Digital television

Digital television (DTV) is 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.

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 a digital signal does not necessarily carry a higher-quality image or sound than an analog signal.

Technical information

Formats and bandwidth

With digital television, two formats--HDTV and SDTV--of TV programme are broadcast.

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.)

Standard definition TV(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. 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.

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.

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.

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.

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, relying on DSL or optical cable line. Finally, an alternative way is to receive digital TV signals via the open Internet. For example, there is a lot of P2P Internet Television software that can be used to watch TV on your computer.

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.

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).

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.

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.

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 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 achievable and, in most cases, rich in new features (in comparison to previous analog reception operation). At present, analog switchoff is scheduled for February 17, 2009 in the United States and August 31, 2011 in Canada.

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. ATSC-capable VCRs are likely to be far less common than their NTSC counterparts, with most current offerings being VCR/DVD combo units. 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 this ability, while television stations which formerly broadcast on Channel 6 (with analog FM audio on 87.75 MHz) would no longer be heard on standard FM broadcast band radios. These stations would lose the ability for commuters to listen to their broadcasts.

Were any new TVs to contain only an ATSC tuner, this could prevent 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. Fortunately, analog inputs suitable for connection to VCRs have remained available on all current digital-capable TV's.

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.
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. The nature of digital TV results in a perfect picture initially, until the receiving equipment starts picking up noise or losing signal. Some equipment will show a picture even with significant damage, while other devices may go directly from perfect to no picture at all (and thus not show even a slightly damaged picture). This latter effect is known as the digital cliff or cliff effect.

For remote locations, distant analog channels that were previously acceptable in a snowy and degraded state may be anything from perfect to completely unavailable. The use of lower power (typically one-fifth that of analog broadcasts in the US) and higher frequencies will add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available. Many intermittent signal fading conditions, such as the rapid-fade effect caused by reflections of UHF television signals from passing aircraft, will produce not intermittently-snowy video but potential intermittent loss of the entire signal.

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.

Surround sound

Multichannel audio denominates the techniques for enriching (expanding and deepening) the sound reproduction quality, of a recorded source, with additional, recorded sound channels reproduced via additional, discrete speakers. The three-dimensional (3D) sphere of human hearing can be virtually achieved with audio channels above and below the listener. To that end, the multichannel surround sound application encircles the audience (left-surround, right-surround, back-surround), as opposed to "screen channels" (center, [front] left, and [front] right), i.e. ca. 360° horizontal plane, 2D).

The first, documented use of surround sound was in 1940, for the Disney studio's animated film Fantasia. Its multichannel audio application was called 'Fantasound', comprising three audio channels and speakers; the sound was diffused throughout the cinema, initially, by an engineer using some 54 loudspeakers; the surround sound was achieved using the sum and the difference of the phase of the sound.

Surround sound technology is used in both cinema and "home theater" systems, video game consoles, and personal computers, et cetera. Commercial surround sound formats include videocassettes, Video DVDs, and HDTV broadcasts encoded as Dolby Pro Logic, Dolby Digital, or DTS. Other commercial formats include the competing DVD-Audio (DVD-A) and Super Audio CD (SACD) formats; and MP3 Surround. Cinema 5.1 surround formats include Dolby Digital, DTS, and Sony Dynamic Digital Sound (SDDS).

Mostly, film production companies and video game creators are the principal users of surround sound; however, some consumer camcorders have such capability, either in-built or discrete. Some AV receivers, stereophonic systems, and computer soundcards contain integral digital signal processors and / or digital audio processors to simulate surround sound from a stereophonic source.

Creating surround sound

Surround sound is created several ways. The first, and simplest, method is using a surround sound recording microphone technique and / or mixing-in surround sound for playback on an audio system using speakers — encircling the listener — to play audio from different directions. A second approach is processing the audio with psychoacoustic sound localization methods to simulate a two-dimensional (2-D) sound field with headphones. A third approach, based on Huygens' principle, attempts reconstructing the recorded sound field wavefronts within the listening space, an "audio hologram" form. One form, wave field synthesis (WFS), produces a soundfield with an even error field over the entire area. Commercial WFS systems, made by the Swiss companies sonic emotion and Iosono, require a many loudspeakers and much computing power.

The Ambisonics form, also based on Huygens' principle, gives an exact sound reconstruction at the central point; less accurate away from center point. There are many free and commercial software available for Ambisonics, which dominates most of the consumer market, especially musicians using electronic and computer music. Moreover, Ambisonics products are the standard in surround sound hardware sold by Meridian Audio, Ltd. In its simplest form, Ambisonics consumes few resources, however, this is not true for recent developments, such as Near Field Compensated Higher Order Ambisonics. Some years ago it was shown that, in the limit, WFS and Ambisonics converge.

Finally, surround sound also can be achieved by mastering level, from stereophonic sources as with Penteo, which uses FFT analysis of a stereo recording to break individual sounds to component panorama positions, then positions them, accordingly, into a five-channel field.

Mapping channels to speakers

In most cases, surround sound systems rely on the mapping of each source channel to its own loudspeaker. Matrix systems recover the number and content of the source channels and apply them to their respective loudspeakers. With discrete surround sound, the transmission medium allows for (at least) the same number of channels of source and destination; however, one-to-one, channel-to-speaker, mapping is not the only way of transmitting surround sound signals.

The transmitted signal might encode the information (defining the original sound field) to a greater or lesser extent; the surround sound information is rendered for replay by a decoder generating the number and configuration of loudspeaker feeds for the number of speakers available for replay. This "replay device independent" encoding is analogous to encoding and decoding an Adobe PostScript file, where the file describes the page, and is rendered per the output device's resolution capacity. The Ambisonics and WFS systems use audio rendering; the Meridian Lossless Packing contains elements of this capability.

Bass management

Surround replay systems may make use of bass management, the fundamental principle of which is that bass content in the incoming signal, irrespective of channel, should be directed only to loudspeakers capable of handling it, whether the latter are the main system loudspeakers or one or more special low-frequency speakers called subwoofers.

There is a notation difference before and after the bass management system. Before the bass management system there is a Low Frequency Effects (LFE) channel. After the bass management system there is a subwoofer signal. A common misunderstanding is the belief that the LFE channel is the "subwoofer channel". The bass management system may direct bass to one or more subwoofers (if present) from any channel, not just from the LFE channel. Also, if there is no subwoofer speaker present then the bass management system can direct the LFE channel to one or more of the main speakers.

Low Frequency Effects (LFE) channel

The Low Frequency Effects channel, or LFE, is a source of some confusion in surround sound. The LFE channel was originally developed to carry extremely low "sub-bass" cinematic sound effects (e.g., the loud rumble of thunder or explosions) on their own channel. When loud sub-bass effects are on a different channel, this allows theaters to control the volume of the sub-bass effects, so that it suits the size of their sound reproduction system and the acoustic environment of their cinema. Independent control of the sub-bass effects also reduced the problem of intermodulation distortion in analog movie sound reproduction.

In the original movie theater implementation, the LFE was a separate channel fed to one or more subwoofers. However, home replay systems may not have a separate bass speaker (subwoofer) that is able to handle the sub-bass effects. As a result, modern home surround decoders and systems often include a bass management system that allows bass on any channel (main or LFE) to be fed only to the loudspeakers that can handle low-frequency signals. The salient point here is that the LFE channel is not the "subwoofer channel"; there may not even be a subwoofer, and if there is it may be handling a good deal more than effects.

Some record labels such as Telarc and Chesky have argued that LFE channels are not needed in a modern digital multichannel entertainment system. They argue that all available channels have a full frequency range and, as such, there is no need for an LFE in surround music production, because all the frequencies are available in all the main channels. These labels sometimes use the LFE channel to carry a height channel, underlining its redundancy for its original purpose.

LFE is sometimes expanded as Low-frequency Enhancment.

Surround sound specifications

The descriptions of surround sound specifications below distinguish between the number of discrete channels encoded in the original signal and the number of channels reproduced for playback. The number of channels reproduced for playback can be changed by using matrix decoding. A distinction is also made between the number of channels reproduced for playback and the number of speakers used to reproduce (each channel may refer to a group of speakers). The graphics to the right of each specification description represent the number of channels, not the number of speakers.

3.0 Channel Surround (analog matrixed: Dolby Surround)

Extracts 3 audio channels from a specially encoded two-channel source:Two channels for speakers at the front—left (L) and right (R).One channel for surround speaker or speakers at the rear—surround (S).Describes the numerous matrixed (pre- Pro Logic) surround processors.

Placement: (three speakers in total) Three identical speakers placed equidistant around a central listening position. If two rear speakers are used they should also be placed at ear height, slightly behind the listening position, and should be of bi-polar construction.

4.0 Channel Surround (analog matrixed/discrete: Quadraphonic)

Extracts four audio channels from either a specially encoded two-channel source or a four-channel source:Two channels for speakers at the front—left (L) and right (R).Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).Describes the early matrixed systems and discrete Quadraphonic surround systems. Source media, usually LP record or tape, is often branded four channel stereo.

Placement: Quadraphonics is a system designed for music only. All speakers should be at an ±45˚. All speakers should be at ear height.

4.0 Channel Surround (analog matrixed: Dolby Pro Logic)

Extracts four audio channels from a specially encoded two-channel source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).One channel for both surround speakers at the rear—mono surround channel (S).Describes the Dolby Pro Logic matrixed surround system. Source media, usually VHS, Laser Disc, television broadcast or CableTV/Satellite is often branded with "Dolby Surround" logo. This is the encoding used on the analog optical track for theatrical motion picture films.

Placement: (Five speakers in total) The front speakers should be placed at the edges of the screen, toed in to face the central listening location, and the tweeters should be ear height. The center speaker should be placed behind the screen (when using projection) or over or under a TV, and as close to ear-high as possible. Surround channel speakers should be placed at ear height, slightly behind the listening position, and should be of bi-pole construction.

5.1 Channel Surround (3-2 Stereo) (analog matrixed: Dolby Pro Logic II)

Extracts Five audio channels from either a specially encoded two-channel or a stereo source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).One low-frequency effects channel (LFE).Describes the Dolby Pro Logic II matrixed surround system. Source media is often gaming systems including Playstation 2, GameCube and Wii games branded with "Pro Logic II" logo.

5.1 surround sound may also be referred to as 3-2 stereo. This defines the configuration that has been standardised for numerous surround sound applications. The term 3-2 refers to 3 front speakers and 2 rear speakers.
Placement: 5.1 speaker layouts should conform to the ITU-R BS.775 standard, despite the myth that music and video content require different placements. The ITU standard states that the left and right speakers are located at ±30˚, while the rear speakers should be positioned approximately ±110˚. There is speculation that rear loudspeakers at ±150˚ provide "more exciting surround effects".

5.1 Channel Surround (70 mm 6-Track) (analog magnetic)

Delivers six audio channels from a 6 channel source:Four channels for speakers at the front-left (L), left center (LC), right center (RC), and right (R).One channel for speaker at the center-center (C)One channel for surround speaker at the rear-monaural surround (S).

5.1 Channel Surround (3-2 Stereo) (analog magnetic: Dolby Stereo "Baby Boom")

Delivers five audio channels and 1 LFE channel from a 6 channel source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).One low-frequency effects channel (LFE).

5.1 Channel Surround (3-2 Stereo) (digital discrete: Dolby Digital, DTS, SDDS)

Delivers Five discrete audio channels and 1 LFE channel from a 6 channel source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).One low-frequency effects channel (LFE).Describes the Dolby Digital, Digital Theater System (DTS), and Sony Dynamic Digital Sound (SDDS) systems. Source media, usually DVD and sometimes Laser Disc or satellite/digital cable is often branded with "Dolby Digital" and/or DTS logos.DTS uses a higher data rate than Dolby Digital, so DTS can achieve higher fidelity.

5.1 surround sound may also be referred to as 3-2 stereo. This defines the configuration that has been standardised for numerous surround sound applications. The term 3-2 refers to 3 front speakers and 2 rear speakers.

Placement: 5.1 speaker layouts should conform to the ITU-R BS.775 standard, despite the myth that music and video content require different placements. The ITU standard states that the left and right speakers are located at ±30˚, while the rear speakers should be positioned approximately ±110˚. There is speculation that rear loudspeakers at ±150˚ provide "more exciting surround effects".

6.1 Channel Surround (analog matrixed: Dolby Pro Logic IIx)

Extracts six audio channels and one low-frequency channel from either a specially encoded two-channel or stereo source. Expands a back surround channel from a 5.1 channel source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).Two channels for surround speakers at the sides—side left (LS) and side right (RS).One channel for surround speakers at the rear—back surround channel (BS).One low-frequency channel to drive a sub-woofer.Describes the Dolby Pro Logic IIx matrixed surround system. Source media is the same as both Dolby Pro Logic and Dolby Pro Logic II.

Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location. The center speaker should be placed behind the screen (when using projection) or over or under a TV. Side channel speakers should be placed to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed slightly behind the listening position, and should have a normal high-quality monopolar construction. All speakers should be at ear height.

6.1 Channel Surround (digital partially discrete: Dolby Digital EX)

Delivers five audio channels, one extracted audio channel and one LFE channel from a six channel source:Two discrete channels for speakers at the front—left (L) and right (R).One discrete channel for speaker at the center—center (C).Two channels for surround speakers at the sides—left surround (LS) and right surround (RS). The discrete LS and RS channels are dematrixed into LS, RS, and back surround (BS).One channel for surround speakers at the rear—back surround channel (BS).One low-frequency effects channel (LFE).Describes the Dolby Digital EX discrete/matrixed hybrid Surround system. Source media, usually DVD is often branded with "Dolby Digital EX" logo. This format is used in some theatrical motion picture films.

Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location. The center speaker should be placed behind the screen (when using projection) or over or under a TV. Side channel speakers should be placed to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed slightly behind the listening position, and should have a normal high-quality monopolar construction. All speakers should be at ear height.

6.1 Channel Surround (digital discrete: DTS-ES)

Delivers six discrete audio channels and 1 LFE channel from a seven channel source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).Two channels for surround speakers at the sides—side left (LS) and side right (RS).One channel for surround speakers at the rear—back surround channel (BS).One low-frequency effects channel (LFE).Describes the DTS ES discrete Surround system. Source media, usually DVD is often branded with "DTS ES" logo. In theatrical motion picture film, this format does not exist, and the name "DTS-ES" refers to the above hybrid format used for Dolby Digital EX.

Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location. The center speaker should be placed behind the screen (when using projection) or over or under a TV. Side channel speakers should be placed to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed slightly behind the listening position, and should have a normal high-quality monopolar construction. All speakers should be at ear height.

7.1 Channel Surround (digital discrete: Dolby Digital Plus, DTS-HD, Dolby TrueHD)

Delivers seven audio channels and one LFE channel from an 8 channel source:Two channels for speakers at the front—left (L) and right (R).One channel for speaker at the center—center (C).Two channels for surround speakers at the sides—left surround (LS) and right surround (RS).[9]Two channels for surround speakers at the rear—left back (LB) and right back (RB).One low-frequency effects channel (LFE).Describes the Dolby Digital Plus discrete Surround system. Source media, usually HD DVD and sometimes Blu-Ray is often branded with "Dolby Digital Plus" and/or "DTS-HD" logos.

Layout variation for 7.1 widescreen cinema format:Four channels for speakers at the front—left (L), Center-left (CL), right (R) and Center-Right (CR).One channel for speaker at the center—center (C).Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).One low-frequency effects channel (LFE).

This variation is becoming increasingly popular in home entertainment systems, as well as for large cinema auditoria where the screen width is such that the additional channels are needed to cover all angles between the loudspeakers satisfactorily for all seats in the auditorium.

For music, speaker placement is unknown.
Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location, and the tweeters should be ear height. The center speaker should be placed behind the screen (when using projection) or over or under a TV, and as close to ear height as possible. Side channel speakers should be placed on side walls, to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed on side walls, slightly behind the listening position, and should have a normal high-quality monopolar construction.

10.2 Channel SurroundMain article: 10.2

10.2 is the surround sound format developed by THX creator Tomlinson Holman of TMH Labs and University of Southern California (schools of Cinema/Television and Engineering). Developed along with Chris Kyriakakis of the USC Viterbi School of Engineering, 10.2 refers to the format's promotional slogan: "Twice as good as 5.1". Advocates of 10.2 argue that it is the audio equivalent of IMAX.

10.2 augments the LS (left surround) and RS (right surround) channels by two point surround channels that can more finely manipulate sound—allowing the mixer to shift sounds in a distinct 360° circle around the movie watcher.

The 14 discrete channels are:
- Five front speakers: Left Wide, Left, Center, Right and Right Wide

- Five surround channels: Left Surround Diffuse, Left Surround Direct, Back Surround, Right Surround Diffuse and Right Surround Direct

- Two LFE channels: LFE Left, LFE Right

-Two Height channels: Left Height, Right Height

The .2 of the 10.2 refers to the addition of a second subwoofer. The system is bass managed such that all the speakers on the left side use the left sub and all the speakers on the right use the right sub. The Center and Back Surround speaker are split among the two subs. The two subs also serve as two discrete LFE (Low Frequency Effects) channels. Although low frequencies are not localizable, it was found that splitting the bass on either side of the audience increases the sense of envelopment.

22.2 Channel Surround

22.2 is the surround sound component of Ultra High Definition Video (Super Hi-vision TV with 4320 scanning lines), and has been developed by NHK Science & Technical Research Laboratories. As its name suggests, it uses 24 speakers. These are arranged in three layers: A middle layer of ten speakers, an upper layer of nine speakers, and a lower layer of three speakers and two sub-woofers. The system was demonstrated at Expo 2005, Aichi, Japan, the NAB 2006 conference, Las Vegas, and at IBC 2006, Amsterdam, Netherlands.

Infinite Channel Surround (Ambisonics)

Ambisonics is a series of recording and replay techniques using multichannel mixing technology that can be used live or in the studio. Any number of speakers in any physical arrangement can be used to recreate a sound field. With 6 or more speakers arranged around a listener, a 3-dimensional ("periphonic", or full-sphere) sound field can be presented. Ambisonics was invented by Michael Gerzon (among other researchers) of the Mathematical Institute, Oxford.

Panor-Ambiophonic (PanAmbio) 4.0/4.1Main article: Ambiophonics

PanAmbio combines a stereo dipole and crosstalk cancellation in front and a second set in back of the listener (total of four speakers) for 360° 2D surround reproduction. Four channel recordings, especially those containing binaural cues, create speaker-binaural surround sound. 5.1 channel recordings, including movie DVDs, are compatible by mixing C-channel content to the front speaker pair. 6.1 can be played by mixing SC to the back pair.

Notation

This notation, e.g. "5.1", reflects the number of full range channels; including a ".1" to reflect the limited range of the LFE channel.

E.g. 5 full-range channels + 1 LFE channel = 5.1
It can also be expressed as the number of full-range channels in front of the listener, separated by a slash from the number of full-range channels beside or behind the listener, separated by a decimal point from the number of limited-range LFE channels.

E.g. 3 front channels + 2 side channels + an LFE channel = 3/2.1

This notation can then be expanded to include the notation of Matrix Decoders. Dolby Digital EX, for example, has a sixth full-range channel incorporated into the two rear channels with a matrix. This would be expressed:
3 front channels + 2 rear channels + 3 channels reproduced in the rear in total + 1 LFE channel = 3/2:3.1

Note: The term stereo, although popularised in reference to two channel audio, can also be properly used to refer to surround sound, as it strictly means "solid" sound. However this is no longer a common usage and "stereo sound" is almost exclusively used to describe two channel left and right sound.

Dolby Pro Logic

Dolby Pro Logic is a surround sound processing technology designed to decode soundtracks encoded with Dolby Surround. Dolby Surround Stereo was originally developed by Dolby Laboratories in 1976 for analog cinema sound systems. The format was adapted for home use in 1982 as Dolby Surround when HiFi capable consumer VCRs were earlier introduced and was then replaced by the newer and improved Pro Logic system in 1987. However, the term "Dolby Surround" is still used to describe the encoding technology or matrix-encoded soundtrack, whereas Pro Logic refers to the decoding technology/processor. It is the domestic equivalent of the theatrical Dolby Stereo technology used in movie cinemas in the 1970s and '80s. The two technologies are mostly identical but a change in marketing was needed so as not to confuse cinema stereo which is at least four channels of audio with home stereo which is only two. Thus Dolby Pro-Logic is the consumer version of theatrical Dolby stereo.

Dolby Pro Logic

Dolby Surround/Pro Logic is based on basic matrix technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into an ordinary stereo (two channel) sound track by using phase shift techniques. A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center, and a single limited frequency-range mono rear channel—while systems lacking the decoder play back the audio as standard Stereo.

Although Dolby Surround was introduced as an analog format, all Dolby Digital decoders incorporate a digitally implemented Dolby Surround Pro Logic decoder for digital stereo signals that carry matrix-encoded Dolby Surround.

Dolby Pro Logic II
In 2000, Dolby introduced Dolby Pro Logic II (DPL II), an improved implementation of Dolby Pro Logic. DPL II processes any high quality stereo signal source into "5.1"—five separate full frequency channels (left, center, right, left surround and right surround) plus one low-frequency-effects (deep bass) channel. Dolby Pro Logic II also decodes 5.1 channels from stereo signals encoded in traditional four-channel Dolby Surround. DPL II implements greatly enhanced steering compared to DPL, and as a result, offers an exceptionally stable sound field that simulates 5.1 channel surround sound to a much more accurate degree than the original Pro Logic.
Because of the limited nature of the original DPL, many consumer electronics manufactures introduced their own processing circuitry, such as the "Jazz", "Hall", and "Stadium" modes found on most common home audio receivers. DPL II forgoes this type of processing and replaces it with simple servo (negative feedback) circuits used to derive five channels. In addition to five full range playback channels, Pro Logic II introduced a Music mode which would not add any processing to the left and right channels, but will still extract a center channel and two surround channels, providing a net effect of a wider center channel.
The Pro Logic II system also features a mode designed specifically for video gaming, and it is frequently used in game titles for Sony's PlayStation 2, Nintendo's GameCube and Wii as an alternative to digital technologies like Dolby Digital, LPCM or DTS.

Dolby Pro Logic IIx

A newer Dolby Pro Logic IIx system is also now available, which can take stereo and Dolby Surround (sometimes called Dolby Stereo Surround) source material and up-convert it to 6.1, or 7.1 channel surround sound. Dolby Pro Logic IIx also takes signals intended for Dolby Pro Logic II, and up-converts them to a 6.1 or 7.1 channel surround sound.
Software encoding
The liba52 decoder library for AC3 and A52 digital sound optionally exports stereo sound compatible with Dolby Surround and Pro Logic.
The Handbrake software for Mac OS X is capable of downmixing Dolby Digital AC-3 5.1 to Stereo for Dolby Pro Logic I & II for surround playback

Pro Logic vs Dolby Surround
Dolby Surround is the encoding counterpart to Dolby Pro Logic's decoding technology, but early home implementations of Dolby Surround decoding went by the name Dolby Surround which can cause some confusion. Dolby Surround and Dolby Pro Logic decoders are similar in principle, as both use matrix technology to extract extra channels from stereo-encoded audio. However, Pro Logic uses advanced algorithms, superior to the earlier home Dolby Surround system and similar to the original cinema Dolby Stereo processors, in order to not only extract the extra channels, but to also improve steering and discreteness between the channels.

Digital cinema

Digital cinema refers to the use of digital technology to distribute and project motion pictures. The final movie can be distributed via hard drives [ex. Utilizing the CRU-Dataport DX115 removable disk drive carriers + DX115 carrier USB/SATA adapter], DVDs or satellite and projected using a digital projector instead of a conventional film projector. Digital cinema is distinct from high-definition television and in particular, is not dependent on using television or HDTV standards, aspect ratios, or frame rates. Digital projectors capable of 2K resolution began deploying in 2005, and since 2006, the pace has accelerated. HDTV and pre-recorded HD disks could put pressure on movie theaters to offer something to compete with the home HD experience.

In this article, 2K and 4K refer to images with 2048 and 4096 horizontal pixel resolution, respectively.

Technology

To match or improve the theater experience of movie audiences, a digital cinema system must provide high quality image, sound, subtitles, and captions. Theater managers require server controls for managing and displaying content in multiple theaters, and studios want their content encrypted with secure delivery, playback, and reporting of play times to the distribution company.

The Digital Cinema Initiatives (DCI), working in conjunction with members of the SMPTE standards committee, has published a system specification for digital cinema that was agreed upon by the major studios. Briefly, the specification calls for picture encoding using the ISO/IEC 15444-1 "JPEG2000" (.jp2) standard and use of the CIE XYZ color space at 12 bits per component encoded with a 2.6 gamma applied at projection, and audio using the "Broadcast Wave" (.wav) format at 24 bits and 48 kHz or 96 kHz sampling, controlled by an XML-format Composition Playlist, into an MXF-compliant file at a maximum data rate of 250 Mbit/s. Details about encryption, key management, and logging are all discussed in the specification as are the minimum specifications for the projectors employed including the color gamut, the contrast ratio and the brightness of the image.

Digital cinema conforming to the DCI Standard is referred to within the film industry as D-Cinema while all other forms of digital cinema are referred to as E-Cinema. Thus, while D-Cinema is a defined standard, though one that is still partly being framed by SMPTE as of 2007, E-Cinema may be anything, ranging from a DVD player connected to a consumer projector to something that approaches the quality of D-Cinema without conforming to some of the standards. Even D-Cinema itself has evolved over time before the DCI standards were framed. However, the current DCI standards were made with the intention of standing the test of time, much like 35 mm film which has evolved but still retained compatibility over a substantial part of a century.

Digital capture

As of 2007 the most common acquisition medium for digitally projected features is 35 mm film scanned and processed at 2K or 4K via digital intermediate. Most digital features to date have been shot at 1920x1080 HD resolution using cameras such as the Sony CineAlta, Panavision Genesis or Thomson Viper. New cameras such as the Arriflex D-20 and Silicon Imaging's SI-2K can capture 2K resolution images, and the Red Digital Cinema Camera Company's Red One can record 4k RAW. Thus the future of digital cinema can be expected to have as a standard 4K capture and 4K projection. Currently in development are other cameras capable of recording 4K RAW, such as Dalsa Corporation's Origin, and cameras capable of recording 5k RAW, such as the RED EPIC, and cameras capable of recording 3k RAW (for budget filmmakers) such as the RED SCARLET.

Digital post-production

Film is scanned from camera-original film negatives into a digital format on a scanner or high-resolution telecine. Data from digital motion picture cameras may be converted to a convenient image file format for work in a facility. All of the files are 'conformed' to match an edit list created by the film editor, and are then color corrected under the direction of the film's staff. The end result of post-production is a digital intermediate used to record the motion picture to film and/or for the digital cinema release.

Digital mastering

When all of the sound, picture, and data elements of a production have been completed, they may be assembled into a Digital Cinema Distribution Master (DCDM) which contains all of the digital material needed for a show. The images and sound are then compressed, encrypted, and packaged to form the Digital Cinema Package (DCP).

Digital cinema distributors

Technicolor, Deluxe Entertainment Services Group Inc., XDC and Access Integrated Technologies are the leading companies in digital distribution. Other companies currently distributing digital cinema include Kodak, DTS, Ascent Media, Dolby, Arts Alliance Media and Motion Picture Solutions.

Digital projection

There are currently two types of projectors for digital cinema. Early DLP projectors, which were deployed primarily in the U.S., used limited 1280×1024 resolution which are still widely used for pre-show advertising but not usually for feature presentations. The DCI specification for digital projectors calls for three levels of playback to be supported: 2K (2048×1080) at 24 frames per second, 4K (4096×2160) at 24 frames per second, and 2K at 48 frames per second.

Three manufacturers have licensed the TI-developed DLP Cinema technology. Christie Digital Systems, Barco and NEC. Christie is the maker of the CP2000 line of 2K DCI-compliant Digital Cinema Projectors, and long established in traditional film projector technology throughout the U.S. and is the market leader in terms of units sold and deployed internationally. NEC manufactures the Starus NC2500S, NC1500C and NC800C 2K projectors for large, medium and small screen respectively and the Starus Digital Cinema Server system, as well as other equipment to connect PCs, analog/digital tape decks and satellite receivers, DVD, and off-air broadcast, etc. for pre-show and special presentations. While NEC is a relative newcomer to Digital Cinema, Christie is the main player in the U.S. and Barco takes the lead in Europe and Asia.

The other soon-to-be-deployed-technology is from Sony and is labeled "SXRD" technology. Their projector provides 4096x2160 resolution.

Other manufacturers have been developing digital projector technology, but these have not yet been deployed into motion picture theaters and are not commercially available in versions that conform to the DCI specification.
As of July 2007, there are some cinemas in Singapore showing digital 4K films to public using Sony's CineAlta 4K digital projector. They are located at Golden Village Cinema in Vivocity (Hall 11), Eng Wah Cinema in Suntec (Hall 3), Shaw Cinema in Bugis (Hall 1 & 3) and at Cathay Cineplex (Hall 7).

In September 2007, Muvico Theaters Rosemont 18 in Rosemont, Illinois became the first theater in North America to have Sony's CineAlta 4K digital projectors for all 18 screens. Muvico Theaters intends on opening more theaters in the last quarter of 2008 and well into 2009 all utilizing Sony's CineAlta 4K digital projector.

Live broadcasting to movie theaters
Digital cinemas can deliver live broadcasts from performances or events. For example, there are regular live broadcasts to movie theaters of Metropolitan Opera performances.

Current developments

As of October 2007, there are over 5000 DLP-based Digital Cinema Systems installed.
By October 2007, DG2L Technologies was reported to have supplied 1500 Digital Cinema Systems to UFO Moviez Ltd. in India and Europe.

As of July, 2007, 1400 screens in the U.S. have been equipped with digital cinema projectors including a dozen theaters where the Sony 4K projector has been installed. In continental Europe, XDC is servicing over 300 screens in 10 countries, where Germany has the leading territory with over 100 installations.

The UK is home to Europe's first DCI compliant fully digital multiplex cinemas, Odeon Hatfield and Odeon Surrey Quays (London) have a total of 18 digital screens and were both launched on Friday 9 February 2007.

In June 2007, Arts Alliance Media announced the first European commercial digital cinema VPF agreements (with Twentieth Century Fox and Universal Pictures).

As of March 2007, with the release of Disney's Meet the Robinsons, about 600 screens have been equipped with 2K digital projectors that are equipped with Real D Cinema's stereoscopic 3D technology, marketed under the Disney Digital 3-D brand.

In mid 2006, about 400 theaters have been equipped with 2K digital projectors with the number increasing every month.

In February 2005, Arts Alliance Media was selected to roll out the UK Film Council’s Digital Screen Network (DSN), a $20M contract to install and operate Europe’s largest 2K digital cinema network. By March 2007, 230 of the 241 screens had been installed on schedule, with the remaining 11 to be installed later in 2007 when cinemas have completed building works or construction.

Chicken Little from Disney, with its experimental release of the film in digital 3D, increased the number of projectors using the 2K format. Several digital 3D films will surface in 2006 and several prominent filmmakers have committed to making their next productions in stereo 3D.

By early 2006, Access Integrated Technologies (AccessIT) had announced agreements with nearly all of the major film studios and several exhibitors that enable the company to roll-out its end-to-end digital cinema systems. In August 2006, the Malayalam digital movie Moonnamathoral was distributed via satellite to cinemas; thus becoming the first Malayalam digital film to be so distributed. This was done using the end-to-end digital cinema system developed by Singapore based DG2L Technologies.

On May 1, 2008, Public Radio International (PRI) spearheaded the first-ever digital cinema event in public media by working with Ira Glass and Chicago Public Radio on This American Life Live![5]. The event was presented exclusively in select theatres by National CineMedia's (NCM) Fathom, in partnership with BY Experience and Chicago Public Radio, and in association with Public Radio International.

Economics

Savings in distribution

Digital distribution of movies has the potential to save money for film distributors. A single film print can cost around US$1200[citation needed] (or $30,000 for a 1-time print of an 80-minute feature[7]), so making 4000 prints for a wide-release movie might cost $5 million. In contrast, at the maximum 250 megabit-per-second maximum data rate defined by DCI for digital cinema, a typical feature-length movie could fit comfortably on an off the shelf 300 GB hard drive—which cost as low as $70—which could even be returned to the distributor for reuse after a movie's run. With several hundred movies distributed every year, industry savings could potentially reach $1 billion or more.

Alternative content

An added incentive for exhibitors is the ability to show alternative content such as live special events, sports, pre-show advertising and other digital or video content. Some low-budget films that would normally not have a theatrical release because of distribution costs might be shown in smaller engagements than the typical large release studio pictures. The cost of duplicating a digital "print" is very low, so adding more theaters to a release has a small additional cost to the distributor. Movies that start with a small release could scale to a much larger release quickly if they were sufficiently successful, opening up the possibility that smaller movies could achieve box office success previously out of their reach.

Greater protection for content

A last incentive for digital distribution is the possibility of greater protection against piracy. With traditional film prints, distributors typically stagger the film's release in various markets, shipping the film prints around the globe. In the subsequent markets, pirated copies of a film (i.e. a cam) may be available before the movie is released in that market. A simultaneous worldwide release would mitigate this problem to some degree. Simultaneous worldwide releases on film have been used on The Da Vinci Code, Lord of the Rings: Return of the King, Star Wars: Revenge of the Sith, Charlie's Angels: Full Throttle and Mission: Impossible III amongst others. With digital distribution, a simultaneous worldwide release would not cost significantly more than a staggered release.

Costs

On the downside, the initial costs for converting theaters to digital are high: up to $150,000 per screen or more. Theaters have been reluctant to switch without a cost-sharing arrangement with film distributors. Recent negotiations have involved the development of a Virtual Print License fee which the studios will pay for their products which allows financiers and system developers to pay for deployment of digital systems to the theaters, thus providing investors a certain payback.

While a theater can purchase a film projector for US$50,000 and expect an average life of 30–40 years, a digital cinema playback system including server/media block/and projector can cost 3–4 times as much, and is at higher risk for component failures and technological obsolescence. Experience with computer-based media systems show that average economic lifetimes are only on the order of 5 years with some units lasting until about 10 years before they are replaced.

Archiving digital material is also turning out to be both tricky and costly. In a 2007 study, the Academy of Motion Picture Arts and Sciences found the cost of storing 4K digital masters to be "enormously higher - 1100% higher - than the cost of storing film masters." Furthermore, digital archiving faces challenges due to the insufficient temporal qualities of today's digital storage: no current media, be it optical discs, magnetic hard drives or digital tape, can reliably store a film for a hundred years, something that properly stored and handled film can do.[8]

History

Digital media playback of hi-resolution 2K files has at least a twenty year history with early RAIDs feeding custom frame buffer systems with large memories. Content was usually restricted to several minutes of material.
Transfer of content between remote locations was slow and had limited capacity. It wasn't until the late 1990s that feature length projects could be sent over the 'wire' (Internet or dedicated fiber links).

There were many prototype systems developed that claim a first in some form of digital presentation. However, few of these had a significant impact on the advance of the industry. Key highlights in the development of digital cinema would likely include: demonstrations by TI of their DMD technology, real-time playback of compressed hi-resolution files by various vendors, and early HD presentations from D5 tape to digital projectors.

Standards development

The Society of Motion Picture and Television Engineers began work on standards for digital cinema in 2001. It was clear by that point in time that HDTV did not provide a sufficient technological basis for the foundation of digital cinema playback. (In Europe and Japan however, there is still a significant presence of HDTV for theatrical presentations. Agreements within the ISO standards body have led to these systems being referred to as Electronic Cinema Systems (E-Cinema)).

Digital Cinema Initiatives (DCI) was formed in March 2002 as a joint project of the motion picture studios (Disney, Fox, MGM, Paramount, Sony Pictures Entertainment, Universal and Warner Bros. Studios) to develop a system specification for digital cinema. In cooperation with the American Society of Cinematographers, DCI created standard evaluation material (the ASC/DCI StEM material) and developed tests of 2K and 4K playback and compression technologies. DCI published their specification in 2005.

Claims to significant events

One claim for the first digital cinema demonstration comes from JVC. On March 19, 1998, they collaborated on a digital presentation at a cinema in London. Several clips from popular films were encoded onto a remote server, and sent via fibre optic for display to a collection of interested Industry parties.

The Last Broadcast made cinematic history on October 23, 1998, when it became the first feature to be theatrically released digitally, via satellite download to theaters across the United States. An effort headed by Wavelength Releasing, Texas Instruments, Digital Projection Inc. and Loral Space, it successfully demonstrated what would become a template for future releases. In 1999, it was repeated utilizing QuVIS technology across Europe, including the Cannes Film Festival, making The Last Broadcast the first feature to be screened digitally at the Cannes Film Festival.

Several feature films were shown in 1999 using DLP prototype projectors and early wavelet based servers. For example, Walt Disney Pictures Bicentennial Man was presented using a Qubit server manufactured by QuVIS of Topeka, Kansas. DVD ROM was used to store the compressed data file. The DVD ROMs were loaded into the QuBit server hard drives for playout. The file size for Bicentennial Man was 42 GB with an average data rate of 43 Mbit/s.
In 2000, Walt Disney, Texas Instruments and Technicolor with the cooperation of several U.S. and international exhibitors, began to deploy prototype Digital Cinema systems in commercial theatres. The systems were assembled and installed by Technicolor using the TI mark V prototype projector, a special Christie lamp housing, and the QuBit server with custom designed automation interfaces.

Technicolor manufactured the DVDs for uploading on these test systems and was responsible for sending technicians out to the locations for every new feature film that was played. The technicians would typically spend ten or so hours to load the files from the DVD to the QuBit, set up the server to play the files, and then set up the projector. A full rehearsal screening of the feature was mandatory as was the requirement to have back up DVDs and backup QuBits available should something fail.

The systems were eventually replaced or upgraded after TI made improvements to the projectors and Technicolor developed a purpose-built digital cinema server in a venture with Qualcomm, the engineering giant from San Diego best known for advanced mobile phone technology. The new systems were called AMS for Auditorium Management Systems and were the first digital cinema servers designed to be user friendly and operate reliably in a computer-hostile environment such as a projection booth. Most importantly, they provided a complete solution for content security.

The AMS used removable hard disk drives as the transport mechanism for the files. This eliminated the time required to upload the DVD ROMs to the local hard drives and provided the ability to switch programs quickly. For security, the AMS used a media block type system that placed a sealed electronics package within the projector housing. The server output only 3DES encrypted data and the media block did the decryption at the point just before playout.

The first secure encrypted digital cinema feature was Star Wars Episode II: Attack of the Clones. The system functioned well but was eventually replaced because of the need to create a standard data package for D-cinema distribution.

Universal Pictures used their film Serenity as the first DCI-compliant DCP to be delivered shown to an audience at a remote theater, although it was not distributed this way to the public. Inside Man was their first DCP cinema release, and was transmitted to 20 theatres in the United States along with two trailers.

In April 2005, DG2L Technologies announced that it had been awarded the multi-million dollar contract for the world's largest satellite based MPEG4 digital cinema deployment to be done in India, which encompassed 2000 theaters for UFO (United Film Organizers), a subsidiary of the Valuable Media Group. In Mar 2006, United Film Organizers Moviez (UFO Moviez), had reached a significant milestone—surpassing 30,000 shows using the DG2L Cinema System platform. This figure increased to 100,000 shows in August 2006. In September 2006, UFO Moviez acquired 51% stake in DG2L Technologies in a deal estimated at around $50 million.

Stereo 3-D images
In late 2005, interest in digital 3-D stereoscopic projection has led to a new willingness on the part of theaters to co-operate in installing a limited number of 2K stereo installations to show Disney's Chicken Little in 3-D film. Seven more digital 3-D movies are slated for 2006 or 2007 release (including Beowulf, Monster House and Meet the Robinsons). The technology combines digital projectors with the use of polarized glasses and screens. DLP technology is well-suited for stereo 3-D as it can handle the higher frame rates required for flicker free presentations.

Digital Theater System

DTS (also known as Digital Theater Systems), owned by DTS, Inc. (NASDAQ: DTSI), is a multi-channel digital surround sound format used for both commercial/theatrical and consumer grade applications. It is used for in-movie sound both on film and on DVD, and during the last few years of the Laserdisc format's existence, several releases had DTS soundtracks.

History

One of the company's initial investors was film director Steven Spielberg, who felt that theatrical sound formats up until the company's founding were no longer state of the art, and as a result were no longer optimal for use on projects where quality sound reproduction was of the utmost importance. Work on the format started in 1991, four years after Dolby Labs started work on its new codec, Dolby Digital. The basic and most common version of the format is a 5.1 channel system, similar to a Dolby Digital setup, which encodes the audio as five primary (full-range) channels plus a special LFE (low-frequency effect) channel, for the subwoofer.

Note however that encoders and decoders support numerous channel combinations and stereo, four-channel and four-channel+LFE soundtracks have been released commercially on DVD, CD and Laserdisc.

Other newer DTS variants are also currently available, including versions that support up to seven primary audio channels plus one LFE channel (DTS-ES). DTS's main competitors in multichannel theatrical audio are Dolby Digital and SDDS, although only Dolby Digital and DTS are used on DVDs and implemented in home theater hardware. Spielberg debuted the format with his 1993 production of Jurassic Park, which came slightly less than a full year after the official theatrical debut of Dolby Digital (Batman Returns). In addition, Jurassic Park also became the first home video release to contain DTS sound when it was released on LaserDisc in January 1997, two years after the first Dolby Digital home video release (Clear and Present Danger on Laserdisc) which debuted in January of 1995.

In theatrical use, information in the form of a modified time code is optically imaged onto the film. An optical LED reader reads the timecode data off the film and sends it to the DTS processor which uses this timecode to synchronize the projected image with the soundtrack audio. The actual audio is recorded in compressed form on standard CD-ROM media at a bitrate of 1,103 kbit/s. The processor also acts as a transport mechanism, as it holds and reads the audio discs. Newer units can generally hold three discs, allowing a single processor/transport to handle two-disc film soundtracks along with a third disc containing sound for theatrical trailers. In addition, specific elements of the imprinted timecode allow identifying data to be embedded within the code, ensuring that a certain film's soundtrack will only run with that film. DTS provided the Digital Audio for IMAX until 2001, when Dolby took over.

DTS and Dolby Digital (AC-3), DTS's chief competitor in the cinema and home theater market, are often compared due to their similarity in product goals. In theatrical installations, AC-3 audio is placed between sprocket holes, leaving the audio content susceptible to physical damage due to film wear and mishandling. DTS audio is stored on a separate set of CD-ROM media, whose greater storage capacity affords the potential to deliver better audio fidelity. However, the separation of print film and audiotrack is both a blessing and a curse. AC-3 (and SDDS) reside entirely on the 35 mm film itself, simplifying distribution by eliminating an extra (optional) deliverable. But DTS's CD-ROM media is not subject to the usual wear and damage suffered by the film print during the normal course of the movie's theatrical screening. Disregarding the separate CD-ROM assembly as a potential point of failure, the DTS audiopath is comparatively impervious to film degradation, excepting that the film-printed timecode is completely destroyed.

In the consumer (home theater) market, AC-3 and DTS are close in terms of audio performance. When the DTS audio track is encoded at its highest legal bitrate (1,536 kbit/s), technical experts rank DTS as perceptually transparent for most audio program material (i.e., indistinguishable to the uncoded source in a double blind test.) Dolby claims its competing AC-3 codec achieves similar transparency at its highest coded bitrate (640 kbit/s). However, in program material available to home consumers (DVD, broadcast and subscription Digital TV), neither AC-3 nor DTS run at its highest allowed bitrate. DVD and broadcast (ATSC) HDTV cap AC-3 bitrate at 448 kbit/s. But even at 448 kbit/s, consumer audio gear already enjoys better audio performance than theatrical (35 mm movie) installations, which are limited to even lower bitrates. When DTS-audio was introduced to the DVD specification, studios authored DVD-movies at DTS's full bitrate (1,536 kbit/s). Later movie titles were almost always encoded at a reduced bitrate of 768 kbit/s, ostensibly to increase the number of audio-tracks on the movie disc. At this reduced rate (768 kbit/s), DTS no longer retains audio transparency.

AC-3 and DTS are sometimes judged by their encoded bitrates. DTS proponents claim that the extra bits give higher fidelity and more dynamic range, providing a richer and more lifelike sound. But no conclusion can be drawn from their respective bitrates, as each codec relies on different coding tools and syntax to compress audio. When the DTS and AC-3 audiotracks on the same DVD are compared, some movies exhibit noticeable differences. A DTS track is often louder with less hiss, even at the same relative playback volume.

DTS as a codec

DTS is an enhanced copy of a French patent called LC Concept, first used in 1990 for the movie Cyrano de Bergerac which received the best sound award at the César Awards in 1991.

On the consumer level, DTS is the oft-used shorthand for the DTS Coherent Acoustics codec, transportable through S/PDIF and used on DVDs, CDDAs, LDs and in wave files. This system is the consumer version of the DTS standard, using a similar codec without needing separate DTS CD-ROM media.

There are significant technical differences between commercial/theatrical and home variants: the former being a traditional ADPCM compression system and the latter a sophisticated hybrid perceptual and signal-redundancy compressor based on ADPCM called APTX-100.

DTS playback

Both music and movie DVDs allow delivery of DTS audio tracks. But DTS was not part of the original DVD specification (1997), so early DVD players did not recognize DTS audio tracks at all. The DVD specification was revised to allow optional inclusion of DTS audio tracks. The DVD title must carry one or more primary audio tracks in AC-3 or LPCM format (in Europe, MPEG-1 is also an allowed primary track format). The DTS audio track, if present, can be selected by the user. Modern DVD players can now decode DTS natively with no problem, or pass it through to an external decoder. Nearly all standalone receivers and many integrated ("home theater in a box") DVD player/receivers manufactured today can decode DTS.

For PC playback, many software players support the decoding of DTS. The VideoLAN project has created a decoding module for DTS called libdca (formerly libdts), which is the first open source implementation of DTS. The Sony Playstation 3 and Xbox 360 are capable of DTS decoding and output via Toslink or HDMI as LPCM. However on the 360, this feature is only found on new the Elite model and newer models available since. Only the Playstation 3 console has the ability to decode DTS-HD Master Audio or High Resolution since the newest firmware update, ver. 2.30 and up. The Xbox 360 can only output the core bitstream at 1.5 Mbit/s via LPCM or Toslink.

DTS variants

In addition to the standard 5.1 channel DTS Surround codec, the company has several other technologies in its product range designed to compete with similar systems from Dolby Labs. The primary new technologies are:

DTS 70 mm

This is a process designed specifically for playback in motion picture theaters equipped with 70mm projection and 6-track stereophonic surround sound. It is believed that this is the digital equivalent of the 70mm Dolby Stereo 6-Track analog mixing process. It works the same way that 35 mm DTS does, only the size of the print stock is bigger. The 6-track audio data is played on special compact discs in synchronization with the picture that is projected on a screen. The 6-track system plays on a properly organized 5.1 system: left, right, center, LFE speaker, and split surrounds.

DTS-ES

DTS-ES (DTS Extended Surround) includes two variants, DTS-ES Matrix and DTS-ES Discrete 6.1, depending on how the sound was originally mastered and stored. DTS-ES Discrete provides 6.1 discrete channels, with a discretely recorded (non-matrixed) center-surround channel; in home theater systems with a 7.1 configuration, the two rear-center speakers play in mono. DTS-ES Matrix provides 5.1 discrete channels with a matrixed center-surround audio channel. DTS-ES commonly works on a matrix system, whereby processors that are compatible with the ES codec look for and recognize "flags" built into the audio coding and "un-fold" the rear-center sound from data that would otherwise be sent to rear surround speakers.

This is notated as DTS-ES 5.1. Less frequently, DTS-ES data can be encoded with a discrete sixth audio channel (the rear-center), meaning that the audio data for the sixth channel is stored separately from the other information, and is not embedded or matrixed among other channels. This is notated as DTS-ES 6.1, as the center rear is completely discrete from the other channels. ES capable processors can recognize the discrete sixth channel, and play it back if connected to the necessary speaker(s). In contrast, Dolby's competing EX codec, which also boasts a center rear channel, can only handle matrixed data and does not support a discrete sixth channel. DTS-ES is backward compatible with standard DTS setups, so non-ES equipment which does not recognize the flags or with ES enabled equipment that lack the extra speaker connections, sound plays back in 5.1 as if it were standard DTS. Only a few DVD titles have been released with DTS-ES Discrete.

DTS NEO:6

DTS NEO:6, like Dolby's Pro Logic IIx system, can take stereo content and convert the sound into 5.1 or 6.1 channel format.

DTS 96/24

DTS 96/24 allows the delivery of 5.1 channels of 24-bit, 96 kHz audio and high quality video on the DVD-Video format. Prior to the invention of DTS 96/24, it was only possible to deliver two channels of 24-bit, 96 kHz audio on DVD-Video. DTS 96/24 can also be placed in the video zone on DVD-Audio discs, making these discs playable on all DTS compatible DVD players.

DTS-HD High Resolution Audio

DTS-HD High Resolution Audio, like DTS-HD Master Audio, is an extension to the original DTS audio format. It delivers up to 7.1 channels of sound at 96 kHz sampling frequency and 24 bit depth resolution. DTS-HD High Resolution Audio is selected as an optional surround sound format for Blu-ray Disc and HD DVD with constant bit rates up to respectively 6.0 Mbit/s and 3.0 Mbit/s. It is supposed to be an alternative for DTS-HD Master Audio where disc space may not allow it.

DTS-HD Master Audio

DTS-HD Master Audio, previously known as DTS++ and DTS-HD, supports a virtually unlimited number of surround sound channels, can downmix to 5.1 and two-channel, and can deliver audio quality at bit rates extending from DTS Digital Surround up to lossless (24-bit, 192 kHz). DTS-HD Master Audio is selected as an optional surround sound format for Blu-ray and HD DVD, where it has been limited to a maximum of 8 discrete channels. DTS-HD MA supports variable bit rates up to 24.5 Mbit/s on a Blu-ray Disc and up to 18.0 Mbit/s for HD-DVD, with 6 channel encoded at up to 192 kHz or 8 channels encoded at 96 kHz/24 bit. In case more than 6 channels are used, a "Channel Remapping" function allows for remixing the soundtrack to compensate for a different channel layout in the playback system compared to the original mix. Currently the Japanese version Pioneer BDP-LX80 supports bitstream digital output of the format along with the Samsung BD-P1400 (through a firmware update). All Blu-ray and HD DVD players can decode the DTS "core" resolution soundtrack at 1.5 Mbit/s, however. DTS-HD Master Audio and Dolby TrueHD are the only technologies that deliver compressed lossless surround sound for these new disc formats, ensuring the highest quality audio performance available in the new standards. (N.B.: DTS Coherent Acoustics coding system has been selected as mandatory audio technology for both the Blu-ray Disc (BD) and High Definition Digital Versatile Disc (HD DVD).

Others

- DTS Connect: This is a real-time encoding technology for interactive media available on the computer platform only. It converts any audio signals on a PC into the 5.1-channel DTS format and transports it via a single S/PDIF cable. It is found on soundcards with CMedia CMI8788/CMI8770 Soundcontroller and onboard audio with Realtek ALC883DTS/ALC889A/ALC888DD-GR and SoundMAX AD1988 chip.

- DTS Interactive: This is a realtime DTS stream encoder. It is a part of DTS Connect, and can be found on stand alone devices (e.g., Surround Encoder, HD DVD / Blu-ray Player). Nearly a dozen titles on the PlayStation 2 feature the "DTS Interactive" realtime stream encoder, such as Grand Theft Auto: Vice City, and Terminator 3: Rise of the Machines.

- DTS Surround Sensation: A relatively new development, previously known as DTS Virtual. It allows a virtual 5.1 surround sound to be heard through a standard pair of headphones.