Why switch at all
The digital switchover is the name for the whole process of retiring analog television. Analog television ran for more than half a century, and by the 1990s it was in nearly every home in the industrialized world. Replacing it was a major public project. A government could not simply change the signal, because viewers owned many millions of sets that only understood the old one. The switch from analog to digital broadcasting therefore needed new standards, years of overlapping transmission, and public information campaigns.
The motivations were mostly practical. Digital transmission uses the radio spectrum more efficiently, because compression lets several programs, or one high-definition program, share a channel that once held one analog picture. The freed airwaves could be reassigned to other uses, including mobile services. Digital signals also resist interference, support wide-screen formats and carry extra data such as program guides and subtitles. Supporters also pointed to the chance to improve picture and sound quality. These were arguments made by regulators and broadcasters, and the actual benefits to viewers depended on the country and the services provided.
Standards
Different regions developed different digital systems during the 1990s.
- DVB (Digital Video Broadcasting): A European-led family of standards covering terrestrial (DVB-T), satellite (DVB-S) and cable (DVB-C) delivery. It was widely adopted in Europe, Australia, parts of Asia and Africa, and elsewhere.
- ATSC: The Advanced Television Systems Committee standard in North America, formally adopted in the United States in 1995 and built on work by an industry group formed in the early 1990s. It was also adopted by South Korea and some other countries.
- ISDB: Developed in Japan, with a variant adapted in Brazil and other Latin American countries.
- DTMB: A system developed in China.
Which system a country chose depended on engineering preferences, existing industry ties and trade interests. Because of the differences, television equipment is not always interchangeable between regions, though many modern sets support more than one standard.
All of these systems use digital compression, typically MPEG-2 in the first generation and more efficient methods such as H.264 and later HEVC in newer services. Newer versions of the standards, such as DVB-T2, increased capacity.
The pace of transition
There was no single global date. Countries moved on their own schedules, usually after pilot services had been running for several years.
Some small countries and regions moved early. Luxembourg, the Netherlands and Finland were among the European countries that completed their switch around the mid-to-late 2000s. In Britain, digital terrestrial television started in 1998, and the analog switch-off was carried out region by region, starting in 2007 and finishing in 2012. In the United States, Congress set a deadline for full-power stations, and the switch occurred in June 2009 after a delay from an earlier date in February. Japan completed its switchover in 2011, except for three northeastern prefectures affected by the March 2011 earthquake and tsunami, which switched in 2012. Many other countries followed over the next several years, and some have had longer timelines because of cost and coverage challenges.
Helping viewers cross over
The main practical problem was that analog sets could not decode digital signals. There were several solutions.
- Set-top boxes: Converter boxes took the digital signal and output it to the old set. In the United States, the government ran a coupon program to help households pay for them. Several other countries had similar help schemes, often aimed at older or lower-income viewers.
- Integrated sets: Newer televisions had digital tuners built in, and in some countries they were required for sale well before the switch.
- Cable and satellite: Households that received television through cable or satellite (the latter via communications satellites) were often less affected, since the provider could convert signals.
Governments and broadcasters ran public information campaigns, on-air scrolls and help lines. Some countries tested the process in a single town or region first, which helped find problems before a national switch-off. In the United Kingdom, for example, Whitehaven in Cumbria was an early test location, according to most accounts.
Not everything went smoothly. Some viewers lost reception because digital signals do not degrade gradually as analog ones did: a weak digital signal tends to freeze or disappear. Viewers sometimes needed new or adjusted antennas, and certain buildings and rural areas had gaps in coverage. Outcomes varied by place.
What happened to the airwaves
A major motive for the transition in many countries was spectrum reuse. After analog stations went off the air, regulators reassigned part of the freed band, often called the digital dividend, to mobile broadband on cellular networks and other services. In the United States, the 700 MHz band was auctioned in 2008 for this purpose. The details differ by country, and the amount of spectrum recovered depended on how many digital channels broadcasters retained.
An ongoing change
Digital switchover was not the end. Broadcasters continue to adopt newer standards, for example ATSC 3.0 in some North American markets and DVB-T2 in many other countries, and these can bring higher resolution and internet connectivity. At the same time, many viewers receive programs through broadband streaming, often on smartphones, rather than over the air. The shift from analog to digital terrestrial broadcasting was a complete change of technology, but it did not change the basic arrangement of local transmitters and household aerials, which are now being tested by competition from the internet.