Quadraphonic sound

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 right front, right rear, left front, and left 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[edit]

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.^[1]


Early attempts to reproduce four channel sound for home playback began with audio laboratory engineers in the late 1960s. Producer Thomas Mowrey,^[2] 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.^[3]


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^[4][5] was used for Stereo-4 and Dynaquad) and QX (QuadXtra, based on D.H. Cooper "Dual-Triphonic")^{[6][7][8][9][10]} for UD4.^[11]


With Scheiber and Martin Willcocks, Jim Fosgate developed the Tate II 101 SQ decoder, which produced a very accurate sound field by using gain riding and the Haas effect to mask decoding artifacts. It used custom, hand-assembled and ‑calibrated circuitry with components sorted to 1%, for exact performance. Sansui's QSD-series decoders and QRX-series receivers were very good, even synthesizing left-right stereo into a ⋂ horseshoe topology. However, all these came too late in the game and were too expensive or difficult to procure for public purchase, to rescue matrix quad from obscurity.


By the early 2000s more sophisticated "discrete" multichannel systems had mostly replaced matrix technologies, providing a higher level of performance and full channel independence. Today, software can be used to take the place of hardware decoding. Modern software algorithms are capable of more accurate decoding performance than the earlier hardware technologies.


All of the multichannel audio systems in common use today are digital systems. Digital multichannel audio has been available for the home since the introduction of surround sound movies in the 1990s using Dolby Digital and DTS. The most common digital media capable of reproducing surround sound music today are Super Audio CD, DVD, and Blu-ray, all of which are capable of playing high-resolution audio with multiple channels.

Quadraphonic audio mixing[edit]

The audio mixing process for four channel sound is different than for stereo versions of the same recording. Most studio equipment is designed for stereo only, so specialized multichannel mixing consoles and playback systems must be available.


For classical music, producers have typically preferred an effect where the orchestra appears in stereo in only the front channels, and the natural reverberation or "echo" of the concert hall is in all the speakers. Some live concert recordings of popular music have also been mixed this way. Classical recordings rarely place primary or solo instruments in the rear channels, though it is done occasionally.


A few classical recordings have been made from a perspective in which the listener seems to be seated in the middle of the orchestra. One example is the 1973 Columbia Masterworks recording of Béla Bartók's Concerto for Orchestra, conducted by Pierre Boulez.^[12] The original four channel recording was released on matrix LP and 8-track tape, and reissued on the Super Audio CD format by Dutton Vocalion in 2018.^[13] Notes supplied with the recording indicate the direction from which each group of instruments can be heard.


Pop, rock and jazz music producers have tended to employ a mixing style with a relatively high degree of musical separation between the four channels. This type of recording may place musical sounds in the rear channels that are of equal importance to the front channels. It can expand on the listener's sense of direction and spaciousness in a way similar to what happened when recording engineers introduced stereo recording. In some four channel recordings sounds move in full rotation around the listener.


Mixing engineers can also aim for a hybrid effect between styles. While quadraphonic effects have sometimes been considered artificial, musical enjoyment can be dramatically enhanced by more fully involving the listener.