Editing Digital television (section)

== 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. 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. 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 make reception easier 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 signals are protected by [[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]]. Access to encrypted channels can be controlled by a removable card, for example via the [[Common Interface]] or [[CableCard]].

=== Protection parameters ===
Digital television signals must not interfere with each other and they must also 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 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 ===
People can interact with a DTV system in various ways. One can, for example, browse the [[electronic program guide]]. Modern DTV systems sometimes use a return path providing feedback from the end user to the broadcaster. This is possible over cable TV or through an Internet connection but is not possible with a standard antenna alone.

Some of these systems support [[video on demand]] using a [[communication channel]] localized to a neighborhood rather than a city (terrestrial) or an even larger area (satellite).

=== 1seg ===
[[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.