Stereophonic sound

Stereophonic sound or, more commonly, stereo,
is a method of sound reproduction that creates an illusion of directionality and audible
perspective. This is usually achieved by using two or more independent audio channels through
a configuration of two or more loudspeakers in such a way as to create the impression
of sound heard from various directions, as in natural hearing. Thus the term “stereophonic”
applies to so-called “quadraphonic” and “surround-sound” systems as well as the more common two-channel,
two-speaker systems. It is often contrasted with monophonic, or “mono” sound, where audio
is in the form of one channel, often centered in the sound field. Stereo sound is now common
in entertainment systems such as broadcast radio and TV, recorded music and the cinema.
The word stereophonic derives from the Greek “στερεός”, “firm, solid” + “φωνή”,
“sound, tone, voice” and it was coined in 1927 by Western Electric, by analogy with
the word “stereoscopic”. Description
Stereo sound systems can be divided into two forms: The first is “true” or “natural” stereo
in which a live sound is captured, with any natural reverberation or ambience present,
by an array of microphones. The signal is then reproduced over multiple loudspeakers
to recreate, as closely as possible, the live sound.
Secondly “artificial” or “pan-pot” stereo, in which a single-channel sound is reproduced
over multiple loudspeakers. By varying the relative amplitude of the signal sent to each
speaker an artificial direction can be suggested. The control which is used to vary this relative
amplitude of the signal is known as a “pan-pot”. By combining multiple “pan-potted” mono signals
together, a complete, yet entirely artificial, sound field can be created.
In technical usage, true stereo 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. Stereo recordings often
cannot be played on monaural systems without a significant loss of fidelity. 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.
History Early work Clément Ader demonstrated the first two-channel
audio system in Paris in 1881, with a series of telephone transmitters connected from the
stage of the Paris Opera to a suite of rooms at the Paris Electrical Exhibition, where
listeners could hear a live transmission of performances through receivers for each ear.
Scientific American reported, “Every one who has been fortunate enough to
hear the telephones at the Palais de l’Industrie has remarked that, in listening with both
ears at the two telephones, the sound takes a special character of relief and localization
which a single receiver cannot produce… This phenomenon is very curious, it approximates
to the theory of binauricular audition, and has never been applied, we believe, before
to produce this remarkable illusion to which may almost be given the name of auditive perspective.”
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.
Modern stereophonic sound Modern stereophonic technology was invented
in the 1930s by British engineer Alan Blumlein at EMI, who patented stereo records, stereo
films, and also surround sound. In early 1931, Blumlein and his wife were
at a local cinema. The sound reproduction systems of the early “talkies” invariably
only had a single set of speakers – which could lead to the somewhat disconcerting effect
of the actor being on one side of the screen whilst his voice appeared to come from the
other. Blumlein declared to his wife that he had found a way to make the sound follow
the actor across the screen. The genesis of these ideas is uncertain, but
he explained them to Isaac Shoenberg in the late summer of 1931. His earliest notes on
the subject are dated 25 September 1931, and his patent had the title “Improvements in
and relating to Sound-transmission, Sound-recording and Sound-reproducing Systems”. The application
was dated 14 December 1931, and was accepted on 14 June 1933 as UK patent number 394,325.
Whereas work led by Harvey Fletcher at Bell Labs at about the same time considered sound
systems using multiple channels, Blumlein always aimed at a system with just two channels.
The patent covered many ideas in stereo, some of which are used today and some not. Some
70 claims include: A “shuffling” circuit, which aimed to preserve
the directional effect when sound from a spaced pair of microphones was reproduced via stereo
headphones instead of a pair of loudspeakers; The use of a coincident pair of velocity microphones
with their axes at right angles to each other, which is still known as a “Blumlein Pair”;
Recording two channels in the single groove of a record using the two groove walls at
right angles to each other and 45 degrees to the vertical;
A stereo disc-cutting head; Using hybrid transformers to matrix between
left and right signals and sum and difference signals;
He 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. Much of the development work on this system
for cinematic use did not reach completion until 1935. In a few short test films, Blumlein’s
original intent of having the sound follow the actor was fully realised.
In 1934, Blumlein recorded Mozart’s Jupiter Symphony conducted by Sir Thomas Beecham at
the Abbey Road Studio using his vertical-lateral technique.
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, of Scriabin’s Prometheus: Poem
of Fire, is the earliest known surviving intentional stereo recording.
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 exapanded onto multi-channel
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 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, . The two signals were sent out over
separate AM station bands. Carnegie Hall demonstration
Utilizing selections recorded by the Philadelphia Orchestra, under the direction of Leopold
Stokowski, intended for but not used in Walt Disney’s Fantasia, the Carnegie Hall demonstration
by Bell Laboratories on April 9 and 10, 1940, used three huge speaker systems. Synchronization
was achieved by making the recordings in the form of three motion picture soundtracks recorded
on a single piece of film with a fourth track being used to regulate volume expansion.
This was necessary due to the limitations of dynamic range on optical motion picture
film of the period, however the volume compression and expansion were not fully automatic, but
were designed to allow manual studio “enhancement”; i.e., the artistic adjustment of overall volume
and the relative volume of each track in relation to the others. Stokowski, who was always interested
in sound reproduction technology personally participated in the “enhancement” of the sound
at the demonstration. 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. 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.”
Motion picture era In 1937, Bell Laboratories in New York City
gave a demonstration of two-channel stereophonic motion pictures, developed by Bell Labs and
Electrical Research Products, Inc. Once again, conductor Leopold Stokowski was on hand to
try out the new technology, recording onto a special proprietary nine-track sound system
at the Academy of Music in Philadelphia, during the making of the movie One Hundred Men and
a Girl for Universal Pictures in 1937, after which the tracks were mixed down to one for
the final soundtrack. A year later, MGM started using three tracks instead of one to record
the musical selections of movie soundtracks, and very quickly upgraded to four. One track
was used for dialogue, two for music, and one for sound effects. The purpose for this
form of multitrack recording was to make mixing down to a single optical track easier and
was not intended to be a recording for stereophonic purposes. The very first two-track recording
MGM made was “It Never Rains But What It Pours” by Judy Garland, recorded on June 21, 1938,
for the movie Love Finds Andy Hardy. Fantasound
Walt Disney began experimenting with multi-channel sound in the early 1930s as noted above. The
first commercial motion picture to be exhibited with stereophonic sound was Walt Disney’s
Fantasia, released in November 1940, for which a specialized sound process was developed.
As in the Carnegie Hall demonstrations six months earlier, Fantasound used a separate
film containing four optical sound tracks. Three of the tracks were used to carry left,
center and right audio, while the fourth track carried three tones which individually controlled
the volume level of the other three. The film was not a financial success, however, and
after two months of road-show exhibition in selected cities, its soundtrack was remixed
into mono sound for general release. It was not until its 1956 re-release that stereo
sound was restored to the film. 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 advent of multi-track magnetic tape and
film recording made high fidelity synchronized multichannel recording more technically straightforward,
though costly. By the early 1950s, all of the major studios were recording on 35mm 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.
Cinerama Motion picture theatres, however, are where
the real introduction of stereophonic sound to the public occurred. Amid great fanfare,
Stereo sound was officially proven commercially viable by the public on September 30, 1952
with the release of a Cinerama demonstration film entitled This is Cinerama. The format
was a then-spectacular widescreen process featuring three separate motion picture films
running in synchronization with one another, adding one film panel each to the viewer’s
left and right in addition to the usual front and center, creating a truly immersive panoramic
visual experience, comparable in some ways to today’s IMAX.
Similarly, the audio soundtrack technology, developed by Hazard E. Reeves, a pioneer in
magnetic recording, utilized seven discrete magnetic sound tracks in order to envelop
the theatregoer in an aural experience just as spectacular as that playing on the screen:
five behind the screen, plus two surround channels.
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 35MM fully coated magnetic
film that contained the audio tracks for Left-Center-Right, 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, should anything go wrong. Only two other films featured this strange
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. Widescreen
Inspired by Cinerama, the movie industry moved quickly to create simpler and cheaper widescreen
systems, such as Warner Bros. Panavision, Paramount Pictures’ VistaVision and Twentieth
Century-Fox Film Corporation’s CinemaScope, the latter of which used up to four separate
magnetic sound tracks. 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 to allow for greater image clarity onscreen, and was supposed to have had 6-track
stereo instead of four as Super Panavision 70 would have over a decade later. 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, used a six-track stereo soundtrack as well.
However, 50 complete sets of combination 55/35 mm projectors and “penthouse” reproducers were
eventually completed and delivered by Century and Ampex, respectively, and 55 mm release
print sounding 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. Todd-AO
After this disappointing experience with a proprietary “wide gauge” system, Fox purchased
the Todd-AO system and re-engineered it into a more modern 24 fps system with brand-new
65MM self-blimped production cameras and brand-new 65MM MOS cameras and brand-new Super Baltar
lenses in a wide variety of focal lengths, first employed on South Pacific. Essentially,
although Todd-AO was also available to others, the format became Fox’s premier origination
and presentation apparatus, replacing CinemaScope 55. Current DVDs of the two CinemaScope 55
feature titles were transferred from the original 55mm negatives, often including the separate
35MM films as extras for comparison. Back to mono
However, beginning in 1957, films recorded in stereo carried an alternate mono track
for theatres not ready or willing to re-equip for stereo. From then until about 1975, when
Dolby Stereo was used for the first time in films, most motion pictures—even some from
which stereophonic soundtrack albums were made, such as Zeffirelli’s Romeo and Juliet—were
still released in monaural sound, stereo being reserved almost exclusively for expensive
musicals such as West Side Story, My Fair Lady, or Camelot; epics such as Ben-Hur or
Cleopatra;. Stereo was also reserved for dramas with a strong reliance on sound effects or
music, such as Rosemary’s Baby or The Graduate, with its Simon and Garfunkel score.
Dolby Stereo Today, virtually all films are released in
stereophonic sound as the Westrex Stereo Variable-Area system developed in 1977 for Star Wars is
no more expensive to manufacture than mono. The format employs the same Western ElectricNuoptix
RA-1231 recorder, and coupled with QS quadraphonic matrixing technology licensed to Dolby Labs
from Sansui, this SVA system can produce the same Left, Center, Right and Surround sound
of the original CinemaScope system of 1953 by using a single standard width optical track.
This important development finally brought stereo sound to so-called Flat films presented
at the most common aspect ratio of 1.85:1 although a number of `flat’ films are photographed
and presented at a ratio of 1.66:1, common in Europe or 1.75:1 common in museums.
Producers often took advantage of the six magnetic soundtracks available for 70mm film
release prints, and productions shot in either 65MM or to save money, in 35MM and then blown
up to 70MM. In these instances, the 70MM prints would be mixed for stereo, while the 35MMreduction
prints would be remixed for mono. Some films shot in 35MM, such as Camelot,
featured four-track stereophonic sound and were then “blown-up” to 70MM 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 Stereo was succeeded by Dolby Digital 5.1 in the cinema and more recently with the
introduction of digital cinema, Dolby Surround 7.1 and Dolby Atmos in 2010 and 2012 respectively.
Modern home audio and video From 1940 to 1970, the progress of stereophonic
sound was paced by the technical difficulties of recording and reproducing two or more channels
in synchronization with one another and by the economic and marketing issues of introducing
new audio media and equipment. A stereo system cost roughly twice as much as a monophonic
system, since a stereo system had to be assembled by the user after purchasing two preamplifiers,
two amplifiers, and two speaker systems in addition to purchasing a twin-tuner radio,
upgrading his tape recorder to a stereo model and having his phonograph fitted with a stereo
cartridge. In the early days it was not clear whether consumers would think the sound was
so much better as to be worth twice the price. Stereo experiments on disc
Early lateral, vertical and double-sided stereo Edison had been recording in a hill-and-dale
or vertically modulated format on his cylinders and discs since 1877, and Berliner had been
recording in a side-to-side or lateral format since shortly thereafter. Each format developed
onto its own trajectory until the late 1920s when electric recording on disc, utilizing
a microphone surpassed acoustic recording where the performer needed to shout or play
very loudly into what basically amounted to a megaphone in reverse.
At that time, AM radio had been around for roughly a decade, and broadcasters were looking
for both 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 shellacque 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.
Enter Acetate Bakelite and Vinyl and Radio Broadcast Transcriptions. Once these considerably
more quiet 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 lateral plane of
recording on disc had the higher fidelity, it was decided to record vertically to produce
higher-fidelity recordings on these new `silent-surface’ materials, for two reasons, the increase in
fidelity and the incompatibility with home phonographs which, with their lateral-only
playback systems would only produce silence from a vertically modulated disc.
After 33-1/3 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 3 mils or 2.7 mils, the disc size was increased from 12-inches to
the same 16-inches as those used in early talking pictures in order to inhibit the practice
even further. Now, not only could the records not be played on home equipment due to incompatible
recording format and speed, they wouldn’t even fit on the player either, which suited
the copyright holders just fine. Two-channel high fidelity and other experiments
During the same period engineers got a bright idea. Split the signal into two parts, bass
and treble, and record the treble on its own track near the edge of the disc in a lateral
format so that there would be no high-frequency distortion, and then record the bass on its
own track in a vertical fashion to get rid of the rumble. Unfortunately, vertical grooves
take up more space than lateral grooves; so when the bass track was full, starting halfway
through the disc and ending up at the center, the treble track had a large amount of unused
space at the end. The alternative was to record it at a wider pitch i.e. lines-per-inch in
order to match up with the bass track and keep both styli in the same place, limiting
the playing time to slightly longer than a single even at 33-1/3 RPM on a 12-inch disc.
Another failed experiment in the late 1920s and early ’30s involved recording the left
channel on the left side of the disc and recording the right channel on the right side of the
disc. These were manufactured on twin film-company recording lathes which ran in perfect sync
with one another with no variation, and were capable of not only outside-in as well as
inside-out recordings but also counter-clockwise as well as conventional clockwise recording
by mounting the cutting head wrong-way-out with a special adapter. One master was recorded
conventionally and the other was recorded counterclockwise, each master was run separately
through the plating process, lined up to match, and subsequently mounted in a press. This
recording method was later used to record counter-clockwise discs by Mattel for one
of its answers to the GAF Talking View Master in the mid-60s.
The dual-sided stereo disc was then played vertically, first in a system that featured
two tonearms on the same post facing one another, and later on in an offset system where one
tonearm was placed conventionally and the other tonearm was placed opposite, i.e. not
only on the other side of the mechanism, but facing the other way as well so that both
tonearms could start at the edge and play to the center. But, even with playing the
disc vertically in a rotating clamp, the same trouble was observed with keeping the two
tonearms in their respective synchronous revolutions. The system was developed further however and
adapted so that a single tonearm could play one side of a record or the other in jukeboxes
of the late 1930s and early ’40s. 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. The trouble
with that was, once again, 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. Emory Cook
In 1952, Emory Cook, who already had become famous by designing new feedback disk-cutter
heads to improve sound from tape to vinyl, took the two-channel high-fidelity system
described above and developed a somewhat misnamed “binaural” record out of it, which consisted
of the same two separate channels cut into two separate groups of grooves running next
to each other as described above, i.e. one running from the edge of the disc to halfway
through and the other starting at the halfway point and ending up towards the label, but
he used two lateral grooves with a 500 Hz crossover in the inner track to try and compensate
for the lower fidelity and high frequency distortion on the inner track.
Each groove needed its own monophonic needle and cartridge on its own branch of tonearm,
and each needle was connected to a separate amplifier and speaker. This setup was intended
to give a demonstration at a New York audio fair of Cook’s cutter heads rather than to
sell the record; but soon afterward, the demand for such recordings and the equipment to play
it grew, and 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 audiophiles.
Magnetic tape recording 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. 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 that same year, 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 Münch, the success of which led to the practice of regularly recording
sessions in stereo. Shortly afterwards, the last two public concerts
directed by famed conductor Arturo Toscanini were recorded on stereophonic magnetic tape,
however they were not released as such until 1987 and 2007, respectively. In the UK, Decca
Records began recording sessions in stereo in mid-1954, and by that time even smaller
labels in the U.S. 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.
One has to understand that, in the United States, the average working man in 1954 might
be taking home $50–$60 a week if he was lucky and paying $75–$100 a month in rent
for his two-room apartment. Therefore the price of a great deal of two-track stereo
tape recordings of the period being upwards of $12.95-$18.95 apiece for a full-length
album when the corresponding mono LP was only $3.95, would be prohibitive. In addition,
the cost of the stereophonic recorder upon which to play them may have been equal to
or greater than the cost of a new car. However, audiophiles, with little or no regard
for the cost, bought them and the players anyway, and stereophonic sound came to at
least a select few living rooms of the mid-1950s. Stereo recording became widespread in the
music business by the 3rd quarter of 1957. Stereo on disc In November 1957, the small Audio Fidelity
Records label released the first mass-produced stereophonic disc. Sidney Frey, founder and
president, had Westrex engineers, owners of one of the two rival stereo disk-cutting systems,
cut a disk for release before any of the major record labels could do so. Side 1 featured
the Dukes of Dixieland, and Side 2 featured railroad and other sound effects designed
to engage and envelop the listener. This demonstration disc was introduced to the public on December
13, 1957 at the Times Auditorium in New York City. Only 500 copies of this initial demonstration
record were pressed and three days later, Frey advertised in Billboard Magazine that
he would send a free copy to anyone in the industry who wrote to him on company letterhead.
The move generated such a great deal of publicity that early stereo phonograph dealers were
forced to demonstrate on Audio Fidelity Records. 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. Affordable cartridges
After the release of the 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 magnetic cartridge, for playing the disks, from $250 to $29.95 in June 1958.
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, Railroad –
Sounds of a Vanishing Era, Lionel – Lionel Hampton and his Orchestra and Marching Along
with the Dukes of Dixieland Volume 3. By the end of March, the company had four more stereo
LPs available, interspersed with several Bel Canto releases.
Although both monaural as well as stereo LP records were manufactured for the first ten
years of stereo on disc, the major record labels stopped making monaural albums after
1968, relegating the format to 45 RPM singles, flexidiscs and radio promotional materials
which continued on through the end of 1974. Early broadcasting
Radio: In December 1925, the BBC’s experimental transmitting station, 5XX, in Daventry, Northamptonshire,
made radio’s first stereo broadcast—a concert from Manchester, conducted by Sir Hamilton
Harty—with 5XX broadcasting the right channel nationally by long wave and local BBC stations
broadcasting the left channel by medium wave. The BBC repeated the experiment in 1926, using
2LO in London and 5XX at Daventry. Following experimental FM stereo transmissions in the
London area in 1958 and regular Saturday morning demonstration transmissions using TV sound
and medium wave radio to provide the two channels, the first regular BBC transmissions using
an FM stereo signal began on the BBC’s Third Programme network on August 28, 1962.
Chicago AM radio station WGN collaborated on an hourlong stereophonic demonstration
broadcast on May 22, 1952, with one audio channel broadcast by the AM station and the
other audio channel by the FM station. New York City’s WQXR initiated its first stereophonic
broadcasts in October 1952, and by 1954, was broadcasting all of its live musical programs
in stereophonic sound, using its AM and FM stations for the two audio channels. Rensselaer
Polytechnic Institute began a weekly series of live stereophonic broadcasts in November
1952 by using two campus-based AM stations, although the listening area did not extend
beyond the campus. Tests of six competing FM-only systems were
conducted on KDKA-FM in Pittsburgh, Pennsylvania during July and August 1960. The Federal Communications
Commission announced stereophonic FM technical standards in April 1961, with licensed regular
stereophonic FM radio broadcasting set to begin in the United States on June 1, 1961.
WEFM and WGFM were reported as the first stereo stations. Television: A December 11, 1952 closed-circuit
television performance of Carmen, from the Metropolitan Opera House in New York City
to 31 theaters across the United States, included a stereophonic sound system developed by RCA.
The first several shows of the 1958–59 season of The Plymouth Show on the ABC network were
broadcast with stereophonic sound in 75 media markets, with one audio channel broadcast
via television and the other over the ABC radio network. By the same method, NBC Television
and the NBC Radio Network offered stereo sound for two three-minute segments of The George
Gobel Show on October 21, 1958. On January 30, 1959, ABC’s Walt Disney Presents made
a stereo broadcast of The Peter Tchaikovsky Story—including scenes from Disney’s latest
animated feature, Sleeping Beauty—by using ABC-affiliated AM and FM stations for the
left and right audio channels. With the advent of FM stereo in 1961, a small
number of music-oriented TV shows were broadcast with stereo sound using a process called simulcasting,
in which the audio portion of the show was carried over a local FM stereo station. In
the 1960s and 1970s, these shows were usually manually synchronized with a reel-to-reel
tape delivered by mail to the FM station. 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, just before MTS
stereo was approved by the FCC. 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 programmes, live and recorded, including the
annual BBC Promenade concerts and the Eurovision Song Contest. The advent of NICAM stereo sound
with TV rendered this unnecessary. Cable TV systems delivered many stereo programs
utilizing this method for many years until prices for MTS stereo modulators dropped.
One of the first stereo cable stations was The Movie Channel, though the most popular
cable TV station that drove up usage of stereo simulcasting was MTV.
Japanese television began multiplex sound broadcasts in 1978, and regular transmissions
with stereo sound came in 1982. By 1984, about 12% of the programming, or about 14 or 15
hours per station per week, made use of the multiplex technology. West Germany’s second
television network, ZDF, began offering stereo programs in 1984.
MTS: Stereo for television 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 video disk.” Multichannel television sound, better known
as MTS, is the method of encoding three additional channels of audio into an NTSC-format audio
carrier. 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, had stereo broadcast capability. Regular stereo transmission of
programs began in 1985. Recording methods
A-B technique: time-of-arrival stereophony This uses two parallel omnidirectional microphones
some distance apart, capturing time-of-arrival stereo information as well as some level difference
information—especially if employed in close proximity to the sound source(s). At a distance
of about 60 cm, the time delay for a signal reaching the first microphone and then the
other one from the side is approximately 1.5 ms. If you increase the distance between the microphones,
you effectively decrease the pickup angle. At a 70 cm distance, it is approximately
equivalent to the pickup angle of the near-coincident ORTF setup.
This technique can produce phase issues when the stereo signal is mixed to mono.
X-Y technique: intensity stereophony Here, two directional microphones are at the
same place, typically pointing at an angle between 90° and 135° to each other. The
stereo effect is achieved through differences in sound pressure level between two microphones.
A difference in levels of 18 dB is needed for hearing the direction of a loudspeaker.
Due to the lack of differences in time-of-arrival/phase ambiguities, the sonic characteristic of X-Y
recordings has less sense of space and depth when compared to recordings employing an A-B
setup. When two figure-eight microphones are used, facing ±45° with respect to the sound
source, the X-Y setup is called a Blumlein Pair. The sonic image produced is realistic.
M/S technique: mid/side stereophony This coincident technique employs a bidirectional
microphone facing sideways and another microphone at an angle of 90°, facing the sound source.
The second microphone is generally a variety of cardioid, although Alan Blumlein described
the usage of an omnidirectional transducer in his original patent.
The left and right channels are produced through a simple matrix: Left=Mid + Side; Right
=Mid − Side. This configuration produces a completely mono-compatible signal and, if
the Mid and Side signals are recorded, the stereo width can be manipulated after the
recording has taken place. This makes it especially useful for film-based projects.
Near-coincident technique: mixed stereophony These techniques combine the principles of
both A-B and X-Y techniques. For example, the ORTF stereo technique of the Office de
Radiodiffusion Télévision Française calls for a pair of cardioid microphones placed
17 cm apart at a total angle between microphones of 110°, which results in a stereophonic
pickup angle of 96°. In the NOS stereo technique of the Nederlandse Omroep Stichting, the total
angle between microphones is 90° and the distance is 30 cm, thus capturing time-of-arrival
stereo information as well as level information. It is noteworthy that all spaced microphone
arrays and all near-coincident techniques use a spacing of at least 17 cm or more.
17 cm roughly equals the human ear distance and therefore provides the same interaural
time difference or more, depending on the spacing between microphones. Although the
recorded signals are generally intended for playback over stereo loudspeakers, reproduction
over headphones can provide remarkably good results, depending on the microphone arrangement.
Pseudo-stereo 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 or, more recently, a combination of
hardware and software. Multitrack Studio, from Bremmers Audio Design, 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, but contributing
to an effect of “widening” original “fattiness” of mono recording.
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.
Binaural recording Engineers make a technical distinction between
“binaural” and “stereophonic” recording. Of these, binaural recording is analogous to
stereoscopic photography. In binaural recording, a pair of microphones is put inside a model
of a human head that includes external ears and ear canals; each microphone is where the
eardrum would be. The recording is then played back through headphones, so that each channel
is presented independently, without mixing or crosstalk. Thus, each of the listener’s
eardrums is driven with a replica of the auditory signal it would have experienced at the recording
location. The result is an accurate duplication of the auditory spatiality that would have
been experienced by the listener had he or she been in the same place as the model head.
Because of the inconvenience of wearing headphones, true binaural recordings have remained laboratory
and audiophile curiosities. However “loudspeaker-binaural” listening is possible with Ambiophonics.
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
Playback Stereophonic sound attempts to create an illusion
of location for various sound sources within the original recording. The recording engineer’s
goal is usually to create a stereo “image” with localization information. When a stereophonic
recording is heard through loudspeaker systems, each ear, of course, hears sound from both
speakers. The audio engineer may, and often does, use more than two microphones and may
mix them down to two tracks in ways that exaggerate the separation of the instruments, in order
to compensate for the mixture that occurs when listening via speakers.
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. 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.
Vinyl records Although Decca had recorded Ansermet’s conducting
of Antar in stereo May 1954 it took four years for the first stereo LPs to be sold. In 1958,
the first group of mass-produced stereo two-channel vinyl records was issued, by Audio Fidelity
in the USA and Pye in Britain, using the Westrex “45/45” single-groove system. Whereas the
stylus moves horizontally when reproducing a monophonic disk recording, on stereo records,
the stylus moves vertically as well as horizontally. One could envision a system in which the left
channel was recorded laterally, as on a monophonic recording, with the right channel information
recorded with a “hill and dale” vertical motion; such systems were proposed but not adopted,
due to their incompatibility with existing phono pickup designs.
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 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. This system was conceived by Alan Blumlein
of EMI in 1931 and was patented in the U.K. the same year, but was not reduced to actual
practice as was a requirement for patenting in the U.S. and elsewhere at that time. EMI
cut the first stereo test discs using the system in 1933, but it was not applied commercially
until a quarter of a century later, and by another company, and dubbed StereoDisk. Stereo
sound provides a more natural listening experience, since the spatial location of the source of
a sound is 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. Compact disc
The Red Book CD specification includes two channels by default, and so a mono recording
on CD either has one empty channel, or else the same signal being relayed to both channels
simultaneously. However, noncommercial CDs in other formats such as White Book or Orange
Book can feature up to four hours of stereo music on one CD for the purposes of extended
programming in public spaces, such as malls. These formats slightly reduce both the sampling
frequency from 44.1 kHz as well as the bit-depth frequency from 16-bit and employ other proprietary
technologies in order to increase the time on the disc and, as in the 16-inch transcriptions
above – render them unplayable on the vast majority of consumer equipment.
Broadcasting Radio
In FM broadcasting, the Zenith-GE pilot-tone stereo system is used throughout the world.
Because of the limited audio quality of the majority of AM receivers, and also because
AM stereo receivers are relatively scarce, relatively few AM stations employ stereo.
Various modulation schemes are used for AM stereo, of which the best-known is Motorola’s
C-QUAM, the official method for most countries in the world that transmit in AM stereo. More
AM stations are adopting digital HD Radio, which allows the transmission of stereo sound
on AM stations. For Digital Audio Broadcasting, MP2 audio streams are used. DAB is one of
the Digital Radio formats that is used to broadcast Digital Audio over terrestrial broadcast
networks or satellite networks. DAB is extended to video, and the new format is called DMB.
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 mono
signals – for example for language studies. 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 decided to start broadcasting in stereo according to the pilot-tone system
in 1977. But stereo radio was delayed in Sweden because of the two competing systems.
Television For analog TV, 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.
Common usage In common usage, a “stereo” is a two-channel
sound reproduction system, and a “stereo recording” is a two-channel recording. This is cause
for much confusion, since five-channel home theater systems are not popularly described
as “stereo”. Most two-channel recordings are stereo recordings
only in this weaker sense. Pop music, in particular, is usually recorded using close miking techniques,
which artificially separate signals into several tracks. The individual tracks 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 to more sophisticated and extensively based on psychoacoustic research. 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 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 is preserved on the recording.
Balance Balance can mean the amount of signal from
each channel reproduced in a stereo audio recording. Typically, a balance control in
its center position will have 0 dB of gain for both channels and will attenuate one channel
as the control is turned, leaving the other channel at 0 dB.
See also Panning. See also
3D audio effect Ambisonics – generalized MS-Stereo to three
dimensions Wave field synthesis – The physically reconstruction
of the spatial sonic field Crossfeed
Hi-fi Joint stereo
Stereo photography Subwoofer
Sweet spot Notes References External links
Online Left/Right Stereo Test Online Stereo Polarity Test
Visualization of All Stereo Microphone Systems with Two Microphones
“Two Ears- Two Loudspeakers?” The limitations of traditional audio

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