Digital television

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Digital television (DTV) uses digital modulation to broadcast video and audio signals to the TV sets. 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 TV (SDTV) and High Definition TV (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.html 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).

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