24: Introduction of stereo sound to recorded music
Stereophonic sound, commonly called stereo, is the reproduction of sound, using two or more independent audio channels, through a symmetrical configuration of loudspeakers, in such a way as to create a pleasant and natural impression of sound heard from various directions, as in natural hearing. It is often contrasted with monophonic (or “monaural” or just mono) sound, where audio is in the form of one channel.
The word “stereophonic” is derived from Greek and was coined by Western Electric, by analogy with the word “stereoscopic”. In popular usage, stereo usually means 2-channel sound recording and sound reproduction using data for more than one speaker simultaneously.
In the 1930s, Harvey Fletcher of Bell Laboratories investigated 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 eighty 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 Prometheus: Poem of Fire, is the earliest surviving 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. Leopold Stokowski, normally the orchestra’s conductor, was present in Constitution Hall to control the sound mix. Bell Labs also demonstrated binaural sound, using a dummy with microphones instead of ears, at the Chicago World’s Fair in 1933.
Two stereophonic recording methods, using two channels and coincident microphone techniques were developed by Alan Blumlein at EMI in 1931 and patented in 1933. A stereo disc, using the two walls of the groove at right angles to carry the two channels, was cut at EMI in 1933, twenty-five years before that method became the standard for stereo phonograph discs.
In the sixties, record companies believed that all songs on a stereo album should sound like stereo. If a stereo master was not available, companies would often create a simulated stereo mix.
Duophonic is also a term used to refer to a sound process by which a monaural recording is turned into a kind of “fake stereo” by splitting the signal into two channels, delaying the left and the right channnels by means of delay lines and other circuits (desynchronizing them by fractions of a second), and cutting the bass frequencies in one channel with a high-pass filter, then cutting the treble frequencies in the other channel with a low-pass filter. The end result was a synthesized stereo effect, without giving the listener the true directional sound characteristics of real stereo.
“Duophonic” was used as a trade name for the process by Capitol Records for re-releases of mono recordings in the mid-to-late 1960s through the 1970s. Capitol execs used these synthesized stereo LPs as a way of filling retailer’s shelves with stereo product, fooling many consumers into believing the records were true stereo.
The process was used for some of their biggest releases, including a variety of albums by The Beach Boys and Frank Sinatra. Unfortunately, over the years, some Duophonic tapes were confused with true stereo recordings in Capitol Records’ vaults, and wound up getting accidentally reissued on CD throughout the 1980s and 1990.
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October 18th, 2007 at 12:37 pmhttp://www.whatgoeson.com/features/the-beatles/the-capitol-albums-duophonic-delights-and-mono-mishaps.html