for all HDTV to be broadcast in 16:9 ratio the term wide-screen becomes essentially obsolete.

MPEG
Compression standards as agreed upon by the Motion Pictures Expert Group - the international group of industry experts who set standards for compression of audio and video. MPEG-2 has been specified for HDTV broadcasts but some suppliers, particularly those looking at IPTV as a medium for broadcast are already looking into MPEG-4.

MPEG-2
This compression standard was designed to cover a range of digital video requirements from something fairly low like VHS quality to HDTV. It is also used in DVD encoding where it is converted into a VOB file.

PAL
Phase Alternating Line is a colour encoding system used for broadcast television systems in large parts of the world including some parts of Asia and Europe excepting France and Eastern Europe, where SECAM is the standard. PAL signals run at 25 frames per second and so are incompatible with NTSC which run at 30. The PAL Standard transmits 625 lines of resolution which is almost 20% more than the U.S. NTSC Standard of 525 lines. PAL is generally accepted to result in a superior quality picture to that of NTSC.

Pillarbox
A method of displaying a traditional analogue 4:3 aspect ratio image on a 16:9 widescreen display device. In order to preserve the original aspect ratio of the video content, the picture is scaled to best fit the television screen without distortion. Thus the picture can fill the height of the screen but not the width so as in the case of the letterbox display dark bars are placed either side of the moving picture.

Pixel
Short for picture element, a pixel is a single point in a graphic image. The intensity of each pixel is variable and in color systems, each pixel typically has three or four variable dimensions as red, green and blue, or cyan, magenta, yellow and black. DTV Pixels are rectangular in shape while HDTV Pixels are virtually square and significantly smaller in size. This allows High Definition pictures to contain many more pixels dots than standard definition, resulting in a far higher resolution and superior format.

Progressive Scan
In Progressive Scanning all the horizontal lines comprising a TV picture are scanned on to the screen at once. The DTV and HDTV Standards accept both Interlaced and Progressive Scan broadcast/ display methods.

Plasma Display A Plasma TV Display uses literally hundreds of thousands of miniature embedded cells to produce a picture. Each cell is equals to a single pixel and has three sub-cells. These three sub-cells are filled with plasma gas which glows red, green or blue when electrically charged . Light from the three RGB sub-cells combines to form a single coloured pixel on the screen. Plasma Display technology is still under development with a few problems that still need to be ironed out. One of the most frequent problems is due to the fact that Plasma TVs use phosphor coated screens this places them at high risk of burn-in. This happens mostly to new sets when a static image, a logo for example is displayed on screen for any length of time. Great care should be take with new Plasma TV sets to avoid this but the problem is getting better with the advancement of the technology. Plasma displays are unable to reproduce the colour black, instead various shades of gray are used. Lastly the plasma pixel-cells actually deteriorate over time causing the picture quality to gradually diminish or fade.

Resolution
A measurement of the smallest detail that is visible or can be resolved in a video image. TV resolutions may be expressed precisely as a number of pixels in an image. While a televisions resolution is influenced by the number of pixels in the image, it is vital to note that the pixel numbers alone do not define ultimate resolution. Many other factors must be taken into account, such as, the quality of any display tubes, lenses, film scanners, etc. which are used to produce the image on the screen.

In HDTV we refer to two types of resolution that are crucially different yet interact at destination ( your HDTV). Native resolution is the maximum number of pixels that your HDTV device can display. Source resolution is the number of pixels used in the broadcast of the program and this is decided by the content provider. If your HDTV has less native resolution than the source you will lose some quality, though the end result will still be vastly superior to analogue or DTV. If your TV has a higher native resolution than the source you will not reap any benefit from the unused potential.

RGB
Stands for red, green and blue - known in the art world as the primary colours of light, and therefore television. The RGB color model is used in the display of colors on a cathode ray tube (CRT), liquid crystal or plasma display of a display device. Each pixel on the screen can be represented as values for red, green and blue. These values are converted into variable intensities which are then used to display a television picture.

SECAM
Système Electronique Couleur Avec Mémoire is a TV signal format used in France, some parts of Eastern Europe and the former Soviet Union. It is not compatible with NTSC or PAL formats.

Set-top Box Also know as a receiver or tuner. In the UK not all DTV set-top boxes can receive HDTV, for example Freeview is currently incapable of this. A HDTV set-top box must be able to receive, decode and transmit the HDTV signal to your display device. Some HD television sets come with HDTV receivers built in, or you may buy one separately from a provider such as Sky. Alternatively you can choose from any number of stand-alone devices with a variety of features dependant on price.

Spectrum The range of frequencies available for over the air transmission.

Standard Definition Television (SDTV)
SDTV is the baseline format of DTV and refers to digital transmissions with 480 line resolution in either interlaced or progressive scanned format. In practical terms, he terms SDTV and DTV can be considered synonymous. SDTV offers marked improvement over conventional analogue PAL picture resolution. It is likened to comparing VHS quality to DVD because the digital transmission eliminates interference such as ghosting and snowy images - resulting from analogue broadcast interference. Bear in mind that SDTV falls far short of HDTV in both visual and audio quality.

S-Video
Separate video is an analogue video signal which carries video data as two separate signals -brightness and color, unlike composite video which carries the entire set of signals in one signal line. It does not carry audio on the same cable. It can greatly improve the picture when connecting analogue TVs to a high quality video source such as digital broadcast satellite DVD. It does not compare to HDMI or DVI however as these are digital formats.

Viewing Angle
LCDs were designed originally as computer monitors for individual, head-on viewing. When viewed from an angle early screens lost much of their visibility. With the advent of LCD TVs manufacturers are continually striving to increase viewing angles as the LCD format has a lot to offer in terms of picture quality and portability.