Dolby Digital

Dolby Digital 5.1AC3AC-3Dolby 5.1Dolby Digital 5.1 Surround SoundDolby Digital EX5.1Dolby Digital 5.1 SurroundDolby Digital LiveDolby AC-3
Dolby Digital, also known as Dolby AC-3, is the name for audio compression technologies developed by Dolby Laboratories.wikipedia
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Dolby Laboratories

DolbyDolby VisionDolby Labs
Dolby Digital, also known as Dolby AC-3, is the name for audio compression technologies developed by Dolby Laboratories. Dolby Laboratories adapted the MDCT algorithm along with perceptual coding principles to develop the AC-3 audio format for cinema needs.
Dolby Stereo Digital (now simply called Dolby Digital) was first featured on the 1992 film Batman Returns.

Discrete cosine transform

DCTiDCTinverse discrete cosine transform
It is a modification of the discrete cosine transform (DCT) algorithm, which was first proposed by Nasir Ahmed in 1972 and was originally intended for image compression.
It is used in most digital media, including digital images (such as JPEG and HEIF, where small high-frequency components can be discarded), digital video (such as MPEG, H.26x and Vorbis), digital audio (such as Dolby Digital, MP3 and AAC), digital television (such as SDTV, HDTV and VOD), digital radio (such as AAC+ and DAB+), and speech coding (such as AAC-LD, Siren and Opus).

Modified discrete cosine transform

MDCTModulated Lapped Transformtime-domain aliasing cancellation
Originally named Dolby Stereo Digital until 1994, except for Dolby TrueHD, the audio compression is lossy, based on the modified discrete cosine transform (MDCT) algorithm. The main basis of the Dolby AC-3 multi-channel audio coding standard is the modified discrete cosine transform (MDCT), a lossy audio compression algorithm.
It is employed in most modern audio coding standards, including MP3, Dolby Digital (AC-3), Vorbis (Ogg), Windows Media Audio (WMA), ATRAC, Cook, Advanced Audio Coding (AAC), LDAC, Dolby AC-4, MPEG-H 3D Audio, as well as speech coding standards such as AAC-LD (LD-MDCT), G.722.1, G.729.1, CELT, and Opus.

Sony

Sony CorporationSony ElectronicsSony Corp.
Dolby Digital was the earliest MDCT-based audio compression standard to be released, and was followed by other MDCT-based audio compression standards for home and portable usage, such as Sony's ATRAC (1992), the MP3 standard (1993) and AAC (1997).
In 1993, Sony challenged the industry standard Dolby Digital 5.1 surround sound format with a newer and more advanced proprietary motion picture digital audio format called SDDS (Sony Dynamic Digital Sound).

DTS (sound system)

DTSDatasat Digital 5.1DTS 5.1
Almost all current release cinema prints are of this type and may also include SDDS data and a timecode track to synchronize CD-ROMs carrying DTS soundtracks.
Work on the new audio format started in 1991, four years after Dolby Laboratories started work on its new codec, Dolby Digital.

Psychoacoustics

psychoacousticpsychoacoustic modelperceptual coding
Dolby Laboratories adapted the MDCT algorithm along with perceptual coding principles to develop the AC-3 audio format for cinema needs.
Some of these formats include Dolby Digital (AC-3), MP3, Opus, Ogg Vorbis, AAC, WMA, MPEG-1 Layer II (used for digital audio broadcasting in several countries) and ATRAC, the compression used in MiniDisc and some Walkman models.

Data compression

compressionvideo compressioncompressed
Dolby Digital, also known as Dolby AC-3, is the name for audio compression technologies developed by Dolby Laboratories. The main basis of the Dolby AC-3 multi-channel audio coding standard is the modified discrete cosine transform (MDCT), a lossy audio compression algorithm.
The MDCT is used by modern audio compression formats such as Dolby Digital, MP3, and Advanced Audio Coding (AAC).

Audio coding format

audio codingaudio coding standardaudio compression format
The main basis of the Dolby AC-3 multi-channel audio coding standard is the modified discrete cosine transform (MDCT), a lossy audio compression algorithm.
The MDCT is used by modern audio compression formats such as Dolby Digital, MP3, and Advanced Audio Coding (AAC).

LaserDisc

LDlaser discLaserVision
Early LaserDiscs featured in 1978 were entirely analog but the format evolved to incorporate digital stereo sound in CD format (sometimes with a TOSlink or coax output to feed an external DAC), and later multi-channel formats such as Dolby Digital and DTS.

Dolby Stereo

Dolby Stereo 70 mm Six Track70mm DolbyDolby A
Originally named Dolby Stereo Digital until 1994, except for Dolby TrueHD, the audio compression is lossy, based on the modified discrete cosine transform (MDCT) algorithm.
All release prints encoded with Dolby Digital include a Dolby SR analog soundtrack, both as a backup in case the digital track malfunctions and for theaters not equipped for Dolby Digital playback.

Lossy compression

lossylossy data compressioncompressed
Originally named Dolby Stereo Digital until 1994, except for Dolby TrueHD, the audio compression is lossy, based on the modified discrete cosine transform (MDCT) algorithm. The main basis of the Dolby AC-3 multi-channel audio coding standard is the modified discrete cosine transform (MDCT), a lossy audio compression algorithm.

Adaptive Transform Acoustic Coding

ATRACATRAC3ATRAC3plus
Dolby Digital was the earliest MDCT-based audio compression standard to be released, and was followed by other MDCT-based audio compression standards for home and portable usage, such as Sony's ATRAC (1992), the MP3 standard (1993) and AAC (1997).
ATRAC1 was first used in Sony's own theater format SDDS system in the 1990s, and in this context is a direct competitor to Dolby Digital (AC3) and DTS.

Stereophonic sound

StereoStereophonicstereo sound
Mono and stereo modes are also supported.
Dolby Stereo was succeeded by Dolby Digital 5.1 in the cinema, which retained the Dolby Stereo 70mm 5.1 channel layout, and more recently with the introduction of digital cinema, Dolby Surround 7.1 and Dolby Atmos in 2010 and 2012 respectively.

Dolby Surround 7.1

Dolby 7.1 Surround Sound
, Dolby Digital in film sound mixing is being gradually replaced with Dolby Surround 7.1, with the more advanced Dolby Atmos technology also gaining in popularity.
It adds two new channels to current Dolby Digital 5.1.

Surround sound

Surround5.1 surround sound5.1
EX adds an extension to the standard 5.1 channel Dolby Digital codec in the form of matrixed rear channels, creating 6.1 or 7.1 channel output.
Commercial surround sound media include videocassettes, DVDs, and SDTV broadcasts encoded as compressed Dolby Digital and DTS, and lossless audio such as DTS HD Master Audio and Dolby TrueHD on HDTV Blu-ray Disc and HD DVD, which are identical to the studio master.

Sony Dynamic Digital Sound

SDDSSony Digital 5.1Sony Dynamic Digital Sound (SDDS)
Almost all current release cinema prints are of this type and may also include SDDS data and a timecode track to synchronize CD-ROMs carrying DTS soundtracks.
SDDS was consistently the least popular of the three competing digital sound formats, the other two being Spectral Recording Dolby Stereo Digital and DTS.

Auzentech

Then in June 2005 came Auzentech, which with its X-Mystique PCI card, provided the first consumer sound card with Dolby Digital Live support.
Auzentech has its origins in March 2005, when under the company name HDA (HiTeC Digital Audio), the company launched the X-Mystique 7.1, the first consumer add-in sound card to feature Dolby Digital Live.

Home cinema

home theaterhome theatrehome theater system

Subwoofer

subwooferssub-woofersub
The most elaborate mode in common use involves five channels for normal-range speakers (20 Hz – 20,000 Hz) (right, center, left, right surround, left surround) and one channel (20 Hz – 120 Hz allotted audio) for the subwoofer driven low-frequency effects.
In 1992, Dolby Digital's six-channel film sound format incorporated a single LFE channel, the "point one" in 5.1 surround sound.

HDMI

High-Definition Multimedia InterfaceHDMI 1.4HDMI 2.0
HDMI was later introduced, and it can carry uncompressed multichannel PCM, lossless compressed multichannel audio, and lossy compressed digital audio.
HDMI also carries any IEC 61937-compliant compressed audio stream, such as Dolby Digital and DTS, and up to 8 channels of one-bit DSD audio (used on Super Audio CDs) at rates up to four times that of Super Audio CD.

SoundStorm

The SoundStorm, used for the Xbox game console and certain nForce2 motherboards, used an early form of this technology.
It was also necessary to meet certain sound quality levels as tested by Dolby Digital sound labs.

35 mm movie film

35 mm35mm35mm film
Dolby Digital cinema soundtracks are optically recorded on a 35 mm release print using sequential data blocks placed between every perforation hole on the sound track side of the film.
They are: Dolby Digital, which is stored between the perforations on the sound side; SDDS, stored in two redundant strips along the outside edges (beyond the perforations); and DTS, in which sound data is stored on separate compact discs synchronized by a timecode track on the film just to the right of the analog soundtrack and left of the frame.

Low-frequency effects

LFELow Frequency Effectsbass
The most elaborate mode in common use involves five channels for normal-range speakers (20 Hz – 20,000 Hz) (right, center, left, right surround, left surround) and one channel (20 Hz – 120 Hz allotted audio) for the subwoofer driven low-frequency effects.
Later formats such as Dolby Digital retained the LFE channel, although this is more through convention and backwards compatibility than necessity, as digital formats have greater dynamic range than the magnetic analogue recordings on 70 mm prints, and modern sound processors have a bass management system to redirect bass from all channels to a subwoofer.

S/PDIF

SPDIFIEC 61937digital audio output
It converts any audio signals on a PC or game console into a 5.1-channel 16-bit/48 kHz Dolby Digital format at 640 kbit/s and transports it via a single S/PDIF cable.
This mode is used to connect the output of a DVD player or computer, via optical or coax, to a home theatre amplifying receiver that supports Dolby Digital or DTS.

5.1 surround sound

5.15.1 surround5.1 channel
EX adds an extension to the standard 5.1 channel Dolby Digital codec in the form of matrixed rear channels, creating 6.1 or 7.1 channel output.
Dolby Digital, Dolby Pro Logic II, DTS, SDDS, and THX are all common 5.1 systems.