Dolby Digital

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Current Dolby Digital logo (2014)

Dolby Digital (also ATSC A / 52 and AC-3 ) is a multichannel sound system of the Dolby company , which is now freely available due to the expiry of the patents , which is used in film technology ( cinema ), on laser discs , DVDs , Blu-ray discs and in television technology is used. The last relevant patent for Dolby Digital expired in March 2017. In the cinema and DVD sector, the direct competitors are DTS and SDDS (SDDS only cinema). Dolby Digital supports up to six discrete channels and uses a psychoacoustic lossy method for data compression.

The format was standardized internationally by the Advanced Television Systems Committee with document number A / 52 and is thus officially called ATSC A / 52 . Dolby Digital is the marketing name (often shortened to DD ). Finally, AC-3 denotes the bitstream format ( Adaptive Transform Coder 3 ) and has also become a common name, hence the typical file extension .ac3 .

Slightly modified terms such as Dolby Stereo Digital , Dolby SR-Digital or the simple abbreviation SRD and a few others are also used.

Logo in 2011
Old Dolby Digital logo


Schematic representation of Dolby Digital 5.1

The first official movie in Dolby Digital was Batman's return in 1992. But there were already some test copies in Dolby Digital in the USA (including Star Trek VI: The Undiscovered Land ).

In 1995, Dolby Digital was established as one of the possible audio formats for DVD . The first laser disc with this sound format also appeared .

The first receiver available in Germany for the home sector that supported Dolby Digital was the Kenwood KR-V990D , which was launched in May 1996 .

Technical details


Possible channel configurations with Dolby Digital
Surname mode Front Back Subwoofer
( LFE )
Left Middle
Right Surround
Dolby Digital 1/0 Mono No Yes No No No No Especially old restored films.
Dolby Digital 2/0 stereo Yes No Yes No No No Audio commentary. May also contain Dolby Surround information.
Dolby Digital 3/0 3 stereo Yes Yes Yes No No No
Dolby Digital 2/1 Stereo with mono surround Yes No Yes Yes No
Dolby Digital 2 / 1.1 Stereo with mono surround and LFE Yes No Yes Yes Yes
Dolby Digital 3/1 3 stereo with mono surround Yes Yes Yes Yes No
Dolby Digital 3 / 1.1 3 stereo with mono surround and LFE Yes Yes Yes Yes Yes
Dolby Digital 2/2 Quadrophony Yes No Yes Yes Yes No
Dolby Digital 2 / 2.1 Quadrophony with LFE Yes No Yes Yes Yes Yes
Dolby Digital 3/2 5-channel surround Yes Yes Yes Yes Yes No
Dolby Digital 3 / 2.1 5-channel surround with LFE Yes Yes Yes Yes Yes Yes Mostly used as the main soundtrack in feature films or series.

The full channel configuration is referred to as 5.1 tone, since only the first five channels reproduce the complete possible frequency spectrum from 20 Hz to 20 kHz. The LFE channel is limited to bass effects between 20 and 120 Hz.

Dolby Digital works with discrete channels; H. all channels are completely and in principle independent. In contrast, z. B. Dolby Pro Logic , which encodes four channels in a stereo signal using matrix coding.

Audio compression

The dynamic of the audio signal is not compressed. Due to the large number of channels, the high sampling rate of 48 kHz and the possible resolution between 16 and 24 bits, an enormous amount of audio data is generated in uncompressed form. For the soundtrack of a two-hour film, the space requirement is around 4 GB, which is roughly half the storage capacity of a double-layer DVD . That is why Dolby Digital works with lossy data compression . The coding method used is called AC-3 and is described in the ATSC A / 52 standard. As with MP3 , Vorbis and AAC , for example, the compression is based on the fact that the human ear does not perceive certain sound information ( see psychoacoustics ).

AC-3 supports bit rates between 32 and 640 kbit / s (kilobits per second). On a DVD , 384 or 448 kbit / s is usually used for 5.1 sound, and 192 or 224 kbit / s for stereo sound. In the cinema, the data rate (when using Dolby Digital) was 320 kbit / s (uncompressed PCM is now used). On a Blu-ray, 640 kbit / s are usually used for 5.1 sound, which means that the highest possible bit rate is used to the full.

Use of Dolby Digital

movie theater

Dolby Digital with other audio formats on 35mm film

For sound films in the cinema, Dolby Digital (referred to in the industry as SRD ) is the successor to the analog light sound Dolby Stereo SR . In addition to the Dolby Stereo SR soundtrack, the data is stored between the holes in the film perforation and read out using a special CCD camera . The space available there is so small that the Dolby logo in the middle of the data block can only be seen with a magnifying glass. If Dolby Digital fails , the sound system automatically switches back to the Dolby Stereo SR light tone without interruption .

Dolby Digital can be retrofitted to all common 35 mm projectors.

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

Home users

In the home environment, Dolby Digital is the digital successor to Dolby Surround or Dolby Pro Logic . The metadata contained in the audio track (referred to as BSI for Bit Stream Information ), which among other things offer two important functions, should be emphasized .

Variants of AC-3 decoding
  • Dynamic Range Control . With a compatible decoder, it is possible to automatically change the dynamics of the sound playback during playback so that a uniform volume level is created. For this purpose, quiet passages of the sound track are raised and loud passages are lowered. Sometimes this function is also called Midnight Mode .
  • Stereo downmix . For users who do not have a 5.1 speaker system, the unchanged 6-channel sound cannot be used. In the BSI information, AC-3 provides the decoder with assistance in converting from 5.1 to stereo. This opens up the possibility of delivering DVDs with only 6-channel sound and of doing without an additional stereo sound track.

Dolby Digital Live

Dolby Digital Live (DDL) is a real-time encoding technology for interactive media such as video and computer games. DDL converts any audio signal in the computer or game console into a 5.1-channel Dolby Digital format and can output this signal via the S / PDIF output. The SoundStorm chip used on the Xbox and some nForce2 computer motherboards used an early form of this technology. DDL is currently used by Creative, Turtle Beach , HT OMEGA SYSTEM and Auzentech sound cards through the C-Media chipset, and Realtek's ALC882D, ALC888DD and ALC888H are used on some motherboards . A similar technique is available under DTS Connect from competitor DTS . The open source project AC3Filter also converts audio signals in the computer into Dolby Digital in real time, so that they can be output via S / PDIF.

An important advantage of this technology is that it enables the use of digital multi-channel sound with sound cards that would otherwise be limited to PCM stereo or analog multi-channel sound.

DDL can be found under the components for the newer label "Dolby Home Theater". Devices with this label are capable of the following technologies: Dolby Pro Logic IIx, Dolby Headphone, Sound Space Expander, Natural Bass and Dolby Digital Live.

Television studios

Dolby Digital is primarily used in the consumer sector. In television studios, the Dolby Digital signal is only obtained from the Dolby E used in the studio immediately before broadcasting by means of transcoding . In contrast to Dolby E, Dolby Digital does not have an exact time alignment with the video signal, which is essential for video matrix switcher .


Dolby Digital EX

Dolby Digital 5.1 mark on DVD cases

Instead of the previous two rear channels, Dolby Digital EX supports three (rear right, rear center, rear left). This method is downward compatible, since the three return channels are not saved separately, but the central channel is formed from the left and right. It is thus similar to the analog Dolby Surround Pro Logic II.

Dolby Digital Plus

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

Dolby Digital on TV / radio

  • Digital television or radio reception via DVB or DAB is a prerequisite for using Dolby Digital .
  • September 18, 1999: Dolby Digital is supported by several program providers on television . ProSieben broadcast the first broadcast in Germany in this sound format on September 18, 1999 with the feature filmCourage to Truth ”. Today films are mostly broadcast in Dolby Digital 5.1 format. The rest of the program can be received in Dolby Digital 2.0 format. According to information from ProSieben, for example, the “ Super Bowl ” was previously broadcast in the USA in Dolby Digital 5.1.
  • January 1, 2003: In Austria , the ORF started broadcasting the New Year's Concert on January 1, 2003, also broadcasting Dolby Digital. As with ProSieben, films in this audio format are also regularly broadcast here.
  • On September 17, 2003, Sat.1 also began the first Dolby Digital tests. Here, too, feature films are regularly broadcast in this format. Sat.1 has already shown football games in Dolby Digital 5.1.
  • On October 4, 2003, Dolby Digital finally started on public broadcasters. The ZDF broadcast the show " Wetten, dass ..? “In Dolby Digital 5.1.
  • As of October 31, 2003, the Bavarian Broadcasting Corporation "Bayern 4 Klassik" will broadcast classical music every two weeks from 2:05 am to 4:00 am in Dolby Digital 5.1
  • September 3, 2004: The ORF started a Dolby Digital 5.1 radio test program on September 3, 2004. The first broadcast on the test channel was broadcast on the occasion of the "Long Night of Radio Art" of the radio program Ö1 . The program was broadcast on September 3, 2004 from 7:30 p.m. to 6:00 a.m. in Dolby Digital 5.1. Classical concerts - including live broadcasts from the Great Hall of the Musikverein in Vienna - are often broadcast in Dolby Digital 5.1 on this wave.
  • The concert series of the 36th Burghausen International Jazz Week began on August 7, 2005. BR-alpha was the first channel of the ARD network to broadcast all of the festival's concerts in the Dolby Digital 5.1 sound format.
  • On September 3, 2005, 3sat also broadcast for the first time as part of a broadcast from the Salzburg Festival in Dolby Digital 5.1 audio format.
  • Since 2005 the Bavarian broadcasting company “Bayern 4 Klassik” has been broadcasting live concerts from the Herkulessaal and the Gasteig in Munich in Dolby digital 5.1, since 2006 also the performances of the Bayreuth Festival. The other classic radio programs of the ARD follow. WDR3, hr2, SWR 2, MDR Figaro and NDR Kultur have also been broadcasting concerts in Dolby Digital 5.1 more frequently since then. In addition, these stations also transmit normal stereo programs in Dolby Digital 2.0, which means that the volume dynamics of the music are not compressed in contrast to VHF radio.
  • On December 12, 2005, ZDF broadcast a film for the first time ("The Time Machine") in Dolby Digital 5.1 audio format. ZDF has been broadcasting in Dolby Digital for a number of years, but mostly in stereo. A few “Wetten, dass ..?” Programs have already been broadcast in DD 5.1. In addition, the opening of the Allianz Arena was broadcast on ZDF in Dolby Digital 5.1.
  • December 14, 2005: ARD “Das Erste” begins broadcasting in Dolby Digital. According to Bayerischer Rundfunk, ARD will broadcast the program “Stars in der Manege” for the first time on December 26th with Dolby Digital 5.1 sound. The Saturday evening program “Understand Fun” will also be broadcast for the first time in Dolby Digital 5.1.
  • March 20, 2006: RTL Television begins broadcasting an additional Dolby Digital soundtrack via satellite. The first 5.1 broadcast is the feature film "Lord of the Rings - The Two Towers" on April 16, 2006.
  • July 15, 2008: Deluxe Music is the first music broadcaster to broadcast continuously in Dolby Digital 5.1. Since January 1, 2013, Deluxe Music no longer broadcasts in Dolby Digital, but only in stereo.
  • The HDTV offshoots of the private as well as the public television channels always carry a Dolby Digital stream with them (either stereo or 5.1). These are also those programs that only send an MP2 stream in SD format.

See also


  • Thomas Görne: Sound engineering. Fachbuchverlag Leipzig by Carl Hanser Verlag, Munich a. a. 2006, ISBN 3-446-40198-9 .
  • Roland Enders: The home recording manual. The way to optimal recordings. 3rd, revised edition. revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .

Web links

Commons : Dolby Digital  - collection of pictures, videos and audio files

Individual evidence

  1. Electronic Frontier Foundation: The patent on Dolby Digital (AC-3) has just expired. Retrieved June 19, 2018 .
  2. ^ Dolby History: 50 Years of Innovation. In: Retrieved May 12, 2016 .
  3. Dolby Digital Live ( Memento of the original from March 16, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ,  @1@ 2Template: Webachiv / IABot /
  4. Montego DDL ( Memento of the original from March 27, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ,  @1@ 2Template: Webachiv / IABot /
  6. HDA X-Plosion 7.1 DTS Connect ,
  7. NVIDIA nForce 500 motherboard reviews ,, June 8, 2006.