ATSC in the context of "ISDB"

A television channel, or TV channel, is a terrestrial frequency or allocated number over which a television station or television network is distributed. For example, in North America, channel 2 refers to the terrestrial or cable band of 54 to 60 MHz, with carrier frequencies of 55.25 MHz for NTSC analog video (VSB) and 59.75 MHz for analog audio (FM), or 55.31 MHz for digital ATSC (8VSB). Channels may be shared by many different television stations or cable-distributed channels depending on the location and service provider.

Depending on the multinational bandplan for a given region, analog television channels are typically 6, 7, or 8 MHz in bandwidth, and therefore television channel frequencies vary as well. Channel numbering is also different. Digital terrestrial television channels are the same as their analog predecessors for legacy reasons, however through multiplexing, each physical radio frequency (RF) channel can carry several digital subchannels. On satellites, each transponder normally carries one channel, however multiple small, independent channels can be on one transponder, with some loss of bandwidth due to the need for guard bands between unrelated transmissions. ISDB, used in Japan and Brazil, has a similar segmented mode.

Digital terrestrial television (DTT, DTV, or DTTV) is a broadcast technology that transmits television signals digitally over the air, replacing analog transmission methods. It has become the primary form of free-to-air broadcasting in many countries, offering improved picture quality and the capacity to carry multiple channels within a single frequency. Reception typically requires a television antenna and a compatible receiver, such as a HD/UHD TV or set-top box.

The conversion from analog to digital broadcasting, known as the digital transition or analog switch-off (ASO), began with experimental transmissions in the 1990s. By the mid-2000s, many governments had established timelines for phasing out analog signals, with deadlines for the changeover, often including subsidies for equipment upgrades and limited exemptions for remote areas. Regional technical standards differ widely. North America and South Korea developed ATSC 1 and ATSC 3.0, while Europe and most of Africa and Oceania primarily use DVB-T and DVB-T2. Japan and much of Central and South America adopted ISDB-T and ISDB-Tb, and China operates the DTMB standard. Some of these standards also support mobile reception and interactive features. By late 2024, the International Telecommunication Union and DVB/EBU reported that more than 160 countries had completed their DTV transition, while some states were still in various transition phases.