Dolby Pro Logic is a
surround sound
Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener ( surround channels). Its first application was in movie theaters. Prior to sur ...
processing technology developed by
Dolby Laboratories
Dolby Laboratories, Inc. (often shortened to Dolby Labs and known simply as Dolby) is an American company specializing in Noise reduction#In audio, audio noise reduction, Audio data compression, audio encoding/compression, spatial audio, and ...
, designed to decode soundtracks encoded with Dolby Surround.
Dolby Stereo
Dolby Stereo is a sound format made by Dolby Laboratories. It is a unified brand for two completely different basic systems: the Dolby SVA (stereo variable-area) 1976 system used with optical sound tracks on 35mm film, and Dolby Stereo 70mm nois ...
(also known as ''Dolby MP'' or ''Dolby SVA'') was developed by Dolby in 1976 for analog
cinema
Cinema may refer to:
Film
* Cinematography, the art of motion-picture photography
* Film or movie, a series of still images that create the illusion of a moving image
** Film industry, the technological and commercial institutions of filmmaking
...
sound systems. The format was adapted for home use in 1982 as Dolby Surround when
HiFi capable consumer
VCR
A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the recording. ...
s were introduced. It was further improved with the Dolby Pro Logic decoding system after 1987.
The ''Dolby MP Matrix'' was the professional system that encoded four channels of film sound into two. This track used by the ''Dolby Stereo'' theater system on a 35mm optical stereo print and decoded back to the original 4.0 Surround. The same four-channel encoded stereo track was largely left unchanged and made available to consumers as ''"Dolby Surround"'' on home video. However, the original Dolby Surround decoders in 1982 were a simple passive matrix three-channel decoder: L/R and Mono Surround. The surround was limited to 7kHz. It also had
Dolby Noise Reduction
A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. The first was '' Dolby A'', a professional broadband noise reduction ...
and an adjustable delay for improved channel separation and to prevent dialog leaking and arriving to listeners' ears first. The front center channel was equally split between the left and right channels for phantom center reproduction. This differed from the Cinema Dolby Stereo system which used active steering and other processing to decode a center channel for dialog and center focused on screen action.
Later on in 1987, the Pro Logic decoding system was released to consumers. It featured virtually the same type of four-channel decoding as the Dolby Stereo theater processor with active steering logic and much better channel separation (up to 30dB) as well as including a dedicated center channel output for the first time. Many standalone Pro Logic decoders also included a phantom center option for compatibility with earlier non-Pro Logic Dolby Surround equipped home theaters to split the center channel signal to the L/R speakers for legacy phantom center reproduction.
''Dolby Surround Pro Logic'' is the full name that refers to the matrix surround format and decoding system in one. When a Dolby Surround soundtrack is created in post production (''Dolby MP Matrix''), four channels of sound are matrix-encoded into an ordinary
stereo
Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...
(two-channel) soundtrack. The center channel is encoded by placing it equally in the left and right channels minus 3dB; and the surround channel is encoded using
phase shift
In physics and mathematics, the phase of a periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is denoted \phi(t) and expressed in such a scale that it v ...
techniques for out of phase information (L-R). The surround channel was often used for ambient background sounds in the original recording, music scores and effects.
A Dolby Pro Logic decoder/processor "unfolds" the soundtrack back into its original 4.0 surround—left and right,
center
Center or centre may refer to:
Mathematics
*Center (geometry), the middle of an object
* Center (algebra), used in various contexts
** Center (group theory)
** Center (ring theory)
* Graph center, the set of all vertices of minimum eccentrici ...
, and a single limited frequency-range (7 kHz
low-pass filter
A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter des ...
ed
) 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. One of the first was the MSP400 surround sound receiver and amplifier by RCA for their high-end
Dimensia
''Dimensia'' was RCA's brand name for their high-end models of television systems and their components ( Tuner, VCR, CD Player, etc.) produced from 1984 to 1989, with variations continuing into the early 1990s, superseded by the ProScan model li ...
brand. It was released in 1987 for the
Digital Command Component System.
Dolby Surround
''Dolby Surround'' is the earliest consumer version of
Dolby's surround sound decoding technology. It was introduced to the public in 1982 during the time home video recording formats (such as
Betamax
Betamax (also known as Beta, as in its logo) is a consumer-level analog recording and cassette format of magnetic tape for video, commonly known as a video cassette recorder. It was developed by Sony and was released in Japan on May 10, 1975, ...
and
VHS) were introducing
Stereo
Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...
and
HiFi capability. The name Dolby Surround described the consumer passive matrix decoding technology; the professional, active-matrix cinema technology bore the name
Dolby Stereo
Dolby Stereo is a sound format made by Dolby Laboratories. It is a unified brand for two completely different basic systems: the Dolby SVA (stereo variable-area) 1976 system used with optical sound tracks on 35mm film, and Dolby Stereo 70mm nois ...
. It was capable of decoding Dolby Stereo four-channel soundtracks to three output channels (Left, Right, Surround). The Center channel was fed equally to the Left and Right speakers. The Surround channel was limited to a 100 Hz to 7 kHz frequency bandwidth, as dialog from the center channel could leak into the surround channel - there was as little as 3 dB of separation between LCR and Surround channels.
Dolby Pro Logic
In 1987 the decoding technology was updated and renamed ''Dolby Pro Logic''.
A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right,
center
Center or centre may refer to:
Mathematics
*Center (geometry), the middle of an object
* Center (algebra), used in various contexts
** Center (group theory)
** Center (ring theory)
* Graph center, the set of all vertices of minimum eccentrici ...
, and a single limited frequency-range (7 kHz
low-pass filter
A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter des ...
ed
) mono rear channel.
A Pro Logic decoder also uses 'Steering Logic', which drives amplifiers, to raise or lower the output volume of each channel based on the current dominant sound direction. For example, while a mono signal is played, the strong correlation to the center channel triggers the output volume of the left, right and surround channels to be lowered. This increases the channel separation achievable, to around 30 decibels between channels. By careful tuning of the response of the amplifiers, the total amount of signal energy remains constant and is unaffected by the operation of the channel steering. Additionally, the response time of the system to changes in sound direction is important as too fast a response results in a twitchy feel, while too slow a response leaves sounds coming from an inappropriate direction.
In addition to 5db of noise processing, the surround channel is slightly delayed, so that any front channel sounds that leak into the surround channel arrive at the listener after the front channels. This takes advantage of the
Haas effect
Haas may refer to:
People
* Haas (surname)
* Haas Visser 't Hooft (1905–1977), Dutch field hockey player
Auto racing
* Haas F1 Team, a 21st-century Formula 1 auto racing team
* Haas Lola, a 20th-century Formula 1 auto racing team
* Newman/Haa ...
- audio that is present in the front speakers but delayed in the surround speakers will have the psychoacoustic effect of emanating from the front of the sound stage.
Dolby Surround and Dolby Pro Logic decoders are similar in principle, as both use matrix technology to extract extra channels from Dolby Stereo stereo-encoded audio. The terms Dolby Stereo, Dolby Surround and Lt/Rt are all used to describe soundtracks that are matrix-encoded using this technique.
Dolby Pro Logic II
![Dolby-Surround-Pro-Logic-II](https://upload.wikimedia.org/wikipedia/commons/9/9e/Dolby-Surround-Pro-Logic-II.svg)
In 2000, Dolby introduced ''Dolby Pro Logic II'' (DPL II), an improved implementation of Dolby Pro Logic created by
Jim Fosgate
James M. Fosgate (born December 5, 1937 in Indianapolis, Indiana) was an American inventor, engineer and businessman. The self-taught son of a television and radio repairman, Fosgate invented the first car amplifier in 1973 and founded Fosgate E ...
. DPL II processes any high-quality stereo signal source into five separate full frequency channels (right front, center, left front, right rear and left rear), while also decoding five 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 five-channel surround sound.
Because of the limited nature of the original DPL, many consumer electronics manufacturers 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
Servo may refer to:
Mechanisms
* Servomechanism, or servo, a device used to provide control of a desired operation through the use of feedback
** AI servo, an autofocus mode
** Electrohydraulic servo valve, an electrically operated valve that c ...
(
negative feedback
Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused by ...
) circuits used to derive five channels. The extra channel content is extracted using the difference between the spatial audio content between two individual channels of stereo tracks or Dolby Digital encoded 5.1 channel tracks and outputs it appropriately.
In addition to five full-range playback channels, Pro Logic II introduced a Music mode that includes optimized channel delays and adds user controls to—for example—adjust apparent sound stage width.
Pro Logic II systems also feature a mode designed specifically for
video gaming
Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, controller, keyboard, or motion sensing device to generate visual feedback. This feedback m ...
, and was frequently used in game titles for Sony's
PlayStation 2
The PlayStation 2 (PS2) is a home video game console developed and marketed by Sony Computer Entertainment. It was first released in Japan on 4 March 2000, in North America on 26 October 2000, in Europe on 24 November 2000, and in Australia on 3 ...
, Nintendo's
GameCube
The is a home video game console developed and released by Nintendo in Japan on September 14, 2001, in North America on November 18, 2001, and in PAL territories in 2002. It is the successor to the Nintendo 64 (1996), and predecessor of the Wii ...
and
Wii
The Wii ( ) is a home video game console developed and marketed by Nintendo. It was released on November 19, 2006, in North America and in December 2006 for most other Regional lockout, regions of the world. It is Nintendo's fifth major ho ...
as an alternative to digital surround formats such as
Dolby Digital
Dolby Digital, originally synonymous with Dolby AC-3, is the name for what has now become a family of audio compression technologies developed by Dolby Laboratories. Formerly named Dolby Stereo Digital until 1995, the audio compression is lossy ...
, or
DTS. Game mode is similar to Movie mode, except it redirects more bass to the LFE channel.
Dolby Pro Logic IIx
A newer ''Dolby Pro Logic IIx'' system is also now available, which can take two-channel stereo, Dolby Surround (sometimes called Dolby Stereo Surround) and Dolby Digital 5.1 source material and up-convert it to 6.1 or
7.1 channel surround sound.
Dolby Pro Logic IIz
''Dolby Pro Logic IIz'' expands on Pro Logic IIx with the addition of a height component, creating front
height channel
Height channels are audio channels in surround sound multichannel audio. Height channels are located above the listening area and increase the sound field beyond the horizontal plane.
Two systems that use height channels, Dolby Pro Logic IIz and ...
s above the front left and right speakers, expanding a 5.1 or 7.1 system to 7.1 Height or 9.1. It identifies spatial cues in low-level, uncorrelated information, such as ambience and effects like rain or wind in the side and rear surround channels, and directs it to the front height speakers. The channels it adds are matrixed, not discrete.
Dolby Surround (2014)
Dolby reintroduced the ''Dolby Surround'' terminology in 2014 to refer to something entirely new. The term now refers to a new upmixer whose purpose is to enable
Atmos receivers and speaker configurations to serve non-Atmos signals.
''Dolby Surround'' is a complete replacement for Pro Logic that upmixes stereo and multi-channel inputs to play over Atmos configurations.
Software encoding and decoding
* The
liba52
MPlayer is a free and open-source media player software application. It is available for Linux, OS X and Microsoft Windows. Versions for OS/2, Syllable, AmigaOS, MorphOS and AROS Research Operating System are also available. A port for DOS u ...
decoder library for AC3 and A52 digital sound optionally exports Lt/Rt stereo sound compatible with Pro Logic decoders.
*
HandBrake and
FFmpeg
FFmpeg is a free and open-source software project consisting of a suite of libraries and programs for handling video, audio, and other multimedia files and streams. At its core is the command-line ffmpeg tool itself, designed for processing of vid ...
are capable of downmixing Dolby Digital AC-3 5.1 to Lt/Rt stereo tracks compatible with Dolby Pro Logic I & II decoders.
* SurCode for Dolby Pro Logic II is a Dolby-certified software encoder and decoder available in plug-in formats for
DAWs and as a standalone application.
Hardware encoding
* Dolby Digital (AC3) compatible hardware (DVDs, TVs, Blu-ray players) downmixes the 5.1 channel tracks into Lt/Rt stereo compatible with Pro Logic decoders
See also
*
Dolby encoding and decoding matrices
*
Dolby Digital
Dolby Digital, originally synonymous with Dolby AC-3, is the name for what has now become a family of audio compression technologies developed by Dolby Laboratories. Formerly named Dolby Stereo Digital until 1995, the audio compression is lossy ...
*
Dolby Atmos
Dolby Atmos is a surround sound technology developed by Dolby Laboratories. It expands on existing surround sound systems by adding height channels, allowing sounds to be interpreted as three-dimensional objects with neither horizontal, nor verti ...
*
DTS Neo:6
*
AV receiver
An audio/video receiver (AVR) is a consumer electronics component used in a home theater. Its purpose is to receive audio and video signals from a number of sources, and to process them and provide power amplifiers to drive loudspeakers and ro ...
*
Surround sound
Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener ( surround channels). Its first application was in movie theaters. Prior to sur ...
References
External links
Dolby's official siteHome theatre focus' history of dolby surround decoders{{Dolby Laboratories
Film sound production
Surround sound
Dolby Laboratories
Audiovisual introductions in 1986
American brands