Quadraphonic (or quadrophonic and sometimes quadrasonic) sound – equivalent to what is now called 4.0 surround sound – uses four audio channels in which speakers are positioned at the four corners of a listening space. The system allows for the reproduction of sound signals that are (wholly or in part) independent of one another.
Four channel quadraphonic surround sound can be used to recreate the highly realistic effect of a three-dimensional live concert hall experience in the home. It can also be used to enhance the listener experience beyond the directional limitations of ordinary two channel stereo sound. Quadraphonic audio was the earliest consumer product in surround sound. Since it was introduced to the public in the early 1970s many thousands of quadraphonic recordings have been made.
Quadraphonic sound was a commercial failure when first introduced due to a variety of technical issues and format incompatibilities. Four channel audio formats can be more expensive to produce than standard two-channel stereo. Playback requires additional speakers and amplifier channels. It may also require specially designed decoding equipment.
The introduction of home cinema products in the 1990s were first intended for movie sound, but also brought multi-channel music reproduction into popularity again. By this time new digitally based formats had been created. Many four channel recordings from the 1970s have been reissued in modern surround sound systems such as Super Audio CD, DTS, Dolby Digital, DVD-Audio and Blu-ray. Multichannel home audio reproduction has experienced a revival since 2000 and new four channel recordings have also been released to the public since this time.
A quadraphonic system will reproduce left front, left rear, right front, and right rear audio signals in four separate speakers. The reproduction capability of the rear speakers should be of the same quality or almost the same quality as the front speakers; ideally, a quadraphonic system uses four identical speakers.
History
The first machines used for 4-channel sound recording were analog reel-to-reel tape recorders. These were developed for use by audio engineers in professional studios during the 1950s in Germany by Telefunken and also by Ampex in the United States. Such machines appeared in some European electronic-music studios by 1954.
Early attempts to reproduce four channel sound for home playback began with audio laboratory engineers in the late 1960s. Producer Thomas Mowrey, initially working at the Eastman School of Music, was one of the pioneers of classical quadraphonic recording. He later made quadraphonic productions for Deutsche Grammophon and other labels in the early 1970s, but many of these were released only as stereo recordings.
A small number of quadraphonic recordings were introduced to the American consumer market by Vanguard Records in June 1969 on reel-to-reel tape. The most popular medium used to market recordings to the public during the 1970s was the vinyl LP phonograph record. Quadraphonic recordings on 8-track tape were also popular in the 1970s, particularly among car audio enthusiasts.
In the 1970s specialized hardware systems were marketed by major electronic manufacturers to the public for decoding 4-channel recordings. These decoders were often sold as separate electronic components. Decoders were also available as built in features of some audio receivers or amplifiers sold during the 1970s.
Many quadraphonic recordings in the 1970s used "matrix" technologies to encode and decode four channels of audio information in a 2-channel medium, usually an LP. The poor decoding performance of early matrix formats was the main reason they disappeared once improved matrix systems arrived. The later matrix systems were based on work by Peter Scheiber. His basic formula used 90° phase-shift circuitry to enable enhanced 4–2–4 matrix systems to be developed, of which the two main leaders were Columbia's SQ and Sansui's QS systems.
The three most popular quadraphonic LP formats in the 1970s were SQ (Stereo Quadraphonic), QS (Regular Matrix) and CD-4 (Compatible Discrete 4) / Quadradisc.
The Japanese governing body and audio hardware manufacturers defined standards for quadraphonic sound. RM (Regular Matrix) was used a synonym for QS, QM (Quadraphonic Matrix was used for Stereo-4 and Dynaquad) and QX (QuadXtra, based on D.H. Cooper "Dual-Triphonic") for UD4.