Digital television (DTV) is the sending and receiving of moving images and sound by discrete (digital) signals, in contrast to the analog signals used by analog TV.

The first country to make a wholesale switch to digital over-the-air (terrestrial) broadcasting was Luxembourg, in 2006. Since then, the Netherlands, Finland, Andorra, Sweden, Switzerland, Germany and Portugal have followed suit.

In the United States, where most full-power television stations are already broadcasting both an analog and a digital signal, the FCC has set June 12, 2009 as the date on which all analog transmissions will cease and over-the-air broadcasts will be solely digital. By special dispensation, some analog TV signals ceased, as previously scheduled, on February 17, 2009. This has to do with station resistance to a sudden change in schedule, that will cost broadcasters money and cause logistical nightmares.

In Japan, the switch to digital is scheduled to happen July 24, 2011. In Canada, it is scheduled to happen August 31, 2011. China is scheduled to switch in 2015. In the United Kingdom, the digital switchover has different times for each part of the country; however, the whole of the UK will be digital by 2012. Brazil switched to digital on December 2, 2007 in major cities and it is estimated it will take seven years for complete signal expansion over all of the Brazilian territory.

In Malaysia, the Malaysian Communications & Multimedia Commission (MCMC) will call for tender bids in the third quarter of 2009 for the UHF 470–742 megahertz spectrum which will pave the way for the country to move into the digital television era. The awarding of the spectrum will see the winner having to build a single digital terrestrial transmission/TV broadcast (DTTB) infrastructure for all broadcasters to ride on to transmit their TV programs. The winner will be announced at the end of 2009 or early 2010 and has to commence digital roll-out soon after the award where the analog switch-off is planned for 2015.

While the majority of the viewers of over-the-air broadcasting in the USA watch full-power stations (which number about 1800), there are three other categories of TV stations in the USA: low-power stations, Class A stations, and TV translator stations. There is presently no deadline for these stations, about 7100 in number, to convert to digital broadcasting.

Technical information

Formats and bandwidth

Digital television supports many different picture formats defined by the combination of size, aspect ratio (height to width ratio) and interlacing. With terrestrial broadcasting in the USA, the range of formats can be coarsely divided into two categories: HDTV and SDTV. It should be noted that these terms by themselves are not very precise, and many subtle intermediate cases exist.

High-definition television (HDTV), one of several different formats that can be transmitted over DTV, uses one of two formats: 1280 × 720 pixels in progressive scan mode (abbreviated 720p) or 1920 × 1080 pixels in interlace mode (1080i). Each of these utilizes a 16:9 aspect ratio. (Some televisions are capable of receiving an HD resolution of 1920 × 1080 at a 60 Hz progressive scan frame rate — known as 1080p60, but this standard is not currently used for transmission.) HDTV cannot be transmitted over current analog channels.