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Encyclopedia > Digital Television

Digital television (DTV) refers to the sending and receiving of moving images and sound by means of discrete (digital) signals, in contrast to the analog signals used by analog TV. Introduced in the late 1990s, this technology appealed to the television broadcasting business and consumer electronics industries as offering new financial opportunities. Image File history File links This is a lossless scalable vector image. ... Discrete sampled signal Digital signal A discrete signal or discrete-time signal is a time series, perhaps a signal that has been sampled from a continuous-time signal. ... The term digital signal is used to refer to more than one concept. ... Analog television (or analogue television) encodes television and transports the picture and sound information as an analog signal, that is, by varying the amplitude and/or frequencies of the broadcast signal. ...


Digital television is more flexible and efficient than analog television. When properly used by broadcasters, digital television allows higher-quality images and sound and more programming choices than analog does. However, although DTV allows for superior technical quality, a digital signal does not necessarily carry a higher-quality image or sound than an analog signal.

Contents

Technical information

Formats and bandwidth

In current practice, high-definition television (HDTV), which is usually used over DTV, uses one of two formats: 1280 × 720 pixels in progressive scan mode (abbreviated 720p) or 1920 × 1080 pixels in interlace mode (1080i). Each of these utilizes a 16:9 aspect ratio. (Some televisions are capable of receiving an HD resolution of 1920 × 1080 at a 60 Hz progressive scan frame rate — known as 1080p60 — but this format is not standard and no broadcaster is able to transmit these signals over the air at acceptable quality yet.) High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). ... This article is about the picture element. ... Progressive scan Progressive or noninterlaced scanning is any method for displaying, storing or transmitting moving images in which the lines of each frame are drawn in sequence. ... JOHN HERMAN SUCKS FAT DICK ... Interlace is a technique of improving the picture quality of a video signal without consuming any extra bandwidth. ... 1080i is a shorthand name for a category of video modes. ... The 16:9 aspect ratio (also known as widescreen) is an aspect ratio that is 16/9 or 1. ... The aspect ratio of a two-dimensional shape is the ratio of its longer dimension to its shorter dimension. ... 1080p is the shorthand name for a category of display resolutions. ...


Standard definition TV, 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. For 4:3 aspect-ratio broadcasts, the 640 × 480 format is used in NTSC countries, while 720 × 576 (rescaled to 768 × 576) is used in PAL countries. For 16:9 broadcasts, the 704 × 480 (rescaled to 848 × 480) format is used in NTSC countries, while 720 × 576 (rescaled to 1024 × 576) is used in PAL countries. However, broadcasters may choose to reduce these resolutions to save bandwidth (e.g., many DVB-T channels in the United Kingdom use a horizontal resolution of 544 or 704 pixels per line).[1] The perceived quality of such programming is surprisingly acceptable because of interlacing—the effective vertical resolution is halved to 288 lines. 4:3 is a ratio. ... NTSC is the analog television system in use in Canada, Japan, Mexico, the Philippines, South Korea, Taiwan, the United States, and some other countries, mostly in the Americas (see map). ... For other uses, see PAL (disambiguation). ... The 16:9 aspect ratio (also known as widescreen) is an aspect ratio that is 16/9 or 1. ...


Each DTV channel is permitted to be broadcast at a data rate up to 19 megabits per second, or 2.375 megabytes per second. However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead the broadcast can be subdivided across several video subchannels of varying quality and compression rates, including non-video datacasting services that allow one-way high-bandwidth streaming of data to computers. Datacasting (data broadcasting) is the broadcasting of data over a wide area via radio waves. ...


A broadcaster may opt to use a standard-definition digital signal instead of an HDTV signal, because current convention allows the bandwidth of a DTV channel (or "multiplex") to be subdivided into multiple subchannels, providing multiple feeds of entirely different programming 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 (or "stat-mux"). 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 bitrate and make reception easier for more distant or mobile viewers. A multiplex (called virtual sub-channel in the United States and Canada) is a group of digital TV channels that are mixed together for broadcast. ... Digital television in the United States supports multiple digital subchannels if you divide the 19. ... A Statistical Multiplexer allows broadcasters to change the bitrate of channels according to the channels needs. ... DVB-T stands for Digital Video Broadcasting - Terrestrial and it is the DVB European consortium standard for the broadcast transmission of digital terrestrial television. ... In telecommunications and computing, bitrate (sometimes written bit rate, data rate or as a variable Rbit) is the number of bits that are conveyed or processed per unit of time. ...


Reception

There are a number of different ways to receive digital television. One of the oldest means of receiving DTV (and TV in general) is using an antenna (known as an aerial in some countries). This way is known as Digital Terrestrial Television (DTT). With DTT, viewers are limited to whatever channels the antenna picks up. Signal quality will also vary. A Yagi-Uda beam antenna Short Wave Curtain Antenna (Moosbrunn, Austria) A building rooftop supporting numerous dish and sectored mobile telecommunications antennas (Doncaster, Victoria, Australia) An antenna is a transducer designed to transmit or receive radio waves which are a class of electromagnetic waves. ... Digital Terrestrial Television (DTTV or DTT) is an implementation of digital technology to provide a greater number of channels and/or better quality of picture and sound using aerial broadcasts to a conventional antenna (or aerial) instead of a satellite dish or cable connection. ...


Other ways have been devised to receive digital television. Among the most familiar to people are digital cable and digital satellite. In some countries where transmissions of TV signals are normally achieved by microwaves, digital MMDS is used. Other standards, such as DMB and DVB-H, have been devised to allow handheld devices such as mobile phones to receive TV signals. Another way is IPTV, that is receiving TV via Internet Protocol with guaranteed quality of service (QoS). Finally, an alternative way is to receive TV signals via the open Internet infra-structure, usually referred to as Internet TV. Digital cable is a term for a type of cable digital television that delivers more channels than possible with analog cable by using digital video compression. ... Artists impression of a Boeing 601 satellite, as configured for digital television transmission by SES Astra Satellite television is television delivered by way of communications satellites, as compared to conventional terrestrial television and cable television. ... Microwave Slang for small waves, like at a beach, often used by surfers. ... Multichannel multipoint distribution service, also known as MMDS or wireless cable, is a wireless telecommunications technology, used for general-purpose broadband networking or, more commonly, as an alternative method of cable television programming reception. ... Digital Multimedia Broadcasting (DMB) is a digital radio transmission system for sending multimedia (radio, TV, and datacasting) to mobile devices such as mobile phones. ... DVB-H (Digital Video Broadcasting - Handheld) is one of three prevalent mobile TV formats. ... A stylised representation of a mobile phone A mobile phone is a device which behaves as a normal telephone whilst being able to move over a wide area ( cordless phone which acts as a telephone only within a limited range). ... This article is about internet protocol television. ... This article does not cite any references or sources. ...


Today, regardless of how viewers receive DTV, most will pick up digital television via a set-top box, which decodes the digital signals into signals that analog televisions can understand — thus using the television purely as a monitor. However, a growing number of TV sets with integrated receivers are available — these are known as iDTVs. A Digitrax DH163AT DCC decoder in an Athearn locomotive before the shell goes on. ...


Some signals carry encryption and specify use conditions (such as "may not be recorded" or "may not be viewed on displays larger than 1 m in diagonal measure") backed up with the force of law under the WIPO Copyright Treaty and national legislation implementing it, such as the U.S. Digital Millennium Copyright Act. Access to encrypted channels can be controlled by a removable smart card, for example via the Common Interface (DVB-CI) standard for Europe and via Point Of Deployment (POD) for IS or named differently CableCard. Encrypt redirects here. ... The WIPO Copyright Treaty, adopted by the World Intellectual Property Organization (WIPO) in 1996, provides additional protections for copyright deemed necessary in the modern information era. ... Legislation (or statutory law) is law which has been promulgated (or enacted) by a legislature or other governing body. ... The Digital Millennium Copyright Act (DMCA) is a United States copyright law which implements two 1996 WIPO treaties. ... Smart card used for health insurance in France. ... DVB, short for Digital Video Broadcasting, is a suite of internationally accepted, open standards for digital television maintained by the DVB Project, an industry consortium with more than 300 members, and published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC... CableCARD is a plug-in card approximately the size of a credit card that allows consumers in the United States to view and record digital cable television channels on digital video recorders, personal computers and televisions without the use of other equipment such as a set top box (STB) provided...


Protection parameters for terrestrial DTV broadcasting

[clarify]

System Parameters
(protection ratios)
Canada [13] USA [5] EBU [9, 12]
ITU-mode M3
Japan & Brazil [36, 37][2]
C/N for AWGN Channel +19.5 dB
(16.5 dB[3])
+15.19 dB +19.3 dB +19.2 dB
Co-Channel DTV into Analog TV +33.8 dB +34.44 dB +34 ~ 37 dB +38 dB
Co-Channel Analog TV into DTV +7.2 dB +1.81 dB +4 dB +4 dB
Co-Channel DTV into DTV +19.5 dB
(16.5 dB[3])
+15.27 dB +19 dB +19 dB
Lower Adjacent Channel DTV into Analog TV −16 dB −17.43 dB −5 ~ −11 dB[4] −6 dB
Upper Adjacent Channel DTV into Analog TV −12 dB −11.95 dB −1 ~ −10[4] −5 dB
Lower Adjacent Channel Analog TV into DTV −48 dB −47.33 dB −34 ~ −37 dB[4] −35 dB
Upper Adjacent Channel Analog TV into DTV −49 dB −48.71 dB −38 ~ −36 dB[4] −37 dB
Lower Adjacent Channel DTV into DTV −27 dB −28 dB −30 dB −28 dB
Upper Adjacent Channel DTV into DTV −27 dB −26 dB −30 dB −29 dB

Interaction

Interaction happens between the TV watcher and the DTV system. It can be understood in different ways, depending on which part of the DTV system is concerned. It can be an interaction with the STB only (to tune to another TV channel or to browse the EPG). The Sky Digital EPG in the United Kingdom and Republic of Ireland. ...


Modern DTV systems are able to provide interaction between the end-user and the broadcaster through the use of a return path. With the exceptions of coaxial and fiber optic cable, which can be bidirectional, a dialup modem, Internet connection, or other method is typically used for the return path with unidirectional networks such as satellite or antenna broadcast.


In addition to not needing a separate return path, cable also has the advantage of a communication channel localized to a neighborhood rather than a city (terrestrial) or an even larger area (satellite). This provides enough customizable bandwidth to allow true video on demand. A Communications channel (or channel for short), models the medium through which information is transmitted from a sender (or transmitter) to a receiver. ... Video on demand (VOD) systems allow users to select and watch video and clip content over a network as part of an interactive television system. ...


Advantages to conversion

DTV has several advantages over analog TV, the most significant being that digital channels take up less bandwidth (and the bandwidth needs are continuously variable, at a corresponding cost in image quality depending on the level of compression). This means that digital broadcasters can provide more digital channels in the same space, provide high-definition television service, or provide other non-television services such as multimedia or interactivity. DTV also permits special services such as multiplexing (more than one program on the same channel), electronic program guides and additional languages, spoken or subtitled. The sale of non-television services may provide an additional revenue source. In many cases, viewers perceive DTV to have superior picture quality, improved audio quality, and easier reception than analog. High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). ...


Disadvantages to conversion

Impact on existing analog technology

The analog switch-off ruling, which so far has met with little opposition from consumers or manufacturers, would render all non-digital televisions obsolete on the switch-off date, unless connected to an external off-the-air tuner, analog or digital cable, or a satellite system. An external converter box (an ATSC tuner) can be added to non-digital televisions to lengthen their useful lifespan. Several of these devices have already been shown and, while few were initially available, they are becoming more available by the day. Once connected to the converter unit, operation of non-digital units is seamless and, in most cases, rich in new features (in comparison to previous analog reception operation). In the US, the federal government supports the adoption of digital converters through the mailing of coupons, which cover around 80% of the cost of each unit. Advance Television Systems Committe (ATSC) tuner allows reception of over the air high definition digital television signals in North America and South Korea. ...


Some existing analog equipment will be less functional with the use of a converter box. For example, television remote controls will no longer be effective at changing channels, because that function will instead be handled by the converter box. Similarly, video recorders for analog signals (including both tape-based VCRs and hard-drive-based DVRs) will not be able to select channels, limiting their ability to automatically record programs via a timer or based on downloaded program information. Also, older, handheld televisions, which rely primarily on over-the-air signals, and battery operation, will be rendered impractical, since the proposed converter boxes are not portable, nor powered with batteries. Portable radios which feature the ability to listen to television audio on VHF channels 2-13 would also lose their ability to function, while television stations which formerly broadcast on Channel 6 and were able to have their analog audio heard on common radios using a quirk in the system where their audio could be heard on the far end of the FM band at 87.7, would lose the ability for commuters to listen to their broadcasts. The video cassette recorder (or VCR, less popularly video tape recorder) is a type of video tape recorder that uses removable cassettes containing magnetic tape to record audio and video from a television broadcast so it can be played back later. ... Foxtel IQ, a digital video recorder and a satellite cable set-top box. ... The personal stereo is the term given to a portable audio player using an audiocassette player. ... In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency. ...


If new TVs contain only an ATSC tuner, it prevents older devices, such as VCRs and video game consoles with only an analog RF output, from connecting to the TV. Connection would require an analog to digital converter box, which is the opposite as what is currently being sold. Such a box would also likely introduce additional delay into the video signal.


Compression artifacts and allocated bandwidth

DTV images have some picture defects that are not present on analog television or motion picture cinema, because of present-day limitations of bandwidth and compression algorithms such as MPEG-2. MPEG-2 is a standard for the generic coding of moving pictures and associated audio information [1]. It is widely used around the world to specify the format of the digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. ...


When a compressed digital image is compared with the original program source, some hard-to-compress image sequences may have digital distortion or degradation. For example:

  • quantization noise,
  • incorrect color,
  • blockiness,
  • a blurred, shimmering haze.

Broadcasters attempt to balance their needs to show high quality pictures and to generate revenue by using a fixed bandwidth allocation for more services.


Buffering and preload delay

Unlike analog televisions, digital televisions have a significant delay when changing channels, making "channel surfing" more difficult.


Different devices need different amounts of preload time to begin showing the broadcast stream, resulting in an undesirable and annoying audio echo effect when two televisions in adjacent rooms of a house are tuned to the same channel.


Effects of poor reception

Changes in signal reception from factors such as degrading antenna connections or worsening weather conditions may gradually reduce the quality of analog TV. However, the nature of digital TV results in a perfect picture, until the receiving equipment is completely unable to generate a picture at all. This is known as the digital cliff or cliff effect. In telecommunications, the cliff effect or digital cliff describes the sudden loss of digital signal reception. ...


For remote locations, distant analog channels that were previously acceptable in a snowy and degraded state may either display perfectly, or be completely unavailable.


Hype vs reality of picture quality

Making the switch from analog to digital will provide television viewers with the potential for a movie-quality picture, and better HD for those who own an HDTV, but initially broadcasters are transmitting mostly low-definition, non-widescreen 480i digital version of most of their content.


Limitations

The greatest DTV detail level currently available is 1080i, which is a 1920x1080 interlaced widescreen format. Interlacing is done to reduce the image bandwidth to one-half of full-frame quality, which gives better frame update speed for quick-changing scenes such as sports, but at the same time reduces the overall image quality and introduces image flickering and crawling scanlines because of the alternating field refresh.


Full-frame progressive-scan 1920x1080 (1080p) requires up to twice the data bandwidth currently available in the DTV channel specification. 1080p may become an option in the future, as image compression algorithms improve, allowing more detail to be sent via the same channel bandwidth allocations to be used now.


The limitations of interlacing can be partially overcome through the use of advanced image processors in the consumer display device, such as the use of Faroudja DCDi and using internal framebuffers to eliminate scanline crawling. DCDi (Directional Correlation Deinterlacing) is a digital enhancement method for improving image quality on low resolution images. ...

See also

Television Portal

Image File history File links Portal. ... The transition to digital television is a process that follows different paces around the world. ... ATSC redirects here. ... Advance Television Systems Committe (ATSC) tuner allows reception of over the air high definition digital television signals in North America and South Korea. ... There are several broadcast television systems in use in the world today. ... This article needs to be cleaned up to conform to a higher standard of quality. ... DVB-T stands for Digital Video Broadcasting - Terrestrial and it is the DVB European consortium standard for the broadcast transmission of digital terrestrial television. ... DMB-T/H or DTMB (GB 20600-2006) is the Peoples Republic of Chinas (PRC) terrestrial digital television standard and will cover fixed and mobile terminals. ... Siemens has the following uses: Siemens is a German family name carried by generations of the telecommunications industrialists, including Werner von Siemens, Sir William Siemens, Wilhelm von Siemens and Peter von Siemens Siemens AG is a German electrical and telecommunications company, founded as a telegraph equipment manufacturer by Werner von... High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). ... Digital TV set-top box Interactive television describes a number of techniques which allow viewers to interact with television content as they view it. ... Integrated Services Digital Broadcasting (ISDB) is the digital television (DTV) and digital audio broadcasting (DAB) format. ... The LinuxTV project is an informal group of volunteers who develop software related to digital television for the Linux operating system. ... Multimedia Home Platform (DVB-MHP) is an open middleware system standard designed by the DVB project for interactive digital television. ... Zapper may refer to: NES Zapper, a pistol-shaped electronic light gun sold as part of the original Nintendo Entertainment System Zapper: One Wicked Cricket, a multi-platform video game released in 2002 A TDT or satellite tuner, without MHP (this last, generally includes IPTV return channel, i. ... A set-top box (STB) or set-top unit (STU) is a device that connects to a television and an external source of signal, turning the signal into content which is then displayed on the television screen. ... System-on-a-chip (SoC or SOC) is an idea of integrating all components of a computer system into a single chip. ... This article or section is in need of attention from an expert on the subject. ... Digital switchover is the name given to the process in which analogue broadcast television in an area is converted to digital television. ...

References

  1. ^ [http://dtt.me.uk Latest snapshots - Freeview/DTT bitrates (Mendip transmitter, UK)
  2. ^ ISDB-T (6 MHz, 64QAM, R=2/3), Analog TV (M/NTSC).
  3. ^ a b The Canadian parameter, C/(N+I) of noise plus co-channel DTV interface should be 16.5 dB.
  4. ^ a b c d Depending on analog TV systems used.

External links


  Results from FactBites:
 
Digital television - Wikipedia, the free encyclopedia (1343 words)
Digital television (DTV) is a telecommunication system for broadcasting and receiving moving pictures and sound by means of digital signals, in contrast to analog signals in analog (traditional) TV.
It uses digital modulation data, which is digitally compressed and requires decoding by a specially designed television set or a standard receiver with a set-top box.
All early SDTV television standards were analog in nature, and SDTV digital television systems derive much of their structure from the need to be compatible with analog television.
  More results at FactBites »

 
 

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