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Stereophonic sound, commonly shortened to 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 of two (or stereo headphones) in such a way as to create the impression of sound heard from various directions, as in natural hearing.
Because the multi-dimensional perspective is the crucial aspect, the term stereophonic also applies to systems with more than two channels or speakers such as quadraphonic and surround sound. Binaural sound systems are also stereophonic.
Stereo sound has been in common use since the 1970s in entertainment media such as broadcast radio, recorded music, television, , cinema, computer audio, and the Internet.
Secondly artificial or pan stereo, in which a single-channel (monaural) sound is reproduced over multiple loudspeakers. By varying the relative amplitude of the signal sent to each speaker, an artificial direction (relative to the listener) can be suggested. The control that is used to vary this relative amplitude of the signal is known as a pan-pot (panoramic potentiometer). By combining multiple pan-potted mono signals, a complete, yet entirely artificial, sound field can be created.
In technical usage, means sound recording and sound reproduction that uses stereographic projection to encode the relative positions of objects and events recorded.
During two-channel stereo recording, two microphones are placed in strategically chosen locations relative to the sound source, with both recording simultaneously. The two recorded channels will be similar, but each will have distinct time-of-arrival and sound-pressure-level information. During playback, the listener's brain uses those subtle differences in timing and sound level to triangulate the positions of the recorded objects. Since each microphone records each wavefront at a slightly different time, the wavefronts are out of phase; as a result, constructive and destructive interference can occur if both tracks are played back on the same speaker. This phenomenon is known as phase cancellation. Coincident pair produce stereo recordings with minimal phase difference between channels.
This two-channel telephonic process was commercialized in France from 1890 to 1932 as the Théâtrophone, and in England from 1895 to 1925 as the Electrophone. Both were services available by coin-operated receivers at hotels and cafés, or by subscription to private homes."Court Circular", The Times (London), November 6, 1895, p. 7. "Post Office Electrical Engineers. The Electrophone Service", The Times (London), January 15, 1913, p. 24. "Wired Wireless", The Times (London), June 22, 1925, p. 8.
There have been cases in which two recording lathes (for the sake of producing two simultaneous masters) were fed from two separate microphones; when both masters survive, modern engineers have been able to synchronize them to produce stereo recordings from a time before intentional stereophonic recording technology existed. Elgar Remastered, Somm CD 261, and Accidental Stereo, Pristine Classical CD PASC422).
Blumlein began binaural experiments as early as 1933, and the first stereo discs were cut later the same year, twenty-five years before that method became the standard for stereo phonograph discs. These discs used the two walls of the groove at right angles in order to carry the two channels. In 1934, Blumlein recorded Mozart's Jupiter Symphony conducted by Sir Thomas Beecham at Abbey Road Studios in London using his vertical-lateral technique. Much of the development work on this system for cinematic use did not reach completion until 1935. In Blumlein's short test films (most notably, "Trains at Hayes Station", which lasts 5 minutes 11 seconds, and, "The Walking & Talking Film"), his original intent of having the sound follow the actor was fully realized.Robert Alexander (2013). "The Inventor of Stereo: The Life and Works of Alan Dower Blumlein". p. 83. CRC Press,
In the United States, Harvey Fletcher of Bell Laboratories was also investigating techniques for stereophonic recording and reproduction. One of the techniques investigated was the wall of sound, which used an enormous array of microphones hung in a line across the front of an orchestra. Up to 80 microphones were used, and each fed a corresponding loudspeaker, placed in an identical position, in a separate listening room. Several stereophonic test recordings, using two microphones connected to two styli cutting two separate grooves on the same wax disc, were made with Leopold Stokowski and the Philadelphia Orchestra at Philadelphia's Academy of Music in March 1932. The first (made on March 12, 1932), of Scriabin's , is the earliest known surviving intentional stereo recording. The performance was part of an all-Russian program including Mussorgsky's Pictures at an Exhibition in the Ravel orchestration, excerpts of which were also recorded in stereo. Stokowski, Harvey Fletcher, and the Bell Labs Experimental Recordings , stokowski.org, accessed March 1, 2012.
Bell Laboratories gave a demonstration of three-channel stereophonic sound on April 27, 1933, with a live transmission of the Philadelphia Orchestra from Philadelphia to Constitution Hall in Washington, D.C. over multiple Class A telephone lines. Leopold Stokowski, normally the orchestra's conductor, was present in Constitution Hall to control the sound mix. Five years later, the same system would be expanded onto multichannel film recording and used from the concert hall in Philadelphia to the recording labs at Bell Labs in New Jersey in order to record Walt Disney's Fantasia (1940) in what Disney called Fantasound.
Later that same year, Bell Labs also demonstrated binaural sound, at the Chicago World's Fair in 1933 using a dummy with microphones instead of ears.B.B. Bauer, "Some Techniques Toward Better Stereophonic Perspective", IEEE Transactions on Audio, May–June 1963, p. 89. The two were sent out over separate AM station bands." Radio Adds Third Dimension", Popular Science, Jan. 1953, p. 106.
The speakers produced sound levels of up to 100 decibels, and the demonstration held the audience "spellbound, and at times not a little terrified", according to one report."Sound Waves 'Rock' Carnegie Hall as 'Enhanced Music' is Played", The New York Times, April 10, 1940, p. 25. Sergei Rachmaninoff, who was present at the demonstration, commented that it was "marvellous" but "somehow unmusical because of the loudness." "Take that Pictures at an Exhibition", he said. "I didn't know what it was until they got well into the piece. Too much 'enhancing', too much Stokowski."
In the early 1940s, composer-conductor Alfred Newman directed the construction of a sound stage equipped for multichannel recording for 20th Century Fox studios. Several soundtracks from this era still exist in their multichannel elements, some of which have been released on DVD, including How Green Was My Valley, Anna and the King of Siam, The Day the Earth Stood Still and Sun Valley Serenade which, along with Orchestra Wives, feature the only stereophonic recordings of the Glenn Miller Orchestra as it was during its heyday of the Swing Era.
The Cinerama audio soundtrack technology, developed by Hazard E. Reeves, utilized seven discrete sound tracks on full-coat magnetic 35 mm film. The system featured five main channels behind the screen, two surround channels in the rear of the theater, plus a sync track to interlock the four machines, which were specially outfitted with aircraft servo-motors made by Ampex.
The advent of multitrack magnetic tape and film recording of this nature made high-fidelity synchronized multichannel recording more technically straightforward, though costly. By the early 1950s, all of the major studios were recording on 35 mm magnetic film for mixing purposes, and many of these so-called individual angles still survive, allowing for soundtracks to be remixed into stereo or even surround.
In April 1953, while This is Cinerama was still playing only in New York City, most moviegoing audiences heard stereophonic sound for the first time with House of Wax, an early 3-D film starring Vincent Price and produced by Warner Bros. Unlike the 4-track mag release-print stereo films of the period which featured four thin strips of magnetic material running down the length of the film, inside and outside the sprocket holes, the sound system developed for House of Wax, dubbed WarnerPhonic, was a combination of a 35 mm fully coated magnetic film that contained the audio tracks for left, center and right speakers, interlocked with the two dual-strip Polaroid system projectors, one of which carried a mono optical surround track and one that carried a mono backup track use in the event anything should go wrong.
Only two other films featured this unique hybrid WarnerPhonic sound: the 3-D production of The Charge at Feather River, and Island in the Sky. Unfortunately, as of 2012, the stereo magnetic tracks to both these films are considered lost forever. In addition, a large percentage of 3-D films carried variations on three-track magnetic sound: It Came from Outer Space; I, the Jury; The Stranger Wore a Gun; Inferno; Kiss Me, Kate; and many others.
VistaVision took a simplified, low-cost approach to stereophonic sound; its Perspecta system featured only a monaural track, but through subaudible tones, it could change the direction of the sound to come from the left, right or both directions at once.
Because of the standard 35 mm-size film, CinemaScope and its stereophonic sound was capable of being retrofitted into existing theaters. CinemaScope 55 was created by the same company in order to use a larger form of the system (55 mm instead of 35 mm) to allow for greater image clarity onscreen, and was supposed to have had 6-track stereo instead of four. However, because the film needed a new, specially designed projector, the system proved impractical, and the two films made in the process, Carousel and The King and I, were released in 35 mm CinemaScope reduction prints. To compensate, the premiere engagement of Carousel used a six-track magnetic full-coat in an interlock, and a 1961 re-release of The King and I, featured the film printed down to 70 mm with a six-channel soundtrack.
Eventually, 50 complete sets of combination 55/35 mm projectors and penthouse reproducers were completed and delivered by Century and Ampex, respectively, and 55 mm release print sound equipment was delivered by Western Electric. Several samples of 55 mm sound prints can be found in the Sponable Collection at the Film and Television Archives at Columbia University. The subsequently abandoned 55/35 mm Century projector eventually became the Century JJ 70/35MM projector.
Some films shot in 35 mm, such as Camelot, featured four-track stereophonic sound and were then blown up to 70 mm so that they could be shown on a giant screen with six-track stereophonic sound. Unfortunately however, many of these presentations were only pseudo stereo, utilizing a somewhat artificial six-track panning method. A process known somewhat derogatorily as the Columbia Spread was often used to synthesize Left Center and Right Center from a combination of Left and Center and Right and Center, respectively, or, for effects, the effect could be "panned" anywhere across the five stage speakers using a one-in/five-out pan pot. Dolby, who did not approve of this practice, which results in loss of separation, instead used the left center and right center channels for LFE (low-frequency enhancement) utilizing the bass units of the otherwise redundant intermediate front speakers, and later the unused HF capacity of these channels to provide for stereo surround in place of the mono surround.
At that time, AM radio had been around for roughly a decade, and broadcasters were looking for better materials from which to make phonograph records as well as a better format in which to record them to play over the narrow and thus inherently noisy radio channel. As radio had been playing the same shellac discs available to the public, it was found that, even though the playback system was now electric rather than acoustic, the surface noise on the disc would mask the music after just a few plays.
The development of acetate, bakelite, and vinyl, and the production of radio broadcast transcriptions helped to solve this. Once these considerably quieter compounds were developed, it was discovered that the rubber-idler-wheel-driven turntables of the period had a great deal of low-frequency rumble but only in the lateral plane. So, even though with all other factors being equal, the vertical plane of recording on disc had the higher fidelity, it was decided to record vertically to produce higher-fidelity recordings on these new materials, for two reasons, the increase in fidelity by avoiding the lateral rumble and to create incompatibility with home phonographs which, with their lateral-only playback systems, would only produce silence from a vertically modulated disc.
After RPM recording had been perfected for the movies in 1927, the speed of radio program transcriptions was reduced to match, once again to inhibit playback of the discs on normal home consumer equipment. Even though the stylus size remained the same as consumer records at either or , the disc size was increased from to the same as those used in early talking pictures in order to create further incompatibility. Now, not only could the records not be played on home equipment due to incompatible recording format and speed, they would not even fit on the player, which suited the copyright holders.
Another failed experiment in the late 1920s and early '30s involved recording the left channel on one side of the disc and recording the right channel on the other side of the disc. These were manufactured on twin film-company recording lathes which ran in perfect sync with one another, and were capable of counter-clockwise as well as conventional clockwise recording. Each master was run separately through the plating process, lined up to match, and subsequently mounted in a press. The dual-sided stereo disc was then played vertically, first in a system that featured two tonearms on the same post facing one another. The system had trouble keeping the two tonearms in their respective synchronous revolutions.
Five years later, Bell Labs was experimenting with a two-channel lateral-vertical system, where the left channel was recorded laterally and the right channel was recorded vertically, still utilizing a standard 3 mil 78 RPM groove, over three times larger than the modern LP stylus of the late 20th century. In this system all the low-frequency rumble was in the left channel and all the high-frequency distortion was in the right channel. Over a quarter of a century later, it was decided to tilt the recording head 45 degrees off to the right side so that both the low-frequency rumble and high-frequency distortion were shared equally by both channels, producing the 45/45 system we know today.
Each groove needed its own monophonic needle and cartridge on its own branch of the tonearm, and each needle was connected to a separate amplifier and speaker. This setup was intended to demonstrate Cook's cutter heads at a New York audio fair. It was not intended to promote the binaural process; but soon afterward, the demand for such recordings and the equipment to play them grew, and Cook's company, Cook Records, began to produce such records commercially. Cook recorded a vast array of sounds, ranging from railroad sounds to thunderstorms. By 1953, Cook had a catalog of about 25 stereo records for sale to ." Commercial Binaural Sound Not Far Off", Billboard, October 24, 1953, p. 15.
In the US, stereo magnetic tape recording was demonstrated on standard 1/4-inch tape for the first time in 1952, using two sets of recording and playback heads, upside-down and offset from one another." Adventures in Sound", Popular Mechanics, September 1952, p. 216. A year later, Remington Records began recording a number of its sessions in stereo, including performances by Thor Johnson and the Cincinnati Symphony Orchestra.
Later in 1952, more experimental stereo recordings were conducted with Leopold Stokowski and a group of New York studio musicians at RCA Victor Studios in New York City. In February 1954, the label also recorded a performance of Berlioz' masterpiece The Damnation of Faust by the Boston Symphony Orchestra under the direction of Charles Munch, the success of which led to the practice of regularly recording sessions in stereo.
Shortly afterward, RCA Victor recorded the last two NBC Blue Network broadcast concerts by famed conductor Arturo Toscanini and the NBC Symphony Orchestra, on stereophonic magnetic tape, however, they were never officially released, though they have long been available on pirated LPs and CDs. In the UK, Decca Records began recording sessions in stereo in mid-1954, and by that time even smaller labels in the US such as Concertapes, Bel Canto and Westminster along with major labels such as RCA Victor began releasing stereophonic recordings on two-track prerecorded reel-to-reel magnetic tape, priced at twice or three times the cost of monaural recordings, which retailed for around $2.95 to $3.95 apiece for a standard monaural LP. Even two-track monaural tape which had to be flipped over halfway through and carried exactly the same information as the monaural LP but without the crackles and pops were being sold for $6.95.
Stereophonic sound came to at least a select few living rooms of the mid-1950s."Hi-Fi: Two-Channel Commotion", The New York Times, November 17, 1957, p. XX1.
Also in December 1957, Bel Canto Records, another small label, produced its own stereophonic demonstration disc on multicolored vinyl so that stereo dealers would have more than one choice for demonstration. With the supplied special turntables featuring a clear platter lighted from underneath to show off the color as well as the sound, the stunt worked even better for Bel Canto, whose roster of jazz, easy listening and lounge music, pressed onto their trademark Caribbean-blue vinyl sold well throughout 1958 and early into 1959.
When Audio Fidelity released its stereophonic demonstration disc, there was no affordable magnetic cartridge on the market capable of playing it. After the release of other demonstration discs and the respective libraries from which they were culled, the other spur to the popularity of stereo discs was the reduction in price of a stereo cartridge, for playing the discs–from $250 to $29.95 in June 1958." Audio Fidelity Bombshell Had Industry Agog", Billboard, December 22, 1962, p. 36. The first four mass-produced stereophonic discs available to the buying public were released in March 1958 Johnny Puleo and his Harmonica Gang Volume 1 (AFSD 5830), Railroad – Sounds of a Vanishing Era (AFSD 5843), Lionel – Lionel Hampton and his Orchestra (AFSD 5849) and Marching Along with the Dukes of Dixieland Volume 3 (AFSD 5851). By the end of March, the company had four more stereo LPs available, interspersed with several Bel Canto releases." CBS Discloses Stereo Step," Billboard, March 31, 1958, p. 9.
Although both monaural as well as stereo LP records were manufactured for the first ten years of stereo on disc, the major record labels issued their last monaural albums in 1968, relegating the format to 45 RPM singles, and radio promotional materials which continued until 1975.Sylvan Fox, "Disks Today: New Sounds and Technology Spin Long-Playing Record of Prosperity", The New York Times, August 28, 1967, p. 35. RCA Victor Red Seal Labelography (1950–1967)." Mfrs. Strangle Monaural ", Billboard, January 6, 1968, p. 1.
In 1925 it was reported that additional experimental stereo transmissions had been conducted in Berlin, again with two mediumwave transmissions. "Radio Stereophony" by Ludwig Kapeller, Radio News, October 1925, pages 416, 544–546. The transmitting wavelengths of 430 and 505 meters correspond to approximately 698 and 594 kHz respectively. In December of that year the BBC's long wave station, 5XX in Daventry, Northamptonshire, participated in the first British stereo broadcast a concert from Manchester, conducted by Hamilton Harty with 5XX transmitting nationally the right channel, and local BBC stations broadcasting the left channel on mediumwave. "Stereoscopic Broadcasting" by Captain H. J. Round, Wireless, September 26, 1925, pages 55–56. The BBC repeated the experiment in 1926, using 2LO in London and 5XX at Daventry. On June 12, 1946, a similar experimental broadcast using two stations was conducted in Holland, which was mistakenly thought to be the first in Europe and possibly the world. "Dutch Regard 'Stereophonic Broadcasting' Experiment as Significant for Future", , Foreign Commerce Weekly, August 24, 1946, page 16.
1952 saw a renewed interest in the United States in stereo broadcasting, still using two stations for the two channels, in part in reaction to the development of two-channel tape recordings. The Federal Communications Commission's (FCC) duopoly rule limited station owners to one AM station per market. But many station owners now had access to a co-owned FM station, and most of these tests paired AM and FM stations. On May 18 KOMO and KOMO-FM in Seattle, Washington conducted an experimental broadcast, "KOMO Binaural" Broadcasting, June 2, 1952, page 46. and four days later Chicago AM radio station WGN and its sister FM station, WGNB, collaborated on an hourlong stereophonic demonstration. "Binaural Feature at Parts Show", Broadcasting, May 26, 1952, page 73. On October 23, 1952, two Washington, D.C. FM stations, WTOP-FM and WASH, conducted their own demonstration. "2 Stations, 2 Mikes, 2 Radios Give Broadcast Realistic Sound" , Washington (D.C.) Evening Star, October 24, 1952, page A-24. Later that month New York City's WQXR, paired with WQXR-FM, initiated its first stereophonic broadcast, which was relayed to WDRC and WHCN."Two WDRC Stations Will Present 'Binaural' System Demonstrations", Hartford Courant, October 29, 1952, page 26. "WDRC" (advertisement), Broadcasting, December 8, 1952, page 9. By 1954, WQXR was broadcasting all of its live musical programs in stereophonic sound, using its AM and FM stations for the two audio channels.Multiple sources:
Rensselaer Polytechnic Institute began a weekly series of live stereophonic broadcasts in November 1952 using two AM stations, WHAZ in conjunction with a very low-powered local carrier current station, which meant the stereo listening area did not extend beyond the college campus. "Binaural Music on the Campus", , Popular Science, April 1953, p. 20.
The revived dual transmitter tests were of limited success, because they still required two receivers, and with AM-FM pairings the sound quality of the AM transmissions was generally significantly inferior to the FM signals.
It was eventually determined that the bandwidth assigned to individual FM stations was sufficient to support stereo transmissions from a single transmitter. In the United States, the FCC oversaw comparison tests, conducted by the National Stereophonic Radio Committee, of six proposed FM standards. These tests were conducted by WLTJ in Pittsburgh, Pennsylvania during July and August 1960. In April 1961 the FCC adopted stereophonic FM technical standards, largely based on a Zenith-General Electric proposal, with licensed regular stereophonic FM radio broadcasting set to begin in the United States on June 1, 1961. "Finally, FCC Okays Stereo", Broadcasting, April 24, 1961, pages 65–66. At midnight in their respective time zones on June 1, General Electric's WRVE in Schenectady, New York, Zenith's WUSN in Chicago, and KMLA in Los Angeles became the first three stations to begin broadcasting using the new stereo standards. "Three fms meet date for multiplex stereo", Broadcasting, June 5, 1961, page 58.
Following experimental FM stereo transmissions in the London area in 1958 and regular Saturday morning demonstration transmissions using TV sound and medium wave (AM) radio to provide the two channels, the first regular BBC transmissions using an FM stereo signal began on the BBC Third Programme network on August 28, 1962. Start of experimental stereo broadcasting 28 August 1962 , BBC
In Sweden, Televerket invented a different stereo broadcasting system called the Compander System. It had a high level of channel separation and could even be used to broadcast two separate mono signals for example for language studies (with two languages at the same time). But tuners and receivers with the pilot-tone system were sold so people in southern Sweden could listen to, for example, Danish radio. At last Sweden (the Televerket) decided to start broadcasting in stereo according to the pilot-tone system in 1977.
After the advent of FM stereo broadcasts in 1962, a small number of music-oriented TV shows were broadcast with stereo sound using a process called , in which the audio portion of the show was carried over a local FM stereo station.For example: Jack Gould, "TV: Happy Marriage With FM Stereo", The New York Times, December 26, 1967, p. 67. In the 1960s and 1970s, these shows were usually manually synchronized with a reel-to-reel tape recording mailed to the FM station (unless the concert or music originated locally). In the 1980s, satellite delivery of both television and radio programs made this fairly tedious process of synchronization unnecessary. One of the last of these simulcast programs was Friday Night Videos on NBC.
The BBC made extensive use of simulcasting between 1974 and around 1990. The first such transmission was in 1974 when the BBC broadcast a recording of Van Morrison's London Rainbow Concert simultaneously on BBC2 TV and Radio 2. After that it was used for many other music programs, live and recorded, including the annual BBC The Proms and the Eurovision Song Contest. The advent of NICAM stereo sound with TV rendered this unnecessary.
Cable TV systems used simulcasting to deliver stereo programs for many years. One of the first stereo cable stations was The Movie Channel, though the most popular cable TV station that drove up the usage of stereo simulcasting was MTV.
Japanese television began stereo broadcasts in 1978,"/ "Japan's Stereo TV System", , The New York Times, June 16, 1984. and regular transmissions with stereo sound came in 1982. "1982". Chronomedia. . By 1984, about 12% of the programming, or about 14 or 15 hours per station per week were broadcast in stereo. West Germany's second television network, ZDF, began offering stereo programs in 1984.
In 1979, The New York Times reported, "What has prompted the television industry to embark on establishing high-fidelity sound standards now, according to engineering executives involved in the project, is chiefly the rapid march of the new television technologies, especially those that are challenging broadcast television, such as the Laserdisc."Les Brown, "Hi-fi Stereo TV Coming in 2 to 4 Years", The New York Times, October 25, 1979, p. C-18.
For analog TV (PAL and NTSC), various modulation schemes are used in different parts of the world to broadcast more than one sound channel. These are sometimes used to provide two mono sound channels that are in different languages, rather than stereo. Multichannel television sound is used mainly in the Americas. NICAM is widely used in Europe, except in Germany, where Zweikanalton is used. The EIAJ FM/FM subcarrier system is used in Japan. For digital TV, MP2 audio streams are widely used within MPEG-2 program streams. Dolby Digital is the audio standard used for digital TV in North America, with the capability for anywhere between 1 and 6 discrete channels.
Multichannel Television Sound (MTS) is the method of encoding three additional into an NTSC-format audio carrier wave. It was adopted by the FCC as the United States standard for stereo television transmission in 1984. Sporadic network transmission of stereo audio began on NBC on July 26, 1984, with The Tonight Show Starring Johnny Carson although at the time, only the network's New York City flagship station, WNBC-TV, had stereo broadcast capability.Peter W. Kaplan, "TV Notes", New York Times, July 28, 1984, sec. 1, p. 46. Regular stereo transmission of programs began in 1985. ABC and CBS followed suit in 1986 and 1987.
This technique can produce phase issues when the stereo signal is mixed to mono.
The left and right channels are produced through a simple matrix: left = mid + side; right = mid − side (the polarity-reversed side signal). This configuration produces a completely mono-compatible signal and, if the mid and side signals are recorded (rather than the matrixed left and right), the stereo width can be manipulated after the recording has taken place. This makes it especially useful for film-based projects.
| A is a square wave and B is one thrice the frequency. |
| Different amounts of A and B are mixed into the and channels. |
| To widen the stereo effect, a fraction of the opposing channel is subtracted from each channel. |
| Normalized results show the signals A and B partly separated. |
In the course of restoration or remastering of monophonic records, various techniques of pseudo-stereo, quasi-stereo, or rechanneled stereo have been used to create the impression that the sound was originally recorded in stereo. These techniques first involved hardware methods (see Duophonic) or, more recently, a combination of hardware and software. Multitrack Studio, from Bremmers Audio Design (The Netherlands), uses special filters to achieve a pseudo-stereo effect: the shelve filter directs low frequencies to the left channel and high frequencies to the right channel, and the comb filter adds a small delay in signal timing between the two channels, a delay barely noticeable by ear,The comb filter allows range of manipulation between 0 and 100 milliseconds. but contributing to an effect of widening original flattiness of mono recording. A Review and an Extension of Pseudo-Stereo...
The special pseudo-stereo circuit invented by Kishii and Noro, from Japan was patented in the United States in 2003, with already previously issued patents for similar devices. Artificial stereo techniques have been used to improve the listening experience of monophonic recordings or to make them more "saleable" in today's market, where people expect stereo. Some critics have expressed concern about the use of these methods.
Numerous early two-track-stereo reel-to-reel tapes as well as several experimental stereo disc formats of the early 1950s branded themselves as binaural, however they were merely different incarnations of the above-described stereo or two-track mono recording methods (lead vocal or instrument isolated on one channel and orchestra on the other sans lead.)
Descriptions of stereophonic sound tend to stress the ability to localize the position of each instrument in space, but this would only be true in a carefully engineered and installed system, where speaker placement and room acoustics are taken into account. In reality, many playback systems, such as all-in-one boombox units and the like, are incapable of recreating a realistic stereo image. Originally, in the late 1950s and 1960s, stereophonic sound was marketed as seeming "richer" or "fuller-sounding" than monophonic sound, but these sorts of claims were and are highly subjective, and again, dependent on the equipment used to reproduce the sound. In fact, poorly recorded or reproduced stereophonic sound can sound far worse than well-done monophonic sound. Nevertheless, many record companies released stereo "demonstration" records to help promote stereo. These records often included instructions for setting up a stereo system, 'balancing' the speakers, and a variety of ambient recordings to show off the stereo effect. When playing back stereo recordings, the best results are obtained by using two identical speakers, in front of and equidistant from the listener, with the listener located on a center line between the two speakers. In effect, an equilateral triangle is formed, with the angle between the two speakers around 60 degrees as seen from the listener's point of view. Many higher quality multichannel (two-channel and beyond) speaker systems, then and now, include detailed instructions specifying the ideal angles and distances between the speakers and the listening position to maximize the effect based on, often extensive, testing of the particular system's design.
In the Westrex system, each channel drives the cutting head at a 45-degree angle to the vertical. During playback, the combined signal is sensed by a left-channel coil mounted diagonally opposite the inner side of the groove and a right-channel coil mounted diagonally opposite the outer side of the groove. The Westrex system provided for the polarity of one channel to be inverted: this way large groove displacement would occur in the horizontal plane and not in the vertical one. The latter would require large up-and-down excursions and would encourage cartridge skipping during loud passages.
The combined stylus motion is, in terms of the vector, the sum and difference of the two stereo channels. Effectively, all horizontal stylus motion conveys the L+R sum signal, and vertical stylus motion carries the L−R difference signal. The advantages of the 45/45 system are that it has greater compatibility with monophonic recording and playback systems.
Even though a monophonic cartridge will technically reproduce an equal blend of the left and right channels, instead of reproducing only one channel, this was not recommended in the early days of stereo due to the larger stylus ( vs. for stereo) coupled with the lack of vertical compliance of the mono cartridges available in the first ten years of stereo. These factors would result in the stylus 'digging into' the stereo vinyl and carving up the stereo portion of the groove, destroying it for subsequent playback on stereo cartridges. This is why one often notices the banner "PLAY ONLY WITH STEREO CARTRIDGE AND STYLUS" on stereo vinyl issued between 1958 and 1964.
Conversely, and with the benefit of no damage to any type of disc even from the beginning, a stereo cartridge reproduces the lateral grooves of monophonic recording equally through both channels, rather than through one channel. Also, it gives a more balanced sound, because the two channels have equal fidelity as opposed to providing one higher-fidelity laterally recorded channel and one lower-fidelity vertically recorded channel. Overall, this approach may give higher fidelity, because the difference signal is usually of low power, and is thus less affected by the intrinsic distortion of hill and dale-style recording.
Additionally, surface noise tends to be picked up in a greater capacity in the vertical channel, therefore a mono record played on a stereo system can be in worse shape than the same record in stereo and still be enjoyable. (See Gramophone record for more on lateral and vertical recording.)
Although this system was conceived by Alan Blumlein of EMI in 1931 and was patented in the UK the same year, it was not reduced to practice by the inventor as was a requirement for patenting in the US and elsewhere at that time. (Blumlein was killed in a plane crash while testing radar equipment during WW-II, and he, therefore, never reduced the system to actual practice through both a recording and a reproducing means.) EMI cut the first stereo test discs using this system in 1933, but it was not applied commercially until a quarter of a century later, and by another company entirely (Westrex division of Litton Industries Inc, as the successor to Western Electric Company), and dubbed StereoDisk. Stereo sound provides a more natural listening experience, since the spatial location of the source of a sound is (at least in part) reproduced.
In the 1960s, it was common practice to generate stereo versions of music from monophonic master tapes, which were normally marked "electronically reprocessed" or "electronically enhanced" stereo on track listings. These were generated by a variety of processing techniques to try to separate out various elements; this left noticeable and unsatisfactory artifacts in the sound, typically sounding "phasey". However, as multichannel recording became increasingly available, it has become progressively easier to master or remaster more plausible stereo recordings out of the archived multitrack master tapes.
Most multichannel recordings are stereo recordings only in the sense that they are stereo "mixes" consisting of a collection of mono and/or true stereo recordings. Modern popular music, in particular, is usually recorded using close miking techniques, which artificially separate signals into several tracks. The individual tracks (of which there may be hundreds) are then "mixed down" into a two-channel recording. The audio engineers determine where each track will be placed in the stereo "image", by using various techniques that may vary from very simple (such as "left-right" panning controls) to more sophisticated and extensively based on psychoacoustic research (such as channel equalization, , and the use of delay to exploit the precedence effect). The end product using this process often bears little or no resemblance to the actual physical and spatial relationship of the musicians at the time of the original performance; indeed, it is not uncommon for different tracks of the same song to be recorded at different times (and even in different studios) and then mixed into a final two-channel recording for commercial release.
Classical music recordings are a notable exception. They are more likely to be recorded without having tracks dubbed in later as in pop recordings, so that the actual physical and spatial relationship of the musicians at the time of the original performance can be preserved on the recording.
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