Dolby Stereo
Encyclopedia
Two basic systems used this name. The first was the 'Dolby SVA' (stereo variable area) system used with optical soundtracks on 35mm film. The second was Dolby Stereo 70mm, which referred to Dolby noise reduction on the 6-channel magnetic soundtracks on 70mm prints.
Dolby SVA
Of the two, Dolby SVA was by far the more significant, as it brought high-quality stereo sound within the reach of virtually every cinema. Though stereo magnetic sound had been used on film since the 1950s, the technology had proved expensive and unreliable. The majority of movie theatres did not have facilities for playing back magnetic soundtracks, and the vast majority of films continued to be produced with mono optical soundtracks. Dolby SVA provided a way out of this impasse by putting a high-quality stereo soundtrack on optical sound prints.The optical soundtrack on a Dolby Stereo encoded 35 mm film not only carried left and right tracks for stereophonic sound
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...
, but also—through a matrix decoding system similar to those developed for "quadraphonic
Quadraphonic
Quadraphonic sound – the most widely used early term for what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are independent of one another...
" or "quad" sound in the 1970s)—a third 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...
, and a fourth surround channel for speakers on the sides and rear of the theater for ambient sound and special effects. This yielded a total of four sound channels in the track space previously allocated for one mono optical channel. Dolby also incorporated its A-Type noise reduction into the Dolby Stereo process. The brand of Dolby Stereo became a world leader, and synonymous with high quality sound in thousands of movie theaters across the world.
History
Dolby Lab's original involvement in movie sound was when film studios used Dolby A type noise reduction on studio magnetic film recordings. The first film that used Dolby noise reduction throughout the production process was "A Clockwork OrangeA Clockwork Orange (film)
A Clockwork Orange is a 1971 film adaptation of Anthony Burgess's 1962 novel of the same name. It was written, directed and produced by Stanley Kubrick...
," though much of the benefit was lost when it was released with a standard "Academy" optical soundtrack. This led to a proposal from Dolby that A type noise reduction be applied to the optical soundtrack on release prints.
At that time (early 1970s) there was renewed interest in improving the quality of optical soundtracks, which had changed little since the 1930s. In particular the infamous "Academy curve" was still in use. This curve was the standard frequency response for cinema playback of optical tracks as specified by the Academy of Motion Picture Arts and Sciences
Academy of Motion Picture Arts and Sciences
The Academy of Motion Picture Arts and Sciences is a professional honorary organization dedicated to the advancement of the arts and sciences of motion pictures...
in 1938, it involved a drastic roll-off in the high-frequency response of the theatre system with the intention of reducing the audibility of noise and distortion. Dolby proposed ditching the Academy curve and instead using Dolby A type noise reduction on the track. Starting with the 1974 film Callan, ten films were released with a Dolby encoded mono soundtrack. Dolby made available a unit for installation in cinemas that included a Dolby A type noise reduction module and a 3rd octave equaliser to equalise the electro-acoustic frequency response of the speakers/auditorium to a new international standard for movie theatres
Although this system worked well it made little impact on theatre owners who were disinclined to spend the necessary money for what seemed to them a relatively small improvement. Something more was needed to get them to dig their hands in their pockets, and that something extra was stereo.
Eastman Kodak
Eastman Kodak
Eastman Kodak Company is a multinational imaging and photographic equipment, materials and services company headquarted in Rochester, New York, United States. It was founded by George Eastman in 1892....
and RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
had been working on a stereo variable area system since 1973, Dolby Labs now joined them and added their noise reduction process to the Kodak/RCA SVA system. Dolby also suggested employing a matrix similar to those currently being used for domestic "Quadraphonic
Quadraphonic
Quadraphonic sound – the most widely used early term for what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are independent of one another...
" systems; by this means it was possible to provide a four channel stereo system using the same speaker layout as had been used for the CinemaScope
CinemaScope
CinemaScope was an anamorphic lens series used for shooting wide screen movies from 1953 to 1967. Its creation in 1953, by the president of 20th Century-Fox, marked the beginning of the modern anamorphic format in both principal photography and movie projection.The anamorphic lenses theoretically...
4-track magnetic stereo system of the 1950s but at far lower cost. Dolby Stereo, as this system was now branded, was first used on the 1975 Ken Russell
Ken Russell
Henry Kenneth Alfred "Ken" Russell was an English film director, known for his pioneering work in television and film and for his flamboyant and controversial style. He attracted criticism as being obsessed with sexuality and the church...
film Lisztomania, in a 3-channel Left, Centre, Right configuration. In the following year A Star is Born
A Star Is Born (1976 film)
A Star Is Born is a 1976 American rock music musical film telling the story of a young woman, played by Barbra Streisand who enters show business, and meets and falls in love with an established male star, played by Kris Kristofferson, only to find her career ascending while his goes into decline...
was the first film to use the full 4-channel Dolby Stereo system. Initially the Sansui QS matrix was used, but from the Spring of 1979 onwards a new custom-designed matrix was employed. This new matrix was first used for Hair
Hair (film)
Hair is a 1979 American film adaptation of the 1968 Broadway musical of the same name about a Vietnam war draftee who meets and befriends a tribe of long-haired hippies on his way to the army induction center...
and Hurricane
Hurricane (1979 film)
Hurricane is a 1979 romance, epic-adventure film featuring an all-star cast and impressive special effects, produced by: Dino De Laurentiis and Lorenzo Semple Jr, and directed by Jan Troell...
.
The success of 1977's Star Wars
Star Wars
Star Wars is an American epic space opera film series created by George Lucas. The first film in the series was originally released on May 25, 1977, under the title Star Wars, by 20th Century Fox, and became a worldwide pop culture phenomenon, followed by two sequels, released at three-year...
, which used the four channel system to great effect, did much to encourage movie theaters to convert to the 4-channel LCRS speaker configuration. The 1979 re-release of 101 Dalmatians was the first Disney Classics film to use Dolby Stereo.
A key feature of this system was its backward-compatibility: the same print could play anywhere, from an old drive-in theater with mono sound to a cinema that had upgraded to a Dolby Stereo processor. Thus, there was no need (nor expense) in carrying a double inventory of prints for distribution. The success of Dolby Stereo resulted in the final demise of magnetic stereo on 35mm release prints. From then on, only 70mm prints used magnetic sound.
Dolby SR noise reduction began to replace Dolby A type NR in 35 mm motion picture exhibition from the early 1990s onwards. A Dolby SR analogue soundtrack is still included on all theatrical release prints encoded with 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...
, as the default track if something goes wrong with decoding the digital track. Also the Dolby SR track is used in theaters not equipped for Dolby Digital playback.
The Dolby Stereo Matrix
The Dolby Stereo Matrix is straightforward: the four original channels: Left (L), Center (C), Right (R), and Surround (S), are combined into two, known as Left-total (LT) and Right-total (RT) by this formula:-| Dolby Stereo Mix | Left | 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... | Surround |
|---|---|---|---|---|
| Left Total |  |
 |
 |
 |
| Right Total |  |
 |
 |
 |
where j = +90° phase-shift
Thus center channel information is carried by both LT and RT in phase, and surround channel information by both LT and RT but out of phase. This gives good compatibility with both mono playback, which reproduces L, C and R from the mono speaker with C at a level 3dB higher than L or R, but surround information cancels out. It also gives good compatibility with two-channel stereo playback where C is reproduced from both left and right speakers to form a phantom center and surround is reproduced from both speakers but in a diffuse manner.
A simple 4-channel decoder could simply send the sum signal (L+R) to the center speaker, and the difference signal (L-R) to the surrounds. But such a decoder would provide poor separation between adjacent speaker channels, thus anything intended for the center speaker would also reproduce from left and right speakers only 3dB below the level in the center speaker. Similarly anything intended for the left speaker would be reproduced from both the center and surround speakers, again only 3dB below the level in the left speaker. There is, however complete separation between left and right, and between center and surround channels.
To overcome this problem the cinema decoder uses so-called "logic" circuitry to improve the separation. The logic circuitry decides which speaker channel has the highest signal level and gives it priority, attenuating the signals fed to the adjacent channels. Because there already is complete separation between opposite channels there is no need to attenuate those, in effect the decoder switches between L and R priority and C and S priority. This places some limitations on mixing for Dolby Stereo and to ensure that sound mixers mixed soundtracks appropriately they would monitor the sound mix via a Dolby Stereo encoder and decoder in tandem. In addition to the logic circuitry the surround channel is also fed via a delay, adjustable up to 100msec to suit auditoria of differing sizes, to ensure that any leakage of program material intended for left or right speakers into the surround channel is always heard first from the intended speaker. This exploits the "Precedence effect
Precedence effect
The precedence effect or law of the first wavefront is a binaural psychoacoustic effect. It means: If the same sound signal arrives time delayed at a listener from different directions, only the direction of the first arriving sound signal is perceived...
" to localise the sound to the intended direction.
Dolby Stereo 70 mm Six Track
Dolby Stereo 70 mm Six Track refers to the use of Dolby noise reduction on the six magnetic soundtracks of a 70 mm70 mm film
70mm film is a wide high-resolution film gauge, with higher resolution than standard 35mm motion picture film format. As used in camera, the film is wide. For projection, the original 65mm film is printed on film. The additional 5mm are for magnetic strips holding four of the six tracks of sound...
print. This was first used on some prints of the MGM film Logan's Run
Logan's Run
Logan's Run is a novel by William F. Nolan and George Clayton Johnson. Published in 1967, it depicts a dystopic ageist future society in which both population and the consumption of resources are maintained in equilibrium by requiring the death of everyone reaching a particular age...
released in 1976.
The Todd-AO
Todd-AO
Todd-AO is a post-production company founded in 1953, providing sound-related services to the motion picture and television industries. The company operates three facilities in the Los Angeles area.-History:...
70mm format was introduced in 1955 and included multi-channel magnetic sound from the start, it does not have an optical soundtrack (although in recent years some 70mm prints have used an optical digital track in place of the analogue magnetic one).
The original layout was for 5 front channels and one surround. But by the 1970s the use of the intermediate (left-center and right-center) tracks had been largely abandoned, these channels either being left blank, or filled with a simple mix of the adjacent channels. Dolby did not approve of this later practice, which results in loss of separation, but instead used these channels for LFE (low-frequency enhancement) utilising the bass units of the otherwise redundant intermediate front speakers. Later the unused HF capacity of these channels was used to provide for stereo surround in place of the mono surround of the Todd-AO layout giving the modern 5.1 channel allocation retained today by 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...
.
Ultra Stereo
By 1984, Dolby Stereo had a competitor. Ultra Stereo Labs had introduced a comparable stereo optical sound system, Ultra StereoUltra Stereo
Ultra Stereo is a cinematographic sound system that was developed by the year 1984Film Journal International August 1999, p. 34 in competition to the predominant format, Dolby Stereo, by former employees of that company. It is a 4/2/4 photographic sound encoding and decoding procedure that has the...
. Its cinema processor introduced improvements in matrix decoding, with greater channel separation. An included balancing circuit compensated for film weave and some imbalances between the left and right tracks that previously caused voice leakage into the surround channel. The Ultra Stereo sound system won a 1984 Technical Achievement Award from the Academy of Motion Picture Arts and Sciences.
Dolby Surround
Dolby Surround was the earliest consumer version of Dolby'sDolby Laboratories
Dolby Laboratories, Inc. , often shortened to Dolby Labs, is an American company specializing in audio noise reduction and audio encoding/compression.-History:...
multichannel analog film sound format Dolby Stereo.
Due to the compatibility of the Dolby Stereo matrix with mono and stereo playback, when films originally made in Dolby Stereo were released on stereo domestic video formats, such as VHS-HiFi or laserdisc, or broadcast on stereo TV the original two-channel Dolby Stereo soundtrack could be used. Some domestic listeners were keen to hear these soundtracks in a manner more akin to how they would have sounded in the theater and for that market some manufacturers produced simplified surround decoders. To keep the cost down these decoders dispensed with a center speaker output and the logic circuitry found on the professional decoder, but did include the surround delay. To distinguish these decoders from the professional units found in cinemas they were given the name "Dolby Surround" decoders. The term "Dolby Surround" was also licensed by Dolby for use on TV programs or straight-to-video movies recorded through the Dolby Stereo matrix.