Dolby Pro Logic
Encyclopedia
Dolby Pro Logic is a surround sound
processing technology developed by Dolby Laboratories
, designed to decode soundtracks encoded with Dolby Surround
. Dolby Stereo
was originally developed by Dolby 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 introduced; it 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 and 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.
technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into an ordinary stereo
(two channel) sound track. The centre channel is encoded by placing it equally in the left and right channels; the rear channel is encoded using phase shift techniques, typically an out of phase stereo
mixdown. A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center
, and a single limited frequency-range (7 kHz low-pass filter
ed) mono rear channel—while systems lacking the decoder play back the audio as standard stereo.
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, providing an illusion of greater separation.
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 brand. It was released in 1987 for the Digital Command Component System.
. 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). Dolby Pro Logic II also decodes 5 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 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
(negative feedback
) 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 which includes optimized channel delays, and adds user controls to - for example - adjust apparent front sound stage width.
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 surround formats such as Dolby Digital
, or DTS.
and Pro Logic.
HandBrake
is capable of downmixing Dolby Digital AC-3 5.1 to Stereo for Dolby Pro Logic I & II for surround playback.
Minnetonka Audio's SurCode for Dolby Pro Logic II is capable of encoding LPCM files into Dolby Pro Logic I & II for surround playback.
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, Dolby Surround only decodes the rear surround channel, while Dolby Pro Logic also decodes the center channel
. 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.
Surround sound
Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...
processing technology developed by Dolby Laboratories
Dolby Laboratories
Dolby Laboratories, Inc. , often shortened to Dolby Labs, is an American company specializing in audio noise reduction and audio encoding/compression.-History:...
, designed to decode soundtracks encoded with Dolby Surround
Dolby Surround
Dolby Surround was the earliest consumer version of Dolby's multichannel analog film sound decoding format Dolby Stereo introduced to the public in 1982 during the time home video recording formats were introducing Stereo and HiFi capability...
. Dolby Stereo
Dolby Stereo
Dolby Stereo, is the trade mark that Dolby Laboratories used for the various analogue stereo cinema sound formats that they produced.Two basic systems used this name. The first was the 'Dolby SVA' system used with optical soundtracks on 35mm film...
was originally developed by Dolby in 1976 for analog cinema
Movie theater
A movie theater, cinema, movie house, picture theater, film theater is a venue, usually a building, for viewing motion pictures ....
sound systems. The format was adapted for home use in 1982 as Dolby Surround
Dolby Surround
Dolby Surround was the earliest consumer version of Dolby's multichannel analog film sound decoding format Dolby Stereo introduced to the public in 1982 during the time home video recording formats were introducing Stereo and HiFi capability...
when HiFi capable consumer VCRs were introduced; it was then replaced by the newer and improved Pro-Logic system in 1987. However, the term "Dolby Surround
Dolby Surround
Dolby Surround was the earliest consumer version of Dolby's multichannel analog film sound decoding format Dolby Stereo introduced to the public in 1982 during the time home video recording formats were introducing Stereo and HiFi capability...
" is still used to describe the encoding technology or matrix-encoded soundtrack, whereas Pro Logic refers to the decoding technology and 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
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
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 matrixMatrix decoder
Matrix decoder is an audio technology where a finite number of discrete audio channels are decoded into a larger number of channels on play back...
technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into an ordinary stereo
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
(two channel) sound track. The centre channel is encoded by placing it equally in the left and right channels; the rear channel is encoded using phase shift techniques, typically an out of phase stereo
Out Of Phase Stereo (OOPS)
Out Of Phase Stereo is an audio technique which manipulates the phase of a stereo audio track, to isolate or remove certain components of the stereo mix...
mixdown. A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center
Center channel
Center channel refers to an audio channel common to many surround sound formats. It is the channel that is mostly, or fully, dedicated to the reproduction of the dialogue of an audiovisual program...
, and a single limited frequency-range (7 kHz low-pass filter
Low-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
ed) mono rear channel—while systems lacking the decoder play back the audio as standard stereo.
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, providing an illusion of greater separation.
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 brand. It was released in 1987 for the Digital Command Component System.
Dolby Pro Logic II
In 2000, Dolby introduced Dolby Pro Logic II (DPL II), an improved implementation of Dolby Pro Logic created by Jim FosgateJim Fosgate
James M. "Jim" Fosgate is 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 Electronics, now called Rockford Fosgate...
. 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). Dolby Pro Logic II also decodes 5 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 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
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
(negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
) 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 which includes optimized channel delays, and adds user controls to - for example - adjust apparent front sound stage width.
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
PlayStation 2
The PlayStation 2 is a sixth-generation video game console manufactured by Sony as part of the PlayStation series. Its development was announced in March 1999 and it was first released on March 4, 2000, in Japan...
, Nintendo's GameCube
Nintendo GameCube
The , officially abbreviated to NGC in Japan and GCN in other regions, is a sixth generation video game console released by Nintendo on September 15, 2001 in Japan, November 18, 2001 in North America, May 3, 2002 in Europe, and May 17, 2002 in Australia...
and Wii
Wii
The Wii is a home video game console released by Nintendo on November 19, 2006. As a seventh-generation console, the Wii primarily competes with Microsoft's Xbox 360 and Sony's PlayStation 3. Nintendo states that its console targets a broader demographic than that of the two others...
as an alternative to digital surround formats such as Dolby Digital
Dolby Digital
Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints...
, or DTS.
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 IIx also takes signals intended for Dolby Pro Logic II and up-converts them to a 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 channels 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, and directs it to the front height speakers. The channels it adds are matrixed, not discrete.Software encoding
The liba52 decoder library for AC3 and A52 digital sound optionally exports stereo sound compatible with Dolby SurroundDolby Surround
Dolby Surround was the earliest consumer version of Dolby's multichannel analog film sound decoding format Dolby Stereo introduced to the public in 1982 during the time home video recording formats were introducing Stereo and HiFi capability...
and Pro Logic.
HandBrake
HandBrake
HandBrake is a general-purpose, open-source, cross-platform, multithreaded video transcoder software application. HandBrake was originally developed by titer in 2003 as a general-purpose video transcoder to make ripping a film from a DVD to a data storage device easier...
is capable of downmixing Dolby Digital AC-3 5.1 to Stereo for Dolby Pro Logic I & II for surround playback.
Minnetonka Audio's SurCode for Dolby Pro Logic II is capable of encoding LPCM files into 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 SurroundDolby Surround
Dolby Surround was the earliest consumer version of Dolby's multichannel analog film sound decoding format Dolby Stereo introduced to the public in 1982 during the time home video recording formats were introducing Stereo and HiFi capability...
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, Dolby Surround only decodes the rear surround channel, while Dolby Pro Logic also decodes the center channel
Center channel
Center channel refers to an audio channel common to many surround sound formats. It is the channel that is mostly, or fully, dedicated to the reproduction of the dialogue of an audiovisual program...
. 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.
Dolby Surround at a glance
| Decoder | Encoder | Year | Description | Channels |
|---|---|---|---|---|
| Dolby Stereo | 1975 | Cinema use with optical technology. Uses Dolby A for noise reduction. Upmix stereo to Surround 4.0 | FL FR with C and MonoSurround matrixed | |
| Dolby Surround | Dolby Surround | 1982 | First Home use. Analog. Upmix stereo to Surround 3.0 | FL FR and MonoSurround matrixed |
| Dolby Stereo SR | 1986 | Cinema use. Uses Dolby SR for noise reduction. | FL FR with C and MonoSurround matrixed | |
| Dolby Pro Logic | 1987 | Improved Dolby Surround. Upmix Stereo to Surround 4.0. | FL FR with C and MonoSurround matrixed | |
| Dolby Digital | AC3 | 1992 Film 1995 Laser Disc |
Discrete channel encoder/decoder. Pro Logic Decoder can be used for downmixed stereo inputs. | FL FR C SL SR SUB |
| Dolby Digital EX/Dolby Digital Surround EX | 1999 | non-discrete 6.1 or 7.1 (5.1 with Center Rear matrixed onto SL & SR) | FL FR C SL SR (with matrixed RearMono) SUB [non-discrete 7.1: BackLeft and BackRight] | |
| Dolby Pro Logic II |
2000 | Improved Dolby Pro Logic. Upmix Stereo to Surround 5.1 in either Movie, Music, or Game mode. | FL FR C SL SR SUB | |
| Dolby Pro Logic IIx | 2002 | Upmix Stereo or Surround 5.1 to 6.1 or 7.1 in either Movie, Music, or Game mode. | FL FR C SL SR SUB Left Back and Right Back | |
| Dolby Digital Plus Dolby Digital Plus Dolby Digital Plus is a digital audio compression scheme. It is an incompatible development of the technologies used in the earlier Dolby Digital system. E-AC-3 has a number of improvements aimed at increasing quality at a given bitrate compared with legacy Dolby Digital... |
High bitrate version of Dolby Digital EX. Currently uses 7.1 channels with support for up to 13. | FL FR C SL SR SUB Left Back and Right Back | ||
| Dolby TrueHD Dolby TrueHD Dolby TrueHD is an advanced lossless multi-channel audio codec developed by Dolby Laboratories which is intended primarily for high-definition home-entertainment equipment such as Blu-ray Disc and HD DVD. It is the successor to the AC-3 Dolby Digital surround sound codec which was used as the... |
Lossless encoder for High Definition Video Sound. Eight full-range channels of 24-bit/96 kHz. Higher Bitrate than DD-Plus. | |||
| Dolby Pro Logic IIz | 2009 | Upmix Stereo or Surround 5.1/7.1 to 7.1 Height or 9.1 with the addition of front height channels. (Based on Dolby Pro Logic IIx.) | L, C, R, Ls, Rs, Lrs (Left Back), Rrs (Right Back), LFE, Lvh and Rvh |
Dolby encoding matrices
Note that j represents a 90° ( radians) phase shift.| Dolby Surround | Left | Right | Surround |
|---|---|---|---|
| Left Total |  |
 |
 |
| Right Total |  |
 |
 |
| Dolby Pro Logic | Left | Right | Center | Rear |
|---|---|---|---|---|
| Left Total |  |
 |
 |
 |
| Right Total |  |
 |
 |
 |
| Dolby Pro Logic II | Left | Right | Center | Rear Left | Rear Right |
|---|---|---|---|---|---|
| Left Total |  |
 |
 |
 |
 |
| Right Total |  |
 |
 |
 |
 |
See also
- Dolby DigitalDolby DigitalDolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints...
- DTS Neo:6
- AV Receivers
- Surround soundSurround soundSurround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...