View source for Broadcast television systems

{{Short description|Standards for terrestrial television signals}}
{{Use dmy dates|date=January 2025}}
{{For|the company|Broadcast Television Systems Inc.}}

'''Broadcast''' '''television systems''' (or '''terrestrial television systems''' outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals.

[[Analog television]] systems were standardized by the [[International Telecommunication Union]] (ITU) in 1961,<ref name="auto1">[http://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-RRC.1-1961-PDF-E.pdf Final acts of the European Broadcasting Conference in the VHF and UHF bands. Stockholm, 1961.]</ref> with each system designated by a letter ([[CCIR System A|A]]-[[CCIR System N|N]]) in combination with the color standard used ([[NTSC]], [[PAL]] or [[SECAM]]) - for example PAL-B, NTSC-M, etc.). These analog systems for TV broadcasting dominated until the 2000s.

With the introduction of [[digital terrestrial television]] (DTT), they were replaced by four main systems in use around the world: [[ATSC standards|ATSC]], [[DVB]], [[ISDB]] and [[Digital Terrestrial Multimedia Broadcast|DTMB]].

== Analog television systems ==
[[File:Analog-TV-Systems.png|thumb|500px|Analog television system by nation]]
{{Analog television encoding systems by nation}}
Every analog television system bar one began as a [[black-and-white]] system. Each country, faced with local political, technical, and economic issues, later adopted a [[color television]] standard which was grafted onto an existing [[monochrome]] system such as [[CCIR System M]], using gaps in the video spectrum (explained below) to allow color transmission information to fit in the existing channels allotted. The grafting of the color transmission standards onto existing monochrome systems permitted existing monochrome television receivers predating the changeover to color television to continue to be operated as monochrome television. Because of this compatibility requirement, color standards added a second signal to the basic monochrome signal, which carries the color information. The color information is called [[chrominance]] with the symbol C, while the black and white information is called the [[Luma (video)|luminance]] with the symbol Y. Monochrome television receivers only display the luminance, while color receivers process both signals. Though in theory any monochrome system could be adopted to a color system, in practice some of the original monochrome systems proved impractical to adapt to color and were abandoned when the switch to color broadcasting was made. All countries used one of three color standards: NTSC, PAL, or SECAM. For example, CCIR System M was often used in conjunction with NTSC standard, to provide color analog television and the two together were known as NTSC-M.

=== Pre–World War II systems ===
{{Main|Television systems before 1940}}
A number of experimental and broadcast pre-WW2 systems were tested. The first ones were mechanically based and of very low resolution, sometimes with no sound. Later TV systems were electronic, and usually mentioned by their line number: [[375-line television system|375-line]] (used in Germany, Italy, US), [[405-line television system|405-line]] (used in the UK), [[441-line television system|441-line]] (used in Germany, France, Italy, US) or [[567-line television system|567-line]] (used in the Netherlands). These systems were mostly experimental and national, with no defined international standards, and didn't resume broadcasting after the war. An exception was the UK 405-line system, that resumed broadcasts and was the first to be standardized by ITU as [[System A]], remaining in operation until 1985.

=== ITU standards ===
On an international conference in [[Stockholm]] in 1961, the [[International Telecommunication Union]] designated standards for broadcast television systems ('''ITU System Letter Designation''').<ref name="auto1"/> Each standard is designated by a letter (A-M).

On [[Very high frequency|VHF]] [[Band I|bands I]], [[Band II|II]] and [[Band III|III]] the [[405-line television system|405]], [[625 lines|625]] and [[819 line|819-line]] systems could be used:
* [[CCIR System A|A]] – 405-line system, 5&nbsp;MHz video bandwidth
* [[CCIR System B|B]] – 625-line system, 7&nbsp;MHz video bandwidth
* [[CCIR System C|C]] – Belgian 625-line system, 7&nbsp;MHz video bandwidth
* [[CCIR System D|D]] – [[International Radio and Television Organisation|I.B.T.O.]] 625-line system, 8&nbsp;MHz video bandwidth
* [[CCIR System E|E]] – French 819-line system, 14&nbsp;MHz video bandwidth
* [[CCIR System F|F]] – Belgian 819-line system, 7&nbsp;MHz video bandwidth
On [[Ultra high frequency|UHF]] bands [[Band IV|Bands IV]] and [[Band V|V]] only 625-line systems were adopted, with the difference being transmission parameters like channel bandwidth.
* [[CCIR System G|G]] – 625-line system, 5&nbsp;MHz video bandwidth
* [[CCIR System H|H]] – 625-line system, 5&nbsp;MHz video bandwidth
* [[CCIR System I|I]] – 625-line system, 5.5&nbsp;MHz video bandwidth
* [[CCIR System K|K]] – 625-line system, 6&nbsp;MHz video bandwidth
* [[CCIR System L|L]] – 625-line system, 6&nbsp;MHz video bandwidth

Following further conferences and the introduction of color television, by 1966<ref name="auto2">{{Cite web |title=C.C.I.R - Documents of the Xlth Plenary Assembly Oslo, 1966 |url=https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.277.43.en.1006.pdf}}</ref> each standard was designated by a letter (A-M) in combination with a color standard (NTSC, PAL, SECAM). This completely specifies all of the monaural analog television systems in the world (for example, PAL-B, NTSC-M, etc.).

The following table gives the principal characteristics of each standard.<ref name="auto2"/> Except for [[display resolution|lines]] and [[frame rate]]s, other units are [[Hertz|megahertz]] (MHz).
* ''Also see:'' [[television channel frequencies]]

{| class="wikitable sortable" | border="1"
|+ '''World analog television systems'''<ref name="auto2"/>
|- style="background:rgb (170, 160, 150);"
! <small>Usual [[Color television|color standard]]</small>
! <small>System</small>
! <small>Introduced</small>
! [[Scan line|<small>Lines</small>]]
! <small>[[Frame rate]] (fps)</small>
! <small>[[Broadcasting|Channel]] bandwidth</small> <small>(MHz)</small>
! <small>[[VF bandwidth|Video bandwidth]] (MHz)</small>
! <small>Vision/sound carrier separation (MHz)</small>
! <small>[[Single-sideband modulation|Vestigial sideband]] (MHz)</small>
! <small>[[Modulation|Vision modulation]] (+, -)</small>
! <small>[[Modulation|Sound modulation]] (AM, FM)</small>
! <small>[[Chrominance]] [[subcarrier]] frequency (MHz)</small>
! <small>Vision/sound power ratio</small>
! <small>Assumed display device [[Gamma correction|gamma]]<ref>{{cite web |title=C.C.I.R. Report 624-4 Characteristics of television systems, 1990 |url=https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.624-4-1990-PDF-E.pdf}}</ref><ref name="auto2" /></small>
|- style="text-align:center;"
|
| [[CCIR System A|A]]
| 1936
| 405
| 25
| 5
| 3
| −3.5
| 0.75
| +
| AM
| none
| 4:1
| 2.5 - 2.0
|- style="text-align:center;"
| [[PAL]]/[[SECAM]]
| [[CCIR System B|B]]
| 1950
| 625
| 25
| 7
| 5
| +5.5
| 0.75
| -
| FM
| 4.43
|
| 2.8
|- style="text-align:center;"
|
| [[CCIR System C|C]]
| 1953
| 625
| 25
| 7
| 5
| +5.5
| 0.75
| +
| AM
| none
|
| 2.0
|- style="text-align:center;"
| SECAM/PAL
| [[CCIR System D|D]]
| 1948
| 625
| 25
| 8
| 6
| +6.5
| 0.75
| -
| FM
| 4.43
|
| 2.8
|- style="text-align:center;"
|
| [[CCIR System E|E]]
| 1949
| 819
| 25
| 14
| 10
| ±11.15
| 2.00
| +
| AM
| none
|
| 1.7
|- style="text-align:center;"
|
| [[CCIR System F|F]]
| 1953
| 819
| 25
| 7
| 5
| +5.5
| 0.75
| +
| AM
| none
|
| 2.0
|- style="text-align:center;"
| PAL/SECAM
| [[CCIR System G|G]]
| 1961
| 625
| 25
| 8
| 5
| +5.5
| 0.75
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| PAL
| [[CCIR System H|H]]
| 1961
| 625
| 25
| 8
| 5
| +5.5
| 1.25
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| PAL
| [[CCIR System I|I]]
| 1962
| 625
| 25
| 8
| 5.5
| +5.9996
| 1.25
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| [[NTSC]]
| [[NTSC-J|J]]
| 1953
| 525
| 30
| 6
| 4.2
| +4.5
| 0.75
| -
| FM
| 3.58
|
| 2.2
|- style="text-align:center;"
| SECAM/PAL
| [[CCIR System K|K]]
| 1961
| 625
| 25
| 8
| 6
| +6.5
| 0.75
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| SECAM
| [[CCIR System K1|K1]]
| 1964
| 625
| 25
| 8
| 6
| +6.5
| 1.25
| -
| FM
| 4.43
|
| 2.8
|- style="text-align:center;"
| SECAM
| [[CCIR System L|L]]
| 1961
| 625
| 25
| 8
| 6
| -6.5
| 1.25
| +
| AM
| 4.43
| 8:1
| 2.8
|- style="text-align:center;"
| NTSC/[[PAL-M]]
| [[CCIR System M|M]]
| 1941
| 525
| 30
| 6
| 4.2
| +4.5
| 0.75
| -
| FM
| 3.58/3.56
|
| 2.2
|- style="text-align:center;"
| PAL
| [[CCIR System N|N]]
| 1951
| 625
| 25
| 6
| 4.2
| +4.5
| 0.75
| -
| FM
| 3.58
|
| 2.8
|}

==== Notes by system ====
; [[CCIR System A|A]]: Early [[United Kingdom]] and [[Ireland]] VHF system (B&W only). First electronic TV system, introduced in 1936. Vestigial sideband filtering introduced in 1949. Discontinued on 23 November 1982 in Ireland and on 2 January 1985 in the UK.<ref>{{cite web |date=2012-02-12 |title=The UK 405-Line Television Network |url=http://www.pembers.freeserve.co.uk/405-Lines/index.html |access-date=2021-12-31 |website= |archive-url=https://web.archive.org/web/20120212100552/http://www.pembers.freeserve.co.uk/405-Lines/index.html |archive-date=12 February 2012 |url-status=dead}}</ref><ref name="auto">{{cite web |date=2012-03-06 |title=World Analogue Television Standards and Waveforms |url=http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |access-date=2021-12-31 |website= |archive-url=https://web.archive.org/web/20120306185600/http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |archive-date=6 March 2012 |url-status=dead}}</ref>
; [[CCIR System B|B]]: VHF-only in most Western European countries (combined with system G and H on UHF); VHF and UHF in [[Australia]]. Originally known as the Gerber standard.<ref>{{cite web |title=625-Line Television Broadcast Standards - UK Vintage Radio Repair and Restoration Discussion Forum |url=https://www.vintage-radio.net/forum/showthread.php?t=36027 |access-date=2021-12-31 |website=www.vintage-radio.net}}</ref>
; [[CCIR System C|C]]: Early VHF system; used only in [[Belgium]], [[Italy]], the [[Netherlands]], and [[Luxembourg]], as a compromise between Systems B and L. Discontinued in 1977.<ref name="auto"/>
; [[CCIR System D|D]]: The first 625-line system. Used on VHF only in most countries (combined with system K on UHF); VHF and UHF in [[China]].
; [[CCIR System E|E]]: Early [[France|French]] VHF system (B&W only); very good (near [[High-definition television|HDTV]]) picture quality but uneconomical use of bandwidth. Sound carrier separation +11.15&nbsp;MHz on odd numbered channels, -11.15&nbsp;MHz on even numbered channels. Discontinued in 1984 (France) and 1985 (Monaco).<ref>{{cite web |date=2012-08-30 |title=World Analogue Television Standards and Waveforms |url=http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |access-date=2021-12-31 |website= |archive-url=https://web.archive.org/web/20120830232230/http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |archive-date=30 August 2012 |url-status=dead}}</ref>
; [[CCIR System F|F]]: Early VHF system used only in Belgium and Luxembourg; allowed French 819-line [[Television show|television programming]] to be broadcast on the 7&nbsp;MHz VHF channels used in those countries, at a substantial cost in horizontal resolution. Discontinued in 1968 (Belgium) and 1971 (Luxembourg).<ref name="auto"/>
; [[CCIR System G|G]]: UHF only; used in countries with [[CCIR System B|System B]] on VHF, except Australia.
; [[CCIR System H|H]]: UHF only; used only in Belgium, Luxembourg, and the Netherlands. Similar to System G with a 1.25&nbsp;MHz vestigal sideband.
; [[CCIR System I|I]]: Used in the [[United Kingdom|UK]], [[Ireland]], [[Southern Africa]], [[Macau]], [[Hong Kong]], and [[Falkland Islands]].
; [[NTSC-J|J]]: Used in [[Japan]] (see system M below). Identical to system M except that a different black level of 0 [[IRE (unit)|IRE]] is used instead of 7.5 IRE. Although the ITU specified a frame rate of 30 fields, 29.97 was adopted with the introduction of NTSC color to minimize visual artifacts. Discontinued in 2012, when Japan transitioned to [[Digital television transition|digital]].
; [[CCIR System K|K]]: UHF only; used in countries with system D on VHF, except China, and identical to it in most respects.
; [[CCIR System K1|K1]]: Used only in [[Overseas France|French overseas departments and territories]].
; [[CCIR System L|L]]: Used only in [[France]]. On VHF Band 1 only, the audio is at −6.5&nbsp;MHz. Discontinued in 2011, when France transitioned to [[Digital television transition|digital]]. It was the last system to use positive video modulation and AM sound.
; [[CCIR System M|M]]: Used in most of the [[Americas]] and [[Caribbean]] (except [[Argentina]], [[Paraguay]], [[Uruguay]], and [[French Guiana]]), [[Myanmar]], [[South Korea]], [[Republic of China|Taiwan]], [[Philippines]] (all NTSC-M), [[Brazil]] ([[PAL-M]]), [[Vietnam]], [[Cambodia]], and [[Laos]] (all SECAM-M). Although the ITU specified a frame rate of 30 fields, 29.97 was adopted with the introduction of NTSC color to minimize visual artifacts.
; [[CCIR System N|N]]: Adopted by [[Argentina]], [[Paraguay]], and [[Uruguay]] (all [[PAL#PAL-N|PAL-N]] since 1980).

=== Evolution ===
For historical reasons, some countries use a different video system on [[Ultra high frequency|UHF]] than they do on the [[Very high frequency|VHF]] bands. In a few countries, most notably the [[United Kingdom]], television broadcasting on VHF has been entirely shut down. The British [[405-line television system|405-line]] system A, unlike all the other systems, suppressed the upper sideband rather than the lower—befitting its status as the oldest operating television system to survive into the color era (although was never officially broadcast with color encoding). System A was tested with all three color standards, and production equipment was designed and ready to be built; System A might have survived, as NTSC-A, had the British government not decided to harmonize with the rest of Europe on a 625-line video system, implemented in Britain as PAL-I on UHF only.

The French [[819 line]] system E was a post-war effort to advance [[France]]'s standing in television technology. Its 819 lines were almost high definition even by today's standards. Like the British system A, it was VHF only and remained black & white until its shutdown in 1984 in France and 1985 in Monaco. It was tested with SECAM standard in the early stages, but later the decision was made to adopt color in 625-lines L system only. Thus, France adopted system L both on UHF and VHF networks and abandoned system E.

Japan had the earliest working HDTV system ([[Multiple sub-Nyquist sampling encoding|MUSE]]), with design efforts going back to 1979. The country began broadcasting wideband analog [[high-definition video]] signals in the late 1980s using an interlaced resolution of 1,125 lines, supported by the [[Sony HDVS]] line of equipment.

In many parts of the world, analog television broadcasting has been shut down completely, or in process of shutdown; see [[Digital television transition]] for a timeline of the analog shutdown.

=== Technical aspects ===

==== Frames ====
{{Main|Film frame}}
Ignoring color, all television systems work in essentially the same manner. The monochrome image seen by a camera (later, the [[Luma (video)|luminance]] component of a color image) is divided into horizontal ''scan lines'', some number of which make up a single image or ''frame''. A monochrome image is theoretically continuous, and thus unlimited in horizontal resolution, but to make television practical, a limit had to be placed on the [[Bandwidth (signal processing)|bandwidth]] of the television signal, which puts an ultimate limit on the horizontal resolution possible. When color was introduced, this limit necessarily became fixed. All analog television systems are ''[[Interlaced video|interlaced]]'': alternate rows of the frame are transmitted in sequence, followed by the remaining rows in their sequence. Each half of the frame is called a ''[[Field (video)|video field]]'', and the rate at which fields are transmitted is one of the fundamental parameters of a video system. It is related to the [[utility frequency]] at which the [[Electric power distribution|electricity distribution]] system operates, to avoid flicker resulting from the [[Beat (acoustics)|beat]] between the television screen deflection system and nearby mains generated magnetic fields. All digital, or "fixed pixel," displays have [[progressive scan]]ning and must [[Deinterlacing|deinterlace]] an interlaced source. Use of inexpensive deinterlacing hardware is a typical difference between lower- vs. higher-priced [[Flat-panel display|flat panel displays]] ([[Plasma display]], [[Liquid-crystal display|LCD]], etc.).

All [[film]]s and other filmed material shot at 24&nbsp;frames per second must be transferred to video [[frame rate]]s using a [[telecine]] in order to prevent severe motion jitter effects. Typically, for 25&nbsp;frame/s formats (European among other countries with 50&nbsp;Hz mains supply), the content is [[576i#PAL speed-up|PAL speedup]], while a technique known as "[[Three-two pull down|3:2 pulldown]]" is used for 30&nbsp;frame/s formats (North America among other countries with 60&nbsp;Hz mains supply) to match the film frame rate to the video frame rate without speeding up the play back.

==== Viewing technology ====
Analog television signal standards are designed to be displayed on a [[Cathode-ray tube|cathode ray tube]] (CRT), and so the physics of these devices necessarily controls the format of the video signal. The image on a CRT is painted by a moving beam of electrons which hits a [[phosphor]] coating on the front of the tube. This electron beam is steered by a magnetic field generated by powerful [[electromagnet]]s close to the source of the electron beam.

In order to reorient this magnetic steering mechanism, a certain amount of time is required due to the [[inductance]] of the magnets; the greater the change, the greater the time it takes for the electron beam to settle in the new spot.

For this reason, it is necessary to shut off the electron beam (corresponding to a video signal of [[zero luminance]]) during the time it takes to reorient the beam from the end of one line to the beginning of the next (''horizontal retrace'') and from the bottom of the screen to the top (''vertical retrace'' or ''[[vertical blanking interval]]''). The horizontal retrace is accounted for in the time allotted to each scan line, but the vertical retrace is accounted for as ''phantom lines'' which are never displayed but which are included in the number of lines per frame defined for each video system. Since the electron beam must be turned off in any case, the result is gaps in the television signal, which can be used to transmit other information, such as test signals or color identification signals.

The temporal gaps translate into a comb-like [[Spectral density|frequency spectrum]] for the signal, where the teeth are spaced at line frequency and concentrate most of the energy; the space between the teeth can be used to insert a color subcarrier.

==== Hidden signaling ====
Broadcasters later developed mechanisms to transmit digital information on the phantom lines, used mostly for [[teletext]] and [[closed captioning]]:
* [[PALplus]] uses a [[Widescreen signaling|hidden signaling]] scheme to indicate if it exists, and if so what operational mode it is in.
* [[NTSC]] was modified by the [[ATSC standards|Advanced Television Systems Committee]] to support an [[ghost-canceling reference|anti-ghosting signal]] that is inserted on a non-visible scan line.
* [[Teletext]] uses hidden signaling to transmit information pages.
* [[NTSC]] [[Closed captioning|Closed Captioning]] signaling uses signaling that is nearly identical to [[teletext]] signaling.
* [[Widescreen signaling]] enables a flag to indicate that a 16:9 widescreen image is being broadcast, and allows the TV set to switch to the appropriate display mode.

==== Overscan ====
{{Main|Overscan}}
Television images are unique in that they must incorporate regions of the picture with reasonable-quality content, that will never be seen by some viewers.{{Vague|date=September 2017}}

==== Interlacing ====
{{Main|Interlaced video}}
In a purely analog system, field order is merely a matter of convention. For digitally recorded material it becomes necessary to rearrange the field order when conversion takes place from one standard to another.

==== Image signal polarity ====
Another parameter of analog television systems, minor by comparison, is the choice of whether vision modulation is positive or negative. Some of the earliest electronic television systems such as the British 405-line (System A) used positive modulation. It was also used in the two Belgian systems (System C, 625 lines, and System F, 819 lines) and the two French systems (System E, 819 lines, and System L, 625 lines). In positive modulation systems, as in the earlier [[white facsimile transmission]] standard, the maximum luminance value is represented by the maximum carrier power; in negative [[modulation]], the maximum luminance value is represented by zero carrier power. All newer analog video systems use negative modulation with the exception of the French System L.

Impulse noise, especially from older automotive ignition systems, caused white spots to appear on the screens of television receivers using positive modulation but they could use simple synchronization circuits. Impulse noise in negative-modulation systems appears as dark spots that are less visible, but picture synchronization was seriously degraded when using simple synchronization. The synchronization problem was overcome with the invention of [[Phase-locked loop|phase-locked synchronization circuits]]. When these first appeared in Britain in the early 1950s one name used to describe them was "flywheel synchronisation."

Older televisions for positive-modulation systems were sometimes equipped with a peak video signal inverter that would turn the white interference spots dark. This was usually user-adjustable with a control on the rear of the television labeled "White Spot Limiter" in Britain or "Antiparasite" in France. If adjusted incorrectly it would turn bright white picture content dark. Most of the positive modulation television systems ceased operation by the mid-1980s. The French System L continued on up to the transition to digital broadcasting. Positive modulation was one of several unique technical features that originally protected the French electronics and broadcasting industry from foreign competition and rendered French TV sets incapable of receiving broadcasts from neighboring countries.

Another advantage of negative modulation is that, since the synchronizing pulses represent maximum carrier power, it is relatively easy to arrange the receiver [[automatic gain control]] to only operate during sync pulses and thus get a constant amplitude video signal to drive the rest of the TV set. This was not possible for many years with positive modulation as the peak carrier power varied depending on picture content. Modern digital processing circuits have achieved a similar effect but using the front porch of the video signal.

==== Modulation ====
Given all of these parameters, the result is a mostly-continuous [[analog signal]] which can be modulated onto a radio-frequency carrier and transmitted through an antenna. All analog television systems use [[Single-sideband modulation#Vestigial sideband (VSB)|vestigial sideband modulation]], a form of [[amplitude modulation]] in which one sideband is partially removed. This reduces the bandwidth of the transmitted signal, enabling narrower channels to be used.

==== Audio ====
In analog television, the [[Analog recording|analog audio]] portion of a broadcast is invariably modulated separately from the video. Most commonly, the audio and video are combined at the transmitter before being presented to the antenna, but separate aural and visual antennas can be used. In all cases where negative video is used, [[frequency modulation|FM]] is used for the standard [[monaural]] audio; systems with positive video use AM sound and intercarrier receiver technology cannot be incorporated. Stereo, or more generally multi-channel, audio is encoded using a number of schemes which (except in the French systems) are independent of the video system. The principal systems are [[NICAM]], which uses a digital audio encoding; double-FM (known under a variety of names, notably [[Zweikanalton]], A2 Stereo, West German Stereo, German Stereo or IGR Stereo), in which case each audio channel is separately modulated in FM and added to the broadcast signal; and BTSC (also known as [[Multichannel Television Sound|MTS]]), which multiplexes additional audio channels into the FM audio carrier. All three systems are compatible with monaural FM audio, but only [[NICAM]] may be used with the French AM audio systems.

== Digital television systems ==
The situation with worldwide digital television is much simpler by comparison. Most digital television systems are based on the [[MPEG transport stream]] standard, and use the [[H.262/MPEG-2 Part 2]] video [[codec]]. They differ significantly in the details of how the transport stream is converted into a broadcast signal, in the video format prior to encoding (or alternatively, after decoding), and in the audio format. This has not prevented the creation of an international standard that includes both major systems, even though they are incompatible in almost every respect.

The two principal digital broadcasting systems are [[ATSC standards]], developed by the [[Advanced Television Systems Committee]] and adopted as a standard in most of [[North America]], and [[DVB-T]], the '''D'''igital '''V'''ideo '''B'''roadcast – '''T'''errestrial system used in most of the rest of the world. [[DVB-T]] was designed for format compatibility with existing [[Satellite television|direct broadcast satellite]] services in Europe (which use the [[DVB-S]] standard, and also sees some use in [[Satellite television|direct-to-home]] satellite dish providers in [[North America]]), and there is also a [[DVB-C]] version for cable television. While the ATSC standard also includes support for satellite and cable television systems, operators of those systems have chosen other technologies (principally DVB-S or proprietary systems for satellite and [[Quadrature amplitude modulation|256QAM]] replacing VSB for cable). Japan uses a third system, closely related to DVB-T, called [[ISDB#ISDB-T|ISDB-T]], which is compatible with [[Brazil]]'s [[ISDB-T International|SBTVD]]. The [[China|People's Republic of China]] has developed a fourth system, named [[Digital Terrestrial Multimedia Broadcast|DMB-T/H]].

[[File:Digital broadcast standards.svg|thumb|600px|center|DTT broadcasting systems<ref>[http://www.dvb.org/about_dvb/dvb_worldwide/index.xml DVB.org] {{webarchive |url=https://web.archive.org/web/20110320104407/http://www.dvb.org/about_dvb/dvb_worldwide/index.xml |date=2011-03-20}}, Official information taken from the DVB website</ref>]]

=== ATSC ===
{{Main|ATSC standards}}
The terrestrial ATSC system (unofficially ATSC-T) uses a proprietary [[Zenith Electronics|Zenith]]-developed modulation called [[8VSB|8-VSB]]; as the name implies, it is a vestigial sideband technique. Essentially, analog VSB is to regular amplitude modulation as 8VSB is to eight-way [[quadrature amplitude modulation]]. This system was chosen specifically to provide for maximum spectral compatibility between existing analog TV and new digital stations in the United States' already-crowded television allocations system, although it is inferior to the other digital systems in dealing with [[Multipath propagation#Interference|multipath interference]]; however, it is better at dealing with [[Electromagnetic interference|impulse noise]] which is especially present on the VHF bands that other countries have discontinued from TV use, but are still used in the U.S. There is also no [[hierarchical modulation]]. After demodulation and error-correction, the 8-VSB modulation supports a digital data stream of about 19.39&nbsp;Mbit/s, enough for one high-definition video stream or several standard-definition services. See [[Digital subchannel#Technical considerations|Digital subchannel: Technical considerations]] for more information.

On November 17, 2017, the FCC voted 3-2 in favor of authorizing voluntary deployments of [[ATSC 3.0]], which was designed as the successor to the original ATSC "1.0", and issued a Report and Order to that effect. Full-power stations will be required to maintain a simulcast of their channels on an ATSC 1.0-compatible signal if they decide to deploy an ATSC 3.0 service.<ref>{{cite web |url=https://www.fcc.gov/document/fcc-authorizes-next-gen-tv-broadcast-standard |title=FCC Authorizes Next Gen TV Broadcast Standard |website=Federal Communications Commission |date=16 November 2017 |access-date=2017-11-18}}</ref>

On cable, ATSC usually uses [[Quadrature amplitude modulation#Digital QAM|256QAM]], although some use [[16VSB]]. Both of these double the [[Network throughput|throughput]] to 38.78&nbsp;Mbit/s within the same 6&nbsp;MHz [[Bandwidth (signal processing)|bandwidth]]. ATSC is also used over satellite. While these are logically called ATSC-C and ATSC-S, these terms were never officially defined.

=== DTMB ===
{{Main|DTMB}}
DTMB is the digital television broadcasting standard of the [[Mainland China]], [[Hong Kong]] and [[Macau]]. This is a fusion system, which is a compromise of different competing proposing standards from different Chinese Universities, which incorporates elements from [[Digital Terrestrial Multimedia Broadcast|DMB-T]], ADTB-T and TiMi 3.

=== DVB ===
{{Main|Digital Video Broadcasting|DVB-T|DVB-S|DVB-C}}
'''DVB-T''' uses [[Orthogonal frequency-division multiplexing|coded orthogonal frequency division multiplexing]] (COFDM), which uses as many as 8000 independent carriers, each transmitting data at a comparatively low rate. This system was designed to provide superior immunity from [[multipath interference]], and has a choice of system variants which allow data rates from 4&nbsp;MBit/s up to 24&nbsp;MBit/s. One US broadcaster, [[Sinclair Broadcast Group|Sinclair Broadcasting]], petitioned the [[Federal Communications Commission]] to permit the use of COFDM instead of 8-VSB, on the theory that this would improve prospects for digital TV reception by households without outside antennas (a majority in the US), but this request was denied. (However, one US digital station, WNYE-DT in [[New York City|New York]], was temporarily converted to COFDM modulation on an emergency basis for [[datacasting]] information to emergency services personnel in lower [[Manhattan]] in the aftermath of the [[September 11 attacks|September 11 terrorist attacks]]).

'''DVB-S''' is the original [[DVB|Digital Video Broadcasting]] forward error coding and modulation standard for [[satellite television]] and dates back to 1995. It is used via satellites serving every continent of the world, including [[North America]]. DVB-S is used in both [[Multiplexing#Digital broadcasting|MCPC]] and [[Single channel per carrier|SCPC]] modes for [[broadcast network]] [[feed (telecom)|feeds]], as well as for [[Satellite television|direct broadcast satellite]] services like [[Sky UK|Sky]] and [[Freesat]] in the British Isles, [[Sky Deutschland]] and [[HD+]] in Germany and Austria, TNT Sat/Fransat and [[Canal+ (French TV provider)|CanalSat]] in France, [[Dish Network]] in the US, and [[Bell Satellite TV]] in Canada. The [[MPEG transport stream]] delivered by DVB-S is mandated as MPEG-2.

'''DVB-C''' stands for '''Digital Video Broadcasting - Cable''' and it is the DVB European consortium standard for the broadcast transmission of [[digital television]] over [[coaxial cable|cable]]. This system transmits an [[MPEG-2]] family digital audio/video stream, using a [[Quadrature amplitude modulation|QAM]] modulation with [[Coding theory#Channel coding|channel coding]].

=== ISDB ===
ISDB is very similar to DVB, however it is broken into 13 subchannels. Twelve are used for TV, while the last serves either as a [[guard band]], or for the [[1seg]] (ISDB-H) service. Like the other DTV systems, the ISDB types differ mainly in the modulations used, due to the requirements of different frequency bands. The 12&nbsp;GHz band ISDB-S uses PSK modulation, 2.6&nbsp;GHz band digital sound broadcasting uses CDM and ISDB-T (in VHF and/or UHF band) uses COFDM with PSK/QAM. It was developed in Japan with MPEG-2, and is now used in Brazil with MPEG-4. Unlike other digital broadcast systems, ISDB includes [[digital rights management]] to restrict recording of programming.

=== Comparison of digital terrestrial television systems ===
{| class="wikitable collapsible collapsed sortable" style="text-align:center;"
|+ '''World television systems'''
|- style="background:rgb (170, 160, 150);"
! System
! Year ratified
! Digital [[Modulation]]
! Resolution<br />(Lines)
! Frame rate
! Data rate
! [[Hierarchical modulation|Hierarchical Mod.]]
! [[Television channel|Ch.]] [[Bandwidth (signal processing)|B/W]]<br />([[Hertz|MHz]])
! Video B/W
! Audio offset
! Video Coding
! Audio Coding
! [[Interactive television|Interactive TV]]
! [[Digital subchannel]]s
! Single-Frequency Network
! Predecessor format(s)
! Mobile
|-
| [[ATSC standards|ATSC]] 1.0
|
| [[8VSB]], [[A-VSB]] and [[E-VSB]] in the works
| 1080
| Up to 60p
| 19.39&nbsp;Mbit/s
| No
| 6
| 4.25<br />[[NTSC#Transmission modulation scheme|digital carrier at 1.31 MHz]]
| ?
| [[H.262/MPEG-2 Part 2|H.262]]
| [[Dolby Digital]], [[Dolby Digital#Dolby AC-3|AC3]], [[MPEG-1 Layer II]]
| [[DSM CC|DSM-CC]], [[MHEG-5]], [[Program and System Information Protocol|PSIP]]
| Yes
| [[Distributed transmission system|Partial]]
| [[NTSC]]
| Not yet, [[ATSC-M/H]] in the works
|-
| [[ATSC 3.0]]
| 2016
| [[Orthogonal frequency-division multiplexing|COFDM]]<br />([[Phase-shift keying#Quadrature phase-shift keying .28QPSK.29|QPSK]], [[Quadrature amplitude modulation|4096QAM]])
| [[2160p]]/[[4K resolution|4K]]
| Up to 120p
| 57&nbsp;Mbit/s
| Yes
| 6
| 4.5
| ?
| [[High Efficiency Video Coding|H.265/Scalable HEVC]]
| [[Dolby AC-4]], [[MPEG-H]]
| Yes
| Yes
| Yes
| [[NTSC]], [[ATSC standards|ATSC]] 1.0
| Yes
|-
|| [[DVB-T]]
| 1997
| [[Orthogonal frequency-division multiplexing|COFDM]]<br />([[Phase-shift keying#Quadrature phase-shift keying .28QPSK.29|QPSK]], [[Quadrature amplitude modulation|16QAM]]/[[Quadrature amplitude modulation|64QAM]])
| 1080 (typical, not defined)
| Up to 50p
| Up to 31.668&nbsp;Mbit/s
| Yes
| 5, 6, 7, or 8
| ?
| ?
| [[H.262/MPEG-2 Part 2|H.262]], [[Advanced Video Coding|H.264]]
| [[Dolby Digital]], [[MPEG-1 Layer II]], [[High-Efficiency Advanced Audio Coding|HE-AAC]]
| [[DSM CC|DSM-CC]], [[MHEG-5]], DVB-SI
| [[Télévision Numérique Terrestre|Yes]]
| Yes
| [[PAL]], [[SECAM]]
| Yes ([[DVB-H]])
|-
| [[DVB-T2]]
| 2008
| [[Orthogonal frequency-division multiplexing|COFDM]]<br />(QPSK, [[Quadrature amplitude modulation|16QAM]], [[Quadrature amplitude modulation|64QAM]], [[Quadrature amplitude modulation|256QAM]])
| 1080 (typical, not defined)
| Up to 50p
| Up to 50.34&nbsp;Mbit/s
| Yes
| 1.7, 5, 6, 7, 8, or 10
| ?
| ?
| [[H.262/MPEG-2 Part 2|H.262]], [[Advanced Video Coding|H.264]], [[High Efficiency Video Coding|H.265]]
| [[Dolby Digital]], [[MPEG-1 Layer II]], [[High-Efficiency Advanced Audio Coding|HE-AAC]]
| [[DSM CC|DSM-CC]], [[MHEG-5]], DVB-SI
| Yes
| Yes
| DVB-T
| [[DVB-H#DVB-NGH|DVB-NGH]]
|-
| [[DTMB]]
| 2006
| TDS-[[Orthogonal frequency-division multiplexing|OFDM]]
| 1080
| Up to 50p
| ?
| ?
| 6, 7, or 8
| ?
| ?
| [[MPEG-2]], [[Advanced Video Coding|H.264/MPEG-4 AVC]], [[Audio Video Standard|AVS]]
| [[MPEG-1 Audio Layer II]], [[Dolby Digital#Dolby AC-3|AC3]], DRA
| [[MHEG-5|Yes]]
| ?
| Yes
| [[PAL]]
| Yes
|-
| [[ISDB#ISDB-T|ISDB-T]]
| 1999
| [[Quadrature amplitude modulation|16]]/[[Quadrature amplitude modulation|64QAM]]-[[Orthogonal frequency-division multiplexing|OFDM]]<br />([[Phase-shift keying#Quadrature phase-shift keying .28QPSK.29|QPSK]]-[[Orthogonal frequency-division multiplexing|OFDM]]/[[Phase-shift keying#Quadrature phase-shift keying .28QPSK.29|DQPSK]]-[[Orthogonal frequency-division multiplexing|OFDM]])
| 1080
| Up to 60p
| 23&nbsp;Mbit/s
| Yes
| 6 (5.572 + 428&nbsp;kHz guard band)
| ?
| ?
| [[H.262/MPEG-2 Part 2|H.262]]<br />[[Advanced Video Coding|H.264]] ([[1seg]])
| [[Advanced Audio Coding|AAC]]
| No
| Yes
| Yes
| [[NTSC]]
| Yes, [[ISDB#ISDB-Tmm|ISDB-Tmm]]/[[1seg]]
|-
| [[ISDB-T International|ISDB-Tb]]<br /><small>([[ISDB-T International|SBTVD]])</small>
|
| BST-[[Orthogonal frequency-division multiplexing|OFDM]]
| 1080
| ?
| ?
| Yes
| 6
| ?
| ?
| [[Advanced Video Coding|H.264]]
| [[High-Efficiency Advanced Audio Coding|HE-AAC]]
| Yes, [[Ginga (middleware)|Ginga]]
| Yes
| Yes
| [[PAL-M]], PAL-N, NTSC
| Yes, [[1seg]]
|-
| [[MediaFLO]]
|
| [[Orthogonal frequency-division multiplexing|OFDM]]<br />([[Phase-shift keying#Quadrature phase-shift keying .28QPSK.29|QPSK]]/[[Quadrature amplitude modulation|16QAM]])
| ?
| ?
| ?
| ?
| 5.55
| ?
| ?
| ?
| ?
| Yes
| ?
| ?
| [[NTSC]] ([[Channel 55 (disambiguation)|Channel 55]])
| Yes
|-
| [[Digital multimedia broadcasting#T-DMB|T-DMB]]
|
| [[Orthogonal frequency-division multiplexing|OFDM]]-[[Phase-shift keying#Quadrature phase-shift keying .28QPSK.29|DQPSK]]
| ?
| ?
| ?
| ?
| ?
| ?
| ?
| [[H.262/MPEG-2 Part 2|H.262]]/[[Advanced Video Coding|H.264]]
| [[High-Efficiency Advanced Audio Coding|HE-AAC]]
| ?
| ?
| ?
| [[NTSC]]
| Yes
|}

== Line count ==
As interlaced systems require accurate positioning of scanning lines, it is important to make sure that the horizontal and vertical timebase are in a precise ratio. This is accomplished by passing the one through a series of electronic divider circuits to produce the other. Each division is by a [[prime number]].

Therefore, there has to be a straightforward mathematical relationship between the line and field frequencies, the latter being derived by dividing down from the former. Technology constraints of the 1930s meant that this division process could only be done using small integers, preferably no greater than 7, for good stability. The number of lines was odd because of 2:1 interlace. The 405 line system used a vertical frequency of 50&nbsp;[[Hertz|Hz]] (Standard AC mains supply frequency in Britain) and a horizontal one of 10,125&nbsp;Hz (<span title="frame rate">50</span> × <span title="lines">405</span> ÷ <span title="interlace">2</span>)
* 2 × 3 × 3 × 5 gives [[90-line television system|90 lines]] (non interlaced)
* 2 × 2 × 2 × 2 × 2 × 3 gives [[96-line television system|96 lines]] (non interlaced)
* 2 × 2 × 3 × 3 × 5 gives [[180-line television system|180 lines]] (non interlaced) (used in Germany in mid-1930s before switch to 441-line system)
* 2 × 2 × 2 × 2 × 3 × 5 gives [[240-line television system|240 lines]] (used for the experimental [[John Logie Baird|Baird]] transmissions in Britain <small>[See Note 1]</small>)
* 3 × 3 × 3 × 3 × 3 gives [[243-line television system|243 lines]]
* 7 × 7 × 7 gives [[343-line television system|343 lines]] (early North American system also used in Poland and in Soviet Union before WW2)
* 3 × 5 × 5 × 5 gives [[375-line television system|375 lines]]
* 3 × 3 × 3 × 3 × 5 gives [[405-line television system|405 lines]] [[CCIR System A|System A]] (used in Britain, Ireland and Hong Kong before 1985)
* 2 × 2 × 2 × 5 × 11 gives [[440-line television system|440 lines]] (non interlaced)
* 3 × 3 × 7 × 7 gives [[441-line television system|441 lines]] (used by [[RCA Corporation|RCA]] in North America before the 525-lines [[NTSC]] standard was adopted and widely used before WW2 in Continental Europe with different frame rates)
* 2 × 3 × 3 × 5 × 5 gives [[450-line television system|450 lines]] (non interlaced)
* 5 × 7 × 13 gives [[455-line television system|455 lines]] (used in France before WW2)
* 3 × 5 × 5 × 7 gives [[525 lines]] [[CCIR System M|System M]] ([[480i]]) (a compromise between the RCA and Philco systems. Still used today in most of the Americas and parts of Asia)
* 3 × 3 × 3 × 3 × 7 gives [[567-line television system|567 lines]] (Developed by [[Philips]] used for a while in the late 1940s in the Netherlands)
* 5 × 11 × 11 gives [[605-line television system|605 lines]] (proposed by [[Philco]] in North America before the 525 standard was adopted){{Citation needed|date=July 2024}}
* 5 × 5 × 5 × 5 gives [[625 lines]] ([[576i]]) (designed by Soviet<ref name="60TH_ANNIVERSARY_OF_625">[http://625.625-net.ru/files/587/511/h_665921be9883776271895912fb8bb262 On the beginning of broadcast in 625-lines 60 year s ago, ''625'' magazine (in Russian).] {{webarchive |url=https://web.archive.org/web/20160304131236/http://625.625-net.ru/files/587/511/h_665921be9883776271895912fb8bb262 |date=2016-03-04}}</ref><ref>{{cite web |title=Mark Iosifovich Krivosheev – an engineer's engineer |url=http://www.ebu.ch/en/technical/trev/trev_255-portrait.pdf |url-status=dead |archive-url=https://web.archive.org/web/20041230091501/http://www.ebu.ch/en/technical/trev/trev_255-portrait.pdf |archive-date=30 December 2004 |website=}}</ref><ref>{{cite web |title=In the vanguard of television broadcasting |url=http://cra.ir/FTD/Static/RRC/RRCFile10.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070221210300/http://cra.ir/FTD/Static/RRC/RRCFile10.pdf |archive-date=21 February 2007 |website=}}</ref><ref>{{cite web |last=Observer |first=Reflective |date=2021-12-23 |title=Where did 625-line TV come from? |url=https://reflectiveobserver.medium.com/from-russia-with-television-a3d02007e22a |access-date=2021-12-31 |website=Medium |language=en}}</ref><ref>{{cite web |title=625-Line Television System Origins - UK Vintage Radio Repair and Restoration Discussion Forum |url=https://www.vintage-radio.net/forum/showthread.php?t=83653 |access-date=2021-12-31 |website=www.vintage-radio.net}}</ref> engineers during the mid-late 1940s, introduced to Western Europe by German engineers.)
* 2 × 3 × 5 × 5 × 5 gives [[720-line television system|750 lines]] at 50 frames (used for [[720p|720p50]])
* 2 × 3 × 5 × 5 × 5 gives 750 lines at 60 frames (used for [[720p|720p60]])
* 3 × 3 × 7 × 13 gives [[819 line|819 lines]] ([[Analog high-definition television|737i]]) (used in France in the 1950s)
* 3 × 7 × 7 × 7 gives [[1029-line television system|1,029 lines]] (proposed but never adopted around 1948 in France)
* 3 × 3 × 5 × 5 x 5 gives [[1125-line television system|1,125 lines]] at 25 frames (used for [[1080i|1080i50]] but not [[1080p|1080p25]])
* 3 × 3 × 5 × 5 x 5 gives 1,125 lines at 30 frames (used for [[1080i|1080i60]] but not [[1080p|1080p30]])

;Notes

# The division of the 240-line system is academic as the scan ratio was determined entirely by the construction of the mechanical scanning system used with the cameras used with this transmission system.
# The division ratio though relevant to [[Cathode-ray tube|CRT]]-based systems is largely academic today because modern [[Liquid-crystal display|LCD]] and [[plasma display]]s are not constrained to having the scanning in precise ratios. The 1080p high definition system requires 1125 lines in a CRT display.
# The System I version of the 625-line standard originally used 582 active lines before later changing to 576 in line with other 625-line systems.

== Conversion from one system to another system ==
{{Main|Television standards conversion}}
{{Unreferenced section|date=May 2023}}
Converting between different numbers of lines and different frequencies of fields/frames in video pictures is not an easy task. Perhaps the most technically challenging conversion to make is from any of the 625-line, 25-frame/s systems to system M, which has 525-lines at 29.97&nbsp;frames per second. Historically this required a frame store to hold those parts of the picture not actually being output (since the scanning of any point was not time coincident). In more recent times, conversion of standards is a relatively easy task for a computer.

Aside from the line count being different, it's easy to see that generating 59.94 fields every second from a format that has only 50 fields might pose some interesting problems. Every second, an additional 10 fields must be generated seemingly from nothing. The conversion has to create new frames (from the existing input) in real time.

There are several methods used to do this, depending on the desired cost and conversion quality. The simplest possible converters simply drop every 5th line from every frame (when converting from 625 to 525) or duplicate every 4th line (when converting from 525 to 625), and then duplicate or drop some of those frames to make up the difference in frame rate. More complex systems include inter-field interpolation, adaptive interpolation, and phase correlation.

== See also ==
* [[Television antenna]] 

'''Transmission technology standards'''
* [[Amateur television]]
* [[Broadcast-safe|Broadcast safe]]
* [[Channel (broadcasting)]]
* [[Display resolution]]
* [[Lists of television channels]] for lists by country and language.
* [[Television channel frequencies]]
* [[Pan-American television frequencies]]
* [[European cable television frequencies]]
* [[Australian and New Zealand television frequencies]]

'''Defunct analog systems'''
* [[405-line television system|405 lines]]
* [[441-line television system|441 lines]]
* [[819 line]]s
* [[Multiple sub-Nyquist sampling encoding|MUSE]] an [[analog high-definition television system]].

'''Analog television systems'''
* [[Intercarrier method]]
* [[NTSC]] (525/60)
* [[PAL]] (color encoding usually used with 625/50 systems)
* [[PAL-M]]
* [[PAL#PAL-N|PAL-N]]
* [[PALplus]]
* [[SECAM]]
* [[Transposer]]s
* [[Television transmitter|TV transmitters]]

'''Analog television system audio'''
* [[Multichannel Television Sound]]
* [[NICAM]] (digital, analog pre-emphasis curve)
* [[Zweikanalton]]
* The defunct MUSE system had a very unusual digital audio subsystem completely unrelated to [[NICAM]].

'''Digital television systems'''
* [[High-definition television|HDTV]] systems all use [[Moving Picture Experts Group|MPEG]] transport technology
* [[ATSC standards]]
* [[DVB-T]] and [[DVB-T2]]
* [[ISDB]] and [[ISDB-T International]] (SBTVD)
* [[Digital Terrestrial Multimedia Broadcast|DTMB]] used in People's Republic of China, Hong Kong and Macau.

'''History'''
* [[History of television]]
* [[Prewar television stations|Oldest television station]]
* [[Television systems before 1940]]

== References ==
{{reflist}}

== Further reading ==
* Characteristics of television systems. [[International Telecommunication Union]], ITU-R Recommendation BT.470-2. [https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.624-4-1990-PDF-E.pdf]

== External links ==
* [https://web.archive.org/web/20110807095604/http://www.farway.com.ar/ FARWAY IRFC, TV and Radio Transmission, Radio Data System Encoders, Broadcasting Technologies]
* [https://web.archive.org/web/20120830232230/http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html World Analog Television Standards and Waveforms] by Alan Pemberton
* [http://stjarnhimlen.se/tv/tv.html Analog TV Broadcast Systems] by Paul Schlyter
* [http://www.earlytelevision.org/european_stations_1932.html European Television Stations in 1932] a scan from a 1932 French magazine

{{TV resolution}}
{{Video formats}}
{{SMPTE standards}}
{{Analog TV transmitter topics}}
{{Telecommunications}}

[[Category:Broadcasting standards]]
[[Category:Television technology]]
[[Category:Television terminology]]
[[Category:Television transmission standards]]