View source for Digital television

{{Short description|Television transmission using digital encoding}}
{{More citations needed|date=May 2010}}
{{Use American English|date=November 2023}}

[[File:Digital terrestrial television standards.svg|thumb|400px|A map depicting [[digital terrestrial television]] standards]]
{{Table Digital video broadcast standards}}

'''Digital television''' ('''DTV''') is the transmission of [[television]] signals using [[Digital signal|digital]] encoding, in contrast to the earlier [[analog television]] technology which used [[analog signal]]s. In the 2000s<ref>{{Cite web |date=2008-12-22 |title=The Origins and Future Prospects of Digital Television |url=https://www.benton.org/initiatives/obligations/charting_the_digital_broadcasting_future/sec1 |access-date=2025-07-06 |website=Benton Foundation |language=en}}</ref> it was represented as the first significant evolution in television technology since [[color television]] in the 1950s.<ref>{{cite book |last=Kruger |first=Lennard G. |year=2002 |title=Digital Television: An Overview |location=New York |publisher=Nova Publishers |isbn=1-59033-502-3 |url=https://books.google.com/books?id=BIAfWq2V3wgC}}</ref> Modern digital television is transmitted in [[high-definition television]] (HDTV) with greater resolution than analog TV. It typically uses a [[widescreen]] aspect ratio (commonly [[16:9]]) in contrast to the narrower format ([[4:3]]) of analog TV. It makes more economical use of scarce [[radio spectrum]] space; it can transmit up to seven channels in the same [[Bandwidth (signal processing)|bandwidth]] as a single analog channel,<ref>{{cite web |url=http://www.disabled-world.com/artman/publish/digital-hdtv.shtml |title=HDTV Set Top Boxes and Digital TV Broadcast Information |access-date=28 June 2014 |archive-url=http://arquivo.pt/wayback/20160522191336/http://www.disabled%2Dworld.com/artman/publish/digital%2Dhdtv.shtml |archive-date=22 May 2016 |url-status=dead}}</ref> and provides many new features that analog television cannot. A [[digital television transition|transition from analog to digital broadcasting]] began around 2000. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:
* [[Digital Video Broadcasting]] (DVB) uses coded [[orthogonal frequency-division multiplexing]] (OFDM) modulation and supports hierarchical transmission. This standard has been adopted in Europe, Africa, Asia and Australia, for a total of approximately 60 countries.
* [[ATSC standards|Advanced Television System Committee]] (ATSC) standard uses eight-level vestigial sideband ([[8VSB]]) for terrestrial broadcasting. This standard has been adopted by 9 countries: the United States, Canada, Mexico, South Korea, Bahamas, Jamaica, the Dominican Republic, Haiti and Suriname.{{citation needed|date=February 2021}}
* [[Integrated Services Digital Broadcasting]] (ISDB) is a system designed to provide good reception to fixed receivers and also portable or mobile receivers utilizing OFDM and two-dimensional interleaving. It supports hierarchical transmission of up to three layers and uses [[MPEG-2 video]] and [[Advanced Audio Coding]]. This standard has been adopted in Japan and the Philippines. [[ISDB-T International]] is an adaptation of this standard using [[H.264/MPEG-4 AVC]], which has been adopted in most of [[South America]] as well as [[Botswana]] and [[Angola]]. [[1seg]] (1-segment) is a special form of [[ISDB]]. Each channel is further divided into 13 segments. Twelve are allocated for [[HDTV]] and the other for narrow-band receivers such as mobile televisions and [[cell phone]]s.
* [[Digital Terrestrial Multimedia Broadcast]] (DTMB) adopts time-domain synchronous (TDS) OFDM technology with a pseudo-random signal frame to serve as the guard interval (GI) of the OFDM block and the training symbol. The DTMB standard has been adopted in China, including Hong Kong and Macau.<ref>Ong, C. Y., Song, J., Pan, C., & Li, Y.(2010, May). Technology and Standards of Digital Television Terrestrial Multimedia Broadcasting [Topics in Wireless Communications], IEEE Communications Magazine, 48(5),119–127</ref>
* [[Digital Multimedia Broadcasting]] (DMB) is a digital radio transmission technology developed and adopted in South Korea<ref>{{cite web|url=http://www.zdnet.co.kr/ArticleView.asp?artice_id=00000039146251 |title=Korea's Terrestrial DMB: Germany to begin broadcast this May |publisher=ZDNet Korea |date= 2006-04-06|access-date=2010-06-17}}</ref><ref>{{cite web |url=http://www.textually.org/picturephoning/archives/cat_dmb.htm |title=picturephoning.com: DMB |publisher=Textually.org |access-date=2010-06-17 |url-status=dead |archive-url=https://web.archive.org/web/20100809051720/http://www.textually.org/picturephoning/archives/cat_dmb.htm |archive-date=2010-08-09 }}</ref><ref>{{cite web |url=http://www.reportworld.co.kr/cbqna/cb_answer_view.html?no=40590 |title=South Korea : Social Media 답변 내용 : 악어새 – 리포트월드 |publisher=Reportworld.co.kr |access-date=2010-06-17 |url-status=dead |archive-url=https://web.archive.org/web/20090817143122/http://www.reportworld.co.kr/cbqna/cb_answer_view.html?no=40590 |archive-date=2009-08-17 }}</ref> as part of the national [[information technology]] project for sending multimedia such as TV, radio and [[datacasting]] to [[mobile device]]s such as mobile phones, laptops and GPS navigation systems.

== History ==
=== Background ===
Digital television's roots in the 1990s are tied to the availability of inexpensive, high-performance [[computer]]s that can compress video.<ref name="benton">{{cite web |url= http://www.benton.org/initiatives/obligations/charting_the_digital_broadcasting_future/sec1 |title= The Origins and Future Prospects of Digital Television |publisher= [[Benton Foundation]] |date= 2008-12-23 }}</ref> Digital television was previously impractical due to high [[Bandwidth (computing)|bandwidth]] requirements of [[uncompressed video]],<ref name="Lea">{{cite book |last1=Lea |first1=William |title=Video on demand: Research Paper 94/68 |date=1994 |publisher=[[House of Commons Library]] |url=https://researchbriefings.parliament.uk/ResearchBriefing/Summary/RP94-68 |access-date=20 September 2019}}</ref><ref name="Barbero">{{cite journal |last1=Barbero |first1=M. |last2=Hofmann |first2=H. |last3=Wells |first3=N. D. |title=DCT source coding and current implementations for HDTV |journal=EBU Technical Review |date=14 November 1991 |issue=251 |pages=22–33 |publisher=[[European Broadcasting Union]] |url=https://tech.ebu.ch/publications/trev_251-barbero |access-date=4 November 2019}}</ref> requiring around {{val|200|ul=Mbit/s}} for a [[standard-definition television]] (SDTV) signal,<ref name="Lea"/> and over {{val|1|ul=Gbit/s}} for [[high-definition television]] (HDTV).<ref name="Barbero"/>

=== Development ===
In the mid-1980s, [[Toshiba]] commercially released one of the first [[television set|television sets]] with digital capabilities, using [[integrated circuit]] chips such as a [[microprocessor]] to convert analog television broadcast signals to [[digital video]] signals, enabling features such as freezing pictures and [[Picture-in-picture|showing two channels at once]]. Following in 1986, [[Sony]] and [[NEC Home Electronics]] announced their own similar TV sets with digital video capabilities. However, these television sets still relied on analog TV broadcast signals, with true digital TV broadcasts not yet being available at the time.<ref>{{cite magazine |last1=Meigs |first1=James B. |title=Home Video: Get set for digital |magazine=[[Popular Mechanics]] |date=June 1986 |volume=163 |issue=6 |page=52 |url=https://books.google.com/books?id=H-MDAAAAMBAJ |publisher=[[Hearst Magazines]] |issn=0032-4558}}</ref><ref>{{cite magazine |last1=Bateman |first1=Selby |title=New Technologies: The Converging Digital Universe |magazine=[[Compute!]] |date=April 1986 |issue=71 |pages=21-29 (26-8) |url=https://archive.org/details/1986-04-compute-magazine/page/n27}}</ref>

A digital TV broadcast service was proposed in 1986 by [[Nippon Telegraph and Telephone]] (NTT) and the [[Ministry of Posts and Telecommunications (Japan)|Ministry of Posts and Telecommunication]] (MPT) in Japan, where there were plans to develop an "Integrated Network System" service. However, practical digital TV service implementation was not available until the adoption of [[Motion-compensated DCT|motion-compensated DCT video compression formats]] such as [[MPEG]] made it possible in the early 1990s.<ref name="Lea"/>

In the mid-1980s, as Japanese consumer electronics firms forged ahead with the development of [[HDTV]] technology, and the [[Multiple sub-Nyquist sampling encoding|MUSE]] analog format was proposed by Japan's public broadcaster [[NHK]] as a worldwide standard. Until June 1990, the Japanese MUSE standard—based on an analog system—was the front-runner, set to eclipse US electronics company solutions, among the more than 23 different technical concepts under consideration.

Simultaneously, between 1988 and 1991, European organizations: CMMT, ETSI, etc. were working on [[Discrete cosine transform|DCT]]-based digital [[video coding standards]] for both SDTV and HDTV. The EU 256 project by the CMTT and [[ETSI]], along with research by Italian broadcaster [[RAI]], developed a DCT [[video codec]] that broadcast SDTV at {{val|34|u=Mbit/s}} and near-studio-quality HDTV at about {{nowrap|70{{ndash}}140 Mbit/s}}. RAI demonstrated this with a [[1990 FIFA World Cup]] broadcast in March 1990.<ref name="Barbero"/><ref>{{cite journal |last1=Barbero |first1=M. |last2=Stroppiana |first2=M. |title=Data compression for HDTV transmission and distribution |journal=IEE Colloquium on Applications of Video Compression in Broadcasting |date=October 1992 |pages=10/1–10/5 |url=https://ieeexplore.ieee.org/document/193745}}</ref> 

Simultaneously, in March 1990, American company [[General Instrument]] demonstrated the feasibility of a digital television signal; persuading the FCC to delay its decision on an advanced television (ATV) standard until a digitally based standard could be developed; resulting in several actions. First, the FCC declared that the new TV standard must be more than an enhanced [[analog signal]], capable of providing a genuine HDTV signal with at least twice the resolution of existing television images. Second, to ensure that viewers who did not wish to buy a new digital television set could continue to receive conventional television broadcasts, it dictated that the new ATV standard must be capable of being [[simulcast]] with [[NTSC]] on different channels. The new ATV standard also allowed the new DTV signal to be based on entirely new design principles incorporating many improvements over existing analog television.<ref name="benton" />

A universal standard for scanning formats, aspect ratios, or lines of resolution was not produced by the FCC's final standard. This outcome resulted from a dispute between the consumer [[electronics industry]] (joined by some broadcasters) and the computer industry (joined by the film industry and some public interest groups) over which of the two scanning processes—[[interlaced]] or [[Progressive scan|progressive]]—is superior. Interlaced scanning, which is used by the electronics industry in televisions worldwide, scans even-numbered lines first, then odd-numbered ones. Progressive scanning, which is the format used in computers, scans lines in sequences, from top to bottom. The computer industry argued that progressive scanning is superior because it does not [[Flicker (screen)|flicker]] in the manner of interlaced scanning. It also argued that progressive scanning enables easier connections with the Internet and is more cheaply converted to interlaced formats than vice versa. The film industry also supported progressive scanning because it offers a more efficient means of converting filmed programming into digital formats. The consumer electronics industry and broadcasters argued that interlaced scanning was the only technology that could transmit the highest quality pictures then (and currently) feasible, i.e., 1,080 lines per picture and 1,920 pixels per line. Broadcasters also favored interlaced scanning because their vast archive of interlaced programming is not readily compatible with a progressive format.<ref name="benton" />

=== Inaugural launches ===
[[DirecTV]] in the US launched the first commercial digital [[satellite television|satellite]] platform in May 1994, using the [[Digital Satellite System]] (DSS) standard.<ref>{{cite web|url=http://www.fundinguniverse.com/company-histories/u-s-satellite-broadcasting-company-inc-history/|title=History of U.S. Satellite Broadcasting Company, Inc. – FundingUniverse|website=www.fundinguniverse.com|access-date=9 August 2018}}</ref><ref>{{cite web|url=https://eu.indystar.com/story/money/2015/09/04/business-insider-digital-satellite-tv-indy-roots/71611606/|title=Business Insider: Digital satellite TV has Indy roots|access-date=9 August 2018}}</ref> [[Digital cable]] broadcasts were tested and launched in the US in 1996 by [[Tele-Communications Inc.|TCI]] and [[Time Warner]].<ref>{{cite web|url=https://money.cnn.com/1997/12/17/technology/nextlevel/|title=NextLevel signs cable deal - Dec. 17, 1997|website=money.cnn.com|access-date=9 August 2018}}</ref><ref>{{cite web|url=https://money.cnn.com/1996/08/15/companies/tci_pkg/|title=TCI faces big challenges - Aug. 15, 1996|website=money.cnn.com|access-date=9 August 2018}}</ref> The first [[digital terrestrial]] platform was launched in November 1998 as [[ONdigital]] in the UK, using the [[DVB-T]] standard.<ref>{{cite web|url=http://www.onhistory.co.uk/timeline/1998/11/10/canal-technologies-and-worlds-first-digital-terres|title=CANAL+ TECHNOLOGIES and the world's first digital terrestrial television service in the United Kingdom|access-date=9 August 2018}}</ref>

== Technical information ==

=== Formats and bandwidth ===
[[File:Digital & Analog TV screen quality comparison-1.jpg|thumbnail|right|Comparison of image quality between [[ISDB-T]] (1080i broadcast, top) and [[NTSC]] (480i transmission, bottom)]]
Digital television supports many different picture formats defined by the [[broadcast television systems]] which are a combination of size and [[aspect ratio (image)|aspect ratio]] (width to height ratio).

With [[digital terrestrial television]] (DTT) broadcasting, the range of formats can be broadly divided into two categories: [[high-definition television]] (HDTV) for the transmission of [[high-definition video]] and [[standard-definition television]] (SDTV). These terms by themselves are not very precise and many subtle intermediate cases exist.

One of several different HDTV formats that can be transmitted over DTV is: {{resx|1280|720}} [[pixel]]s in [[progressive scan]] mode (abbreviated ''[[720p]]'') or {{resx|1920|1080}} pixels in interlaced video mode (''[[1080i]]''). Each of these uses a [[16:9]] aspect ratio. Uncompressed HDTV cannot be transmitted over analog [[television channel]]s because of [[channel capacity]] issues.

SDTV, by comparison, may use one of several different formats taking the form of various aspect ratios depending on the technology used in the country of broadcast. [[NTSC]] can deliver a {{resx|640|480}} resolution in 4:3 and {{resx|854|480}} in [[16:9]], while [[PAL]] can give {{resx|768|576}} in [[4:3]] and {{resx|1024|576}} in [[16:9]]. However, broadcasters may choose to reduce these resolutions to reduce [[bit rate]] (e.g., many DVB-T channels in the UK use a horizontal resolution of 544 or 704 pixels per line).<ref>[http://dtt.me.uk Latest snapshots - Freeview/DTT bitrates] {{Webarchive|url=https://web.archive.org/web/20071122175239/http://dtt.me.uk/ |date=2007-11-22 }} (Mendip transmitter, UK)</ref>

Each [[commercial broadcasting]] [[terrestrial television]] DTV channel in North America is allocated enough bandwidth to broadcast up to 19 [[megabit]]s per second using 8VSB modulation.<ref>{{Cite web |title=Why do ATSC channels need 6MHz of bandwidth when they're digital? |url=https://dsp.stackexchange.com/questions/81951/why-do-atsc-channels-need-6mhz-of-bandwidth-when-theyre-digital |access-date=2025-07-06 |website=Signal Processing Stack Exchange |language=en}}</ref> However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead, the broadcast can use [[Program and System Information Protocol]] and subdivide across several video [[subchannel]]s (a.k.a. feeds) of varying quality and compression rates, including non-video [[datacasting]] services.

A broadcaster may opt to use a standard-definition (SDTV) digital signal instead of an [[HDTV]] signal, because current convention allows the bandwidth of a DTV channel (or "[[multiplex (TV)|multiplex]]") to be subdivided into multiple [[digital subchannel]]s, (similar to what most FM [[radio station]]s offer with [[HD Radio]]), providing multiple feeds of entirely different [[television program]]ming on the same channel. This ability to provide either a single HDTV feed or multiple lower-resolution feeds is often referred to as distributing one's bit budget or multicasting. This can sometimes be arranged automatically, using a [[statistical multiplexer]]. With some implementations, image resolution may be less directly limited by bandwidth; for example in [[DVB-T]], broadcasters can choose from several different modulation schemes, giving them the option to reduce the transmission [[bit rate]] and possibly improve reception for more distant or mobile viewers.

=== Reception ===
There are several different ways to receive digital television. One of the oldest means of receiving DTV (and TV in general) is from terrestrial transmitters using an [[Television antenna|antenna]] (known as an ''aerial'' in some countries). This delivery method is known as [[digital terrestrial television]] (DTT). With DTT, viewers are limited to channels that have a terrestrial transmitter within range of their antenna.

Other delivery methods include [[digital cable]] and [[digital satellite]]. In some countries where transmissions of TV signals are normally achieved by [[microwaves]], digital [[multichannel multipoint distribution service]] is used. Other standards, such as [[digital multimedia broadcasting]] (DMB) and [[digital video broadcasting - handheld]] (DVB-H), have been devised to allow handheld devices such as [[mobile phones]] to receive TV signals. Another way is [[Internet Protocol television]] (IPTV), which is the delivery of TV over a computer network. Finally, an alternative way is to receive digital TV signals via the open Internet ([[Internet television]]), whether from a central streaming service or a P2P (peer-to-peer) system.

Some television signals are protected by [[Television encryption|encryption]] and backed up with the force of law under the [[WIPO Copyright Treaty]] and national legislation implementing it, such as the US [[Digital Millennium Copyright Act]].<ref>{{Cite web |title=17 U.S. Code § 1201 - Circumvention of copyright protection systems |url=https://www.law.cornell.edu/uscode/text/17/1201 |access-date=2025-07-06 |website=LII / Legal Information Institute |language=en}}</ref> Access to encrypted channels can be controlled by a removable card, for example via the [[Common Interface]] or [[CableCard]].

=== Protection parameters ===
Digital television signals should not interfere with each other and many times coexist with analog television until it is phased out. The following table gives allowable signal-to-noise and signal-to-interference ratios for various interference scenarios. This table is a crucial regulatory tool for controlling the placement and power levels of digital television stations. Digital TV is more tolerant of interference than analog TV.<ref>{{Cite web|title=Frequently Asked Questions -- What Is Digital TV?|url=https://abcnews.go.com/Technology/story?id=97270&page=1|access-date=2020-09-30|website=ABC News|language=en}}</ref>

{{unreferenced section|date=May 2023}}
{| class="wikitable"
|-
! System Parameters<br /><small>(protection ratios)</small>
! Canada
! US
! EBU<br /><small>ITU-mode M3</small>
! Japan & Brazil{{efn-ua|ISDB-T (6&nbsp;MHz, 64QAM, R{{=}}2/3), Analog TV (M/NTSC).}}
|-
! C/N for AWGN Channel
| +19.5&nbsp;dB<br />(16.5&nbsp;dB{{efn-ua|name=protection_parameters_table_note_a|The Canadian parameter, C/(N+I) of noise plus co-channel DTV interface should be 16.5&nbsp;dB.}})
| +15.19&nbsp;dB
| +19.3&nbsp;dB
| +19.2&nbsp;dB
|-
! Co-Channel DTV into Analog TV
| +33.8&nbsp;dB
| +34.44&nbsp;dB
| +34 ≈37&nbsp;dB
| +38&nbsp;dB
|-
! Co-Channel Analog TV into DTV
| +7.2&nbsp;dB
| +1.81&nbsp;dB
| +4&nbsp;dB
| +4&nbsp;dB
|-
! Co-Channel DTV into DTV
| +19.5&nbsp;dB<br />(16.5&nbsp;dB{{efn-ua|name=protection_parameters_table_note_a}})
| +15.27&nbsp;dB
| +19&nbsp;dB
| +19&nbsp;dB
|-
! Lower Adjacent Channel DTV into Analog TV
| −16&nbsp;dB
| −17.43&nbsp;dB
| −5 ~ −11&nbsp;dB{{efn-ua|name=protection_parameters_table_note_c|Depending on analog TV systems used.}}
| −6&nbsp;dB
|-
! Upper Adjacent Channel DTV into Analog TV
| −12&nbsp;dB
| −11.95&nbsp;dB
| −1 ~ −10{{efn-ua|name=protection_parameters_table_note_c}}
| −5&nbsp;dB
|-
! Lower Adjacent Channel Analog TV into DTV
| −48&nbsp;dB
| −47.33&nbsp;dB
| −34 ~ −37&nbsp;dB{{efn-ua|name=protection_parameters_table_note_c}}
| −35&nbsp;dB
|-
! Upper Adjacent Channel Analog TV into DTV
| −49&nbsp;dB
| −48.71&nbsp;dB
| −38 ~ −36&nbsp;dB{{efn-ua|name=protection_parameters_table_note_c}}
| −37&nbsp;dB
|-
! Lower Adjacent Channel DTV into DTV
| −27&nbsp;dB
| −28&nbsp;dB
| −30&nbsp;dB
| −28&nbsp;dB
|-
! Upper Adjacent Channel DTV into DTV
| −27&nbsp;dB
| −26&nbsp;dB
| −30&nbsp;dB
| −29&nbsp;dB
|}

{{Notelist-ua}}

=== Interaction ===
Viewers can interact and provide data back to broadcasters with DTV systems in various ways shown in the list below. Return path to the broadcaster is possible in post 2020s DTV systems typically via the viewers internet connection. Some DTV systems support [[video on demand]] using a [[communication channel]] localized to a neighborhood rather than a city (terrestrial) or an even larger area (satellite)

# Browse the [[electronic program guide]]. 
# Targeted advertising<ref>{{Cite web |title=Transforming Digital TV Advertising with Interactive ChatGPT Technology: Enhancing User Engagement and Ad Effectiveness. AI Development in Digital TV. ChatGPT in Digital TV developers. |url=https://devset.ai/blog/transforming-digital-tv-advertising-with-interactive-chatgpt-technology-enhancing-user-engagement-and-ad-effectiveness |access-date=2025-07-06 |website=devset.ai}}</ref>
# Viewing statistics<ref>{{Cite web |last=Flack |first=Jason |date=2024-05-09 |title=T.V. Viewing Statistics: Exploring T.V. Viewing Statistics |url=https://greatercollinwood.org/t-v-viewing-statistics-exploring-t-v-viewing-statistics/ |access-date=2025-07-06 |website=Greater Collinwood |language=en-US}}</ref>

== Comparison to analog ==
DTV has several advantages over [[analog television]],

* More efficient bandwidth usage provide more digital channels in the same space and/or provide [[high-definition television]] service
* Digital TV signals require less transmission power than analog TV signals to be broadcast and received satisfactorily.<ref>{{cite web |title=Report ITU-R BT.2140-3 (05/2011) |url=https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2140-3-2011-PDF-E.pdf |url-status=live |archive-url=https://web.archive.org/web/20200610162435/https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2140-3-2011-PDF-E.pdf |archive-date=10 June 2020}}</ref>
* Flexible bandwidth allocations are flexible depending on the level of compression and resolution of the transmitted image. 
* More sound channels. Analog TV began with monophonic sound and later developed [[multichannel television sound]] with two independent audio signal channels. DTV allows up to 5 audio signal channels plus a [[subwoofer]] bass channel, producing broadcasts similar in quality to movie theaters and DVDs.<ref>{{cite web |title=Digital TV: A Cringley Crash Course&nbsp;— Digital Vs. Analog |url=https://www.pbs.org/opb/crashcourse/digital_v_analog/sound.html |url-status=dead |archive-url=https://archive.today/20130713024438/http://www.pbs.org/opb/crashcourse/digital_v_analog/sound.html |archive-date=July 13, 2013 |access-date=2014-01-13 |publisher=Pbs.org}}</ref>
* Can provide for sale of non-television services such as multimedia on demand or interactive purchasing. 
* Permits special services such as multiplexing (more than one program on the same channel), electronic program guides and additional languages (spoken or subtitled). 

Digital and analog signals react to interference differently. For example, common problems with analog television include [[Ghosting (television)|ghosting]] of images, noise from weak signals and other problems that degrade the quality of the image and sound, although the program material may still be watchable. With digital television, because of the [[cliff effect]], reception of the digital signal must be very nearly complete; otherwise, neither audio nor video will be usable.

=== Compression artifacts, picture quality monitoring and allocated bandwidth ===
DTV images have some picture defects not present on analog television or motion picture cinema, because of present-day limitations of bit rate and compression algorithms such as [[MPEG-2]]. This defect is sometimes referred to as [[mosquito noise]].<ref>{{cite web
 | author1=Le Dinh, Phuc-Tue
 | author2=Patry, Jacques
 | url=http://www.videsignline.com/howto/180207350
 | title=Video compression artifacts and MPEG noise reduction
 | work=Video Imaging DesignLine
 | date=February 24, 2006
 | access-date=April 30, 2010
 | archive-date=March 14, 2006
 | archive-url=https://web.archive.org/web/20060314201405/http://www.videsignline.com/howto/180207350
 | url-status=dead
 }}</ref>

Because of the way the human visual system works, defects in an image that are localized to particular features of the image or that come and go are more perceptible than defects that are uniform and constant. However, the DTV system is designed to take advantage of other limitations of the human visual system to help mask these flaws, e.g., by allowing more [[compression artifacts]] during fast motion where the eye cannot track and resolve them as easily and, conversely, minimizing artifacts in still backgrounds that, because time allows, may be closely examined in a scene.

Broadcast, cable, satellite and Internet DTV operators control the picture quality of television signal encoders using sophisticated, neuroscience-based algorithms, such as the [[structural similarity index measure]] (SSIM) video quality measurement tool. Another tool called [[visual information fidelity]] (VIF), is used in the [[Netflix]] [[VMAF]] video quality monitoring system.

Quantising effects can create contours—rather than smooth gradations—on areas with small graduations in amplitude. Typically, a very ''flat'' scene, such as a cloudless sky, will exhibit visible ''steps'' across its expanse, often appearing as concentric circles or ellipses. This is known as [[color banding]]. Similar effects can be seen in very dark scenes, where true black backgrounds are overlaid by dark gray areas. These transitions may be smooth, or may show a ''scattering'' effect as the digital processing dithers and is unable to consistently allocate a value of either absolute black or the next step up the greyscale.

=== Effects of poor reception ===
Changes in signal reception from factors such as degrading antenna connections or changing weather conditions may gradually reduce the quality of analog TV. The nature of digital TV results in a perfectly decodable video initially, until the receiving equipment starts picking up interference that overpowers the desired signal or if the signal is too weak to decode. Some equipment will show a garbled picture with significant damage, while other devices may go directly from perfectly decodable video to no video at all or lock up.<ref>{{Cite web |date=2013-09-25 |title=Digital TV Info |url=https://www.antennadirect.com.au/digital-tv-info/ |access-date=2022-07-22 |website=Antenna Direct |language=en-US}}</ref> This phenomenon is known as the digital cliff effect.<ref>{{Cite web |date=2010-03-01 |title=Steering clear of the digital cliff |url=https://connectedmag.com.au/steering-clear-digital-cliff/ |access-date=2024-01-05 |website=Connected Magazine |language=en-AU}}</ref>

[[Block error]]s may occur when transmission is done with compressed images. A block error in a single frame often results in black boxes in several subsequent frames, making viewing difficult.

For remote locations, distant channels that, as analog signals, were previously usable in a snowy and degraded state may, as digital signals, be perfectly decodable or may become completely unavailable. The use of higher frequencies add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available because usually higher frequency signals can't pass through obstacles as easily.

=== Effect on old analog technology ===
Television sets with only analog tuners cannot decode digital transmissions. When analog broadcasting over the air ceases, users of sets with analog-only tuners may use other sources of programming (e.g., cable, recorded media) or may purchase [[Digital television adapter|set-top converter boxes]] to tune in the digital signals. In the United States, a [[Coupon-eligible converter box|government-sponsored coupon]] was available to offset the cost of an external converter box.

The [[digital television transition]] began around the late 1990s and has been completed on a country-by-country basis in most parts of the world.

=== Disappearance of TV-audio receivers ===
Prior to the conversion to digital TV, analog television broadcast audio for TV channels on a separate FM [[carrier signal]] from the video signal. This FM audio signal could be heard using standard radios equipped with the appropriate tuning circuits.

However, after the [[digital television transition]], no portable radio manufacturer has yet developed an alternative method for portable radios to play just the audio signal of digital TV channels; [[DTV radio]] is not the same thing.

=== Environmental issues ===
The adoption of a broadcast standard incompatible with existing analog receivers has created the problem of large numbers of analog receivers being discarded. One superintendent of public works was quoted in 2009 saying; "some of the studies I’ve read in the trade magazines say up to a quarter of American households could be throwing a TV out in the next two years following the regulation change."<ref>[http://www.tonawanda-news.com/local/local_story_027233552.html North Tonawanda: council discusses future TV disposal] {{Webarchive|url=https://web.archive.org/web/20090131074954/http://tonawanda-news.com/local/local_story_027233552.html |date=2009-01-31 }}, Neale Gulley, Tonawanda News, January 27, 2009</ref> In Michigan in 2009, one recycler estimated that as many as one household in four would dispose of or recycle a TV set in the following year.<ref>[http://detnews.com/apps/pbcs.dll/article?AID=/20090123/METRO/901230383 Trashing the tube: Digital conversion may spark glut of toxic waste], Jennifer Chambers, [[Detroit News]], January 23, 2009</ref> The digital television transition, migration to [[high-definition television]] receivers and the replacement of CRTs with flat screens are all factors in the increasing number of discarded analog CRT-based television receivers. In 2009, an estimated 99 million analog TV receivers were sitting unused in homes in the US alone and, while some obsolete receivers are being retrofitted with converters, many more are simply dumped in landfills where they represent a source of toxic metals such as [[lead]] as well as lesser amounts of materials such as [[barium]], [[cadmium]] and [[chromium]].<ref>[http://www.wltx.com/news/story.aspx?storyid=69896&catid=306 Old Toxic TVs Cause Problems], USA TODAY, January 27, 2009</ref><ref>[http://www.jsonline.com/news/wisconsin/38198929.html Unloading that old TV not quite so simple], Lee Bergquist, [[Milwaukee Journal-Sentinel]], January 23, 2009</ref>

== See also ==
* [[Autoroll]]
* [[Digital television in the United Kingdom]]
* [[Digital television in the United States]]
* [[Text to speech in digital television]]

== References ==
{{Reflist}}

== Further reading ==
* [[Jeffrey A. Hart|Hart, Jeffrey A.]], [https://web.archive.org/web/20120515012604/http://inethub.olvi.net.ua/ftp/library/somelibrary/techno/hart%20j.a.%20-%20technology,%20television%20and%20competition%5Bc%5D%20the%20politics%20of%20digital%20tv%20(2004)(en).pdf ''Television, technology, and competition : HDTV and digital TV in the United States, Western Europe, and Japan''], New York : Cambridge University Press, 2004. {{ISBN|0-521-82624-1}}
* [https://www.researchgate.net/publication/2997973_Overview_of_Digital_Television_Development_Worldwide Overview of Digital Television Development Worldwide] [[Proceedings of the IEEE]], VOL. 94, NO. 1, JANUARY 2006 ([[University of Texas at San Antonio]])

== External links ==
{{Commons category|Digital television}}
* [http://www.dtv.gov/ The FCC's US consumer-oriented DTV website] {{Webarchive|url=https://web.archive.org/web/20110723033548/http://www.dtv.gov/ |date=2011-07-23 }}

{{Digital television deployments}}
{{Broadcasting}}
{{Telecommunications}}
{{Digital electronics}}
{{Authority control}}

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[[Category:Telecommunications-related introductions in the 1990s]]