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Digital television

Digital television (DTV) uses digital modulation to broadcast video and audio signals to television sets. The digital signal eliminates common artifacts from analogue broadcasting, such as ghostly and snowy images, static noises in audio.

DTV comes in two formats standard definition television (SDTV) and high definition television (HDTV).

All early SDTV television standards were analog in nature, and SDTV digital television systems derive much of their structure from the need to be compatible with analog television. In particular, the interlaced scan is a legacy of analog television.

Attempts where made during the development of digital television to prevent a repeat of the fragmentation of the global market into different standards (i.e. PAL, SECAM, NTSC). However, the world could not agree on a single standard (why?), and hence there are two major standards in existence, the European system, DVB, and the U.S. system, ATSC. (Doesn't Japan have its own system as well?). Most countries in the world have adopted DVB, but several have followed the U.S. in adopting ATSC instead (Canada, South Korea, Argentina and Taiwan). (See http://www.dvb.org/dvb_technology/worldadoption for a map, although the map is biased towards DVB.)

Is the below talking about all DTV systems, or just ATSC, or what? HDTV uses 1280x720 pixels in progressive scan mode or 1920x1080 pixels in interlace mode. SDTV has less resolution (704x480 pixels, the approximate resolution of NTSC video) but allows the bandwidth of a DTV channel to be subdivided into up to 6 sub-channels. The TV stations can use the other 5 subchannels to carry other video, audio, or any other data. Many signals carry encryption and specify use conditions (such as "may not be recorded" or "may not be viewed on displays larger than 1 m in diagonal measure") backed up with the force of law under the WIPO Copyright Treaty (and national legislation implementing it, such as the U.S. Digital Millennium Copyright Act).

Most viewers receive digital television via a set top box which decodes the digital signals in to signals that analog televisions can understand. Access to channels is controlled by a removable smart card.

Table of contents

Digital television in the UK

The UK has two major forms of digital television, a direct-to-home satellite service provided by Sky Television and digital cable television services provided by Telewest and NTL. The initial attempt at launching a digital terrestrial broadcasting service, ITV Digital, was unsuccessful and the company went into liquidation. It was replaced in late 2002 by Freeview, which uses the same DVB-T technology, but with higher levels of error correction in an attempt to counter reception problems which dogged its predecessor. Instead of Pay TV[?] services, Freeview uses the extra capacity available through digital compression[?] to provide a wider range of free-to-air[?] channels. All services are transmitted in SDTV mode. The government (perhaps optimistically) remains hopeful that it can end analog television broadcasts by 2010.

Government website: http://www.digitaltelevision.gov.uk/

Digital television in the U.S.

The US Congress and Federal Communications Commission mandated that TV stations convert to the Digital TV standard by 2003 and that stations give up their analog TV spectrum by 2006. Apparently, the plan is behind schedule, as it is believed that the sheer number of TV sets and broadcast equipment that require upgrade, as well as the prohibitive expense to the average consumer (as of November 2001, DTV sets cost well over US$1000), slows the momentum of the implementation.

Reference: ATSC (http://www.atsc.org/press/PR_Def)

Digital television in Australia

All major capital city television stations in Australia now simulcast in both analogue (PAL G/K) and digital (DVB-T) formats. However, few people yet have digital TVs, which are still expensive. The Australian government is requiring that all stations will switch to solely digital broadcasting by the late 2000s, so the current analogue television frequencies can be freed for other uses. As of January 2003, limited high definition broadcasting is scheduled to begin "soon", and the first HDTV screens and decoders have appeared in stores (though consumer uptake is unsurprisingly minimal).

Digital television in Finland

At the moment, digital television broadcasts can be seen in the visibility areas of the radio and television stations of Anjalankoski[?], Espoo, Eurajoki[?], Jyväskylä, Kuopio[?], Lahti[?], Lapua[?], Oulu, Tampere and Turku. In addition, the television station in Vaasa broadcasts the channels of the Finnish Broadcasting Company (YLE). Also many cable providers in biggest cities provide basic and pay-tv as digital. Digital television broadcasts can be received DVB-T[?], DVB-C[?] and DVB-S[?]. There are altogether 9 channels at the moment. In addition to the basic channels of YLE, MTV3[?] and Nelonen[?] - Finland, you can watch e.g. 24h news and sports channels. All the channels broadcast now are free of charge. It is possible that some of the new channels will be pay TV[?].



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