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Explanation of digital television terms

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Use this page to understand the terms used in reference to digital television.

Digital television

Digital television is a replacement technology for the existing free-to-air analog services that have operated for over 50 years.

Digital television transmits a broadcast signal by encoding it as a series of 0s and 1s—the digital code used in computers. It can compress the signal to provide four or more channels in the same bandwidth used by one channel of current standard television—along with better sound and about five times more picture information (picture elements, or pixels).

Digital television therefore makes more efficient use of spectrum and allows broadcasters to provide a greater range of features such as multichannels, high definition television (HD TV) and electronic program guide (EPG).

Standard definition (SD) pictures

Standard definition broadcast quality is superior to that obtained from analog television broadcasts, traditionally viewed on 4:3 television sets, and is ghost-free and in widescreen format.

The SD picture resolution is 576 lines x 720 active pixels @ 50Hz interlaced (576i).

The Government requires broadcasters to provide a digital SD signal at all times, even when high definition programs are broadcast. This is to ensure that viewers with SD receivers will always receive a digital television service, even when the higher quality high definition television signal is transmitted.

High definition (HD) pictures

High definition broadcasts have image resolution that is superior to SD pictures and to the existing analog television broadcast. HDTV offers a quality improvement of up to three times the improvement in detail.

Australian broadcasters are currently using four different levels of HD:

  • 1920 active pixels x 1080 lines @ 50Hz interlaced
  • 1440 active pixels x 1080 lines @ 50Hz interlaced
  • 1280 active pixels x 720 lines @ 50Hz progressive
  • 720 active pixels x 576 lines @ 50Hz progressive

The benefits of HD pictures at the highest resolution are particularly noticeable on larger screen sets and when using projection equipment.

HD pictures are also ghost-free and in widescreen format. When viewed on a HD capable television screen the viewer can enjoy cinema-quality viewing with Dolby Digital sound (where available with some HD programming).

Set top box receiver

A digital television set top box receives and decodes digital terrestrial television transmissions into a form suitable for display on analog television sets, display panels or other screen display devices such as computer monitors or projectors.

Analog television sets currently in use in Australia cannot display digital transmissions on their screens without a connection to a digital television set top box receiver.

The capability of a digital television set top box will depend upon its specifications.

A digital television set top box, when connected to a 4:3 analog television set, will usually give viewers an improved signal, better picture quality and multichannelling. Some set-top boxes may also provide viewers with datacasting services and video, audio and data enhancements.

Electronic program guide (EPG)

An EPG is the electronic version of a printed program guide. Using your remote control you will be able to see on-screen ‘what's on now’ and ‘what's on next’ for all free-to-air services. You may also be able to search for a particular program by theme or category—e.g. sporting programs or movies.

Extra text and picture information (such as story line, episode description, etc.) can be called up as well. The EPG is always up-to-date and available at the click of a remote control button.

Closed captioning

Closed captioning provides deaf and hearing-impaired viewers with a text version of the dialogue, songs and sound effects included in television programs. The text is usually shown in a black box at the bottom of the picture. Current analog captioning is received on analog receivers with teletext capability. Captioning is normally 'closed' to viewers but can be accessed by those who need it.

Closed captioning does not interfere with normal viewing. Some digital television set top boxes and integrated digital televisions include closed captioning decoding capability.

Consumers intending to purchase a digital television set top box or an integrated digital television and use closed captioning should, before purchase, check on the set top box or integrated digital television’s capabilities.

Closed captioning of programming is incorporated in all English language news and current affairs programs as well as for all prime time programs (6.00pm to 10.30pm).

When available, closed captions can continue to be viewed on a standard PAL teletext-capable TV set that is tuned to analog broadcasts.

See more information about captions.

Integrated digital television (iDTV)

This is a television with in-built digital television tuner for receiving and displaying digital television transmissions.

A set with iDTV generally incorporates a high quality widescreen display and a high-level audio capability with appropriate audio/video connectors. It does not require a digital television set top box, although connection of an additional set top box could provide recording or other functionality.

Multichannelling

Because a digital television broadcast signal can carry much more data than an analog television broadcast signal it is possible for broadcasters to provide more than one channel of SD television programming at the same time. This is known as multichannelling.

The ABC and SBS currently provide one multichannel each that broadcasts a wide range of programs in addition to their main services. The free-to-air commercial broadcasters will be permitted to provide one SD multichannel each from January 2009 and to provide additional multichannels once digital switchover is complete.

Broadcasters are also offering a number of program guide and information data channels and some are providing HD programs or channels.

Widescreen

Digital television is broadcast in a native widescreen mode. Widescreen television has a different aspect ratio (ratio of width to height) than traditional analog television. The aspect ratio of a widescreen is 16:9, while Australian viewers have been accustomed to viewing a 4:3 aspect ratio since television began in this country.

Widescreen will, in many cases, literally mean you see more of the picture. Most movies are currently made in 16:9 and are converted to 4:3 to allow us to watch them on television or video, so there is a lot of information that you don't see on your television that you would see in the cinema version of the film. Live sporting events will benefit in particular from the extra detail and wider frame.

For some time now television production has been converting to widescreen. The majority of local television programming is now made in widescreen and increasing amounts of overseas programming shown in Australia is also being made available in a widescreen format.

  • Document ID: 80876 |
  • Last modified: 7 March 2008, 1:02pm