Dolby Digital

Dolby Digital ( ATSC A/52 and also AC-3) is a multi -channel sound system of Dolby, the technology in the film (cinema), comes to laser discs, DVDs, Blu-rays and in television technology used. In the field of cinema and DVD direct competitors DTS and SDDS are (SDDS only cinema). Dolby Digital support up to six discrete channels and uses a psychoacoustic lossy data compression method.

The format has been standardized internationally by the Advanced Television Systems Committee to the document number A/52 and thus contributes officially named the ATSC A/52. Dolby Digital is the marketing name ( often abbreviated to DD). AC - 3, finally, refers to the bitstream format ( Adaptive Transform Coder 3) and has also been naturalized as a label. This is also where the typical file extension. Ac3.

Also slightly different names such as Dolby Digital or Dolby Stereo SR- Digital and some others can be used.

  • 3.1 Cinema
  • 3.2 home users 3.2.1 Dolby Digital Live

History

The first official movie in Dolby Digital was Batman Returns 1992 There were already in the U.S. a few test copies in Dolby Digital. (Including Star Trek VI: The Undiscovered Country ).

1995 Dolby Digital was established as a possible audio format for DVD. Moreover, the first laser disc was released with this audio format.

The first commercially available in Germany receivers for the home, the Dolby Digital Compatible, was the come on the market in May 1996, Kenwood KR- V990D.

Technical details

Channels

Dolby Digital contains up to six channels. Specifically, these are:

  • Front left and right,
  • Front center (center),
  • Rear left and right ( surround channels ),
  • LFE (Low Frequency Effects, subwoofer).

Channel following configurations are possible:

  • Dolby Digital 1 /0 - mono; Channels: Center - Especially old restored films
  • Dolby Digital 1/0.1 - mono LFE; Channels: Center, Subwoofer
  • Dolby Digital 2 /0 - stereo; Channels: Front Left, Front Right - For example, audio commentary. Can also contain Dolby Surround information.
  • Dolby Digital 2/0.1 - Stereo with LFE; Channels: Front Left, Front Right, Subwoofer
  • Dolby Digital 3 /0 - 3 stereo; Channels: front left, front right, center
  • Dolby Digital 3/0.1 - 3 Stereo with LFE; Channels: Front Left, Front Right, Center; subwoofer
  • Dolby Digital 2 /1 - stereo with mono surround; Channels: Front Left, Front Right, Surround ( mostly distributed on SUR left and right)
  • Dolby Digital 2/1.1 - stereo with mono surround and LFE; Channels: Front Left, Front Right, Surround (on SUR L R), Subwoofer
  • Dolby Digital 3 /1 - 3 stereo with mono surround; Channels: Front Left, Front Right, Center, Surround ( on SUR L R)
  • Dolby Digital 3/1.1 - 3 stereo with mono surround and LFE; Channels: Front Left, Front Right, Center, Surround ( on SUR L R), Subwoofer
  • Dolby Digital 2 /2 - quadraphonic; Channels: Front left, front right, surround left, surround right
  • Dolby Digital 2/2.1 - quadraphonic with LFE; Channels: Front left, front right, surround left, surround right, subwoofer
  • Dolby Digital 3 /2 - 5 - channel surround; Channels: Front left, front right, center, surround left, surround right
  • Dolby Digital 3/2.1 - 5 - channel surround LFE; Channels: Front left, front right, center, surround left, surround right, subwoofer - Mostly used as main audio with movies or series.

The full channel equipment is referred to as 5.1 audio, as only the first five channels play the entire possible frequency range of 20 Hz to 20 kHz. The LFE channel is limited to between 20 and 120 Hz Tieftoneffekte.

Dolby Digital works with discrete channels, ie all channels are completely independent and in principle. In contrast, such as Dolby Pro Logic, which encrypts four channels in a stereo signal by matrix encoding.

Audio compression

The audio signal is not compressed in its dynamics. Due to the large number of channels, the high sampling rate of 48 kHz and the possible resolution 16-24 bit falls in uncompressed form of a massive amount of audio data. For the audio track of a two-hour film, the space required is about 4 GB, which corresponds to about half capacity of a double-layer DVD. Therefore Dolby Digital uses a lossy data compression. The encoding method used is called AC-3 and is described in the ATSC A/52. The compression is based - for example, even with MP3, Vorbis and AAC - on the fact that the human ear does not perceive certain sound information (see psychoacoustics ).

AC-3 supports bit rates 32-640 kbit / s ( kilobits per second). Usually 384 or 448 kbit / s on a DVD for 5.1 sound used for stereo 192 or 224 kbit / s In the cinema, the data rate is 320 kbit / s

Signaling

For data signaling RS -422 will be used.

Use of Dolby Digital

Cinema

For sound films in the cinema Dolby Digital is ( in the industry referred to as SRD) the successor of the analog optical sound Dolby Stereo SR. The data is also stored for Dolby Stereo SR- optical sound track between the holes of the film perforation and read using a special CCD camera. The available there place is so small that the Dolby logo is seen in the middle of the data block only with a magnifying glass. If Dolby Digital from, the sound system will automatically switch back without interruption to the Dolby Stereo SR- optical sound.

Dolby Digital can be retrofitted on all standard 35mm projectors.

Digital cinema according to the standard of the Digital Cinema Initiatives provides for the tone only uncompressed PCM, so that classical cinema sound systems such as Dolby Digital or DTS are no longer needed there.

Home users

In the home Dolby Digital is the digital successor to Dolby Surround or Dolby Pro Logic. These metadata are contained in the audio track ( referred to as a BSI bit stream information ), which have two important functions, inter alia.

  • Dynamic Range Control. To a compatible decoder, it is possible to change the dynamics of the audio playback during playback automatically so that a uniform sound level arises. These quiet passages of the soundtrack are lifted and lowered loud. Sometimes this function is also called Midnight Mode ( midnight mode).
  • Stereo downmix. For users who do not have a 5.1 speaker system, 6 - channel audio in unaltered form unusable. AC -3 offers in the BSI information to the decoder as a guide to converting 5.1 to stereo. This opens up the possibility to deliver DVDs exclusively with 6- channel sound and to waive an additional stereo audio track.

Dolby Digital Live

Dolby Digital Live (DDL ) is a Encodierungs technique in real time for interactive media such as video and computer games. DDL converts any audio signal in the computer or the game console into a 5.1 - channel Dolby Digital format and can be output this signal via the S / PDIF output. The SoundStorm chip, which was used in the Xbox and some nForce2 - computer motherboards, used an early form of this technology. DDL is currently of sound cards made by Creative, Turtle Beach, HT OMEGA SYSTEM and Auzentech through the C-Media chipset used, and on some motherboards Realtek ALC882D, ALC888DD and ALC888H used. A similar technique is available under DTS Connect, DTS competitors. The open- source project AC3Filter also converts into real-time audio signals in the computer in Dolby Digital, so that they can be output via S / PDIF. However, this is not licensed from Dolby ..

An important advantage of this technique is that it allows the use of digital multichannel sound with sound cards that would otherwise limited to PCM stereo or multichannel analog audio.

DDL is to be found among the components for the newer label " Dolby Home Theater". Devices with this label knowledge of the following technologies: Dolby Pro Logic IIx, Dolby Headphone, Sound Space Expander, Natural Bass and Dolby Digital Live simply.

TV studios

Dolby Digital is used primarily in the consumer sector. In television studios, the Dolby Digital signal is obtained immediately before the release via transcoding from the Dolby E studio used internally as part of the production processing. Unlike Dolby E Dolby Digital has no exact time alignment to the video signal, which is essential in video switchers.

Extensions

Dolby Digital EX

Instead of the two rear channels Dolby Digital EX three ( rear right, rear center, rear left). This method is backward compatible, as the three rear channels are not stored separately but the central channel is formed from the left and right. It therefore has similarity to the analog Dolby Surround Pro Logic II

Dolby Digital Plus

Dolby Digital Plus was developed specifically for use with HDTV and HD DVDs or Blu- ray discs. The codec E -AC -3 to data rates up to 6 Mbit / s ( DVD: 448 kbit / s) support for up to 14 channels at 24 -bit resolution and a sampling frequency of 96 kHz.

Dolby Digital on TV / radio

  • Prerequisite for the use of Dolby Digital is the digital TV or radio reception via DVB or DAB.
  • April 26, 2001: After ProSieben also decided the pay-TV provider Premiere to broadcast Dolby Digital. The first film to premiere was on 26 April 2001, "Star Wars Episode I: The Phantom Menace ".
  • On September 17, 2003, Sat.1 began with the first Dolby Digital tests. Again, movies are broadcast in this format on a regular basis. Sat.1 also already showed football matches in Dolby Digital 5.1.
  • On 4 October 2003 Dolby Digital launched finally in the public service broadcasters. The ZDF broadcast "Wetten, dass. " The show in Dolby Digital 5.1 from.
  • From the 31 October 2003, the Bayerischer Rundfunk transfers " Bayern 4 Klassik " ​​in the fortnightly cycle Classical music from 2.05 bis 4 clock in Dolby Digital 5.1
  • September 3, 2004: The ORF started on 3 September 2004, a Dolby Digital 5.1 radio test program. The first broadcast on the test channel was broadcast on the occasion of the "Long Night of Radio Art " of the radio program OE1. The broadcast was transmitted from 19:30 bis 06:00 clock clock in Dolby Digital 5.1 on 3 September 2004. On this shaft are subsequently often classical concerts - shows live from the Great Hall of the Musikverein in Vienna - broadcast in Dolby Digital 5.1.
  • On 7 August 2005, the concert series of the 36th International Burghausen Jazz Week began. BR -alpha has sent the first channel of the ARD Group for all the concerts of the festival in the sound format Dolby Digital 5.1.
  • On 3 September 2005, the first also sent 3sat in the course of transmission of the Salzburg Festival in Sound format Dolby Digital 5.1.
  • Since 2005, the Bayerischer Rundfunk transfers " Bayern 4 Klassik " ​​regular live concerts from the Hercules Hall and the Gasteig in Munich in Dolby digital 5.1, since 2006, the performances of the Bayreuth Festival. The other classic radio programs of ARD follow. WDR3 To transfer, hr2, SWR 2, MDR Figaro, NDR Kultur since also frequent concerts in Dolby Digital 5.1. Moreover, these stations transmit the normal stereo program in Dolby Digital 2.0, so that the dynamics of the music as opposed to the FM radio and the normal TV sound (mpeg ) is not compressed, so you often transmits the full dynamics of the music here.
  • On 12 December 2005, the ZDF broadcast first time a movie ( " The Time Machine ") in the Sound format Dolby Digital 5.1. ZDF for several years already transmitting in Dolby Digital, but mainly in stereo. "Wetten, dass. " Few programs have been broadcast in DD 5.1. Furthermore, was given the opening of the Allianz Arena by ZDF in Dolby Digital 5.1.
  • March 20, 2006: RTL Television will start broadcasting via satellite with an additional Dolby Digital soundtrack. The first shipment 5.1 is the movie " Lord of the Rings - The Two Towers " on 16 April 2006.
  • May 7, 2006: RTL transfers during the European Grand Prix on the Nürburgring for the first time a Formula 1 race in Dolby Digital 5.1 method.
  • June / July 2006: ARD, ZDF and RTL will broadcast the games of the Football World Cup 2006 in Dolby Digital 5.1.
  • April 2007: MDR Sputnik begins on the radio series " Sputnik Studio Concerts " in 5.1 live to send. Every month, current chart bands in the studio playing in front of guests and transmitted simultaneously. Have played until now the Arctic Circle 18, client, Dena Joy Lane and Wir sind Helden.
  • The HDTV offshoot of the private and the public television constantly lead a Dolby Digital stream with itself (either stereo or 5.1). These are also those programs that send only a MP2 stream in SD format.
Dolby Laboratories Technology of television Kenwood Corporation Low-frequency effects 5.1 surround sound RS-422 Sound-on-film Downmixing DTS (sound system) Crossover switch Dolby Digital#Dolby Digital EX Fictional film Sputnik (radio station) Client (Band) Deluxe Music
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