STEREO

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 the impression of sound heard from various directions, as in natural hearing. It is often contrasted with monophonic, or "mono" sound, where audio is in the form of one channel, often centered in the sound field (analogous to a visual field).

Stereo recordings are used in FM broadcasting and Digital Audio Broadcasting (DAB) and in several television systems. To record in stereo, sound engineers use various methods, including using two directional microphones, two parallel omnidirectional microphones, or more complex techniques. Several monophonic records such as the original Broadway cast recordings of Oklahoma! (1943), Carousel (1945) and South Pacific (1949), were once re-issued in fake stereo to create the impression that the sound was originally recorded in that medium.

The first stereo transmission was made telephonically by Clement Ader in 1881. The BBC made radio's first stereo broadcast in December 1925. In the 1930s, Alan Blumlein of EMI patented stereo records, stereo films and also surround sound. Harvey Fletcher of Bell Laboratories investigated techniques for stereophonic recording and reproduction. The first commercial motion picture to be exhibited with stereophonic sound was Walt Disney's Fantasia (1940). By the mid-1950s, multichannel sound was common for big-budget Hollywood motion pictures. In 1953, Remington Records began taping some of its sessions in stereo, with the first stereophonic phonograph discs available to the general public in 1958. The US Federal Communications Commission announced stereophonic FM technical standards in April 1961, and licensed regular stereophonic FM radio broadcasting to begin in the United States in 1961. In 1984, Multichannel television sound was adopted by the FCC as the U.S. standard for stereo television transmission.

The word "stereophonic" — derived from Greek stereos = "solid" and phōnē = "sound" — 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 technical usage, stereo or stereophony means sound recording and sound reproduction that uses stereographic projection to encode the relative positions of objects and events recorded. A stereo system can include any number of channels, such as the surround sound 5.1- and 6.1-channel systems used on high-end film and television productions. However, in common use it refers to systems with only two channels. The electronic device for playing back stereo sound is often referred to as "a stereo".