Quadraphonic (or Quadrophonic and sometimes Quadrasonic) sound – equivalent to what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are (wholly or in part) independent of one another. Quadraphonic audio was the earliest consumer product in surround sound and thousands of quadraphonic recordings were made during the 1970s.
It was a commercial failure due to many technical problems and format incompatibilities. Quadraphonic audio formats were more expensive to produce than standard two-channel stereo. Playback required additional speakers and specially designed decoders and amplifiers.
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Quadraphonic audio reproduction on vinyl records was problematic. Some systems used a demodulator to decode discrete sound channels. This allowed for full channel separation, although such systems were prone to reduced record life. Other systems used matrix decoding to recover four channels from the two channels cut on the record. Matrix systems do not have full channel separation, and some information can be lost between the encoding and decoding processes. Both discrete and matrix quadrophonic recordings could be played in two channels on conventional stereo record players.
There were less sophisticated "derived" solutions that only provided back ambience channels, not a defined placement of individual instruments.
Quadraphonic systems based on tape were also introduced, based on new equipment capable of playing four discrete channels. These recordings were released in reel-to-reel and 8-track cartridge formats.
A full, four-channel (quadraphonic) system will reproduce the left front, left back, right front, and right back audio signals in each of four separate speakers. Regardless of discrete or matrix formats, in four-channel stereo the rear speakers should be of the same or almost-same size or quality and have the same or almost-same frequency range as the front speakers.
Discrete (4-4-4) formatsEdit
Discrete reproduction is the only true quadraphonic system. As its name suggests, with discrete formats the original four audio channels are passed through a four-channel transmission medium and presented to a four-channel reproduction system and fed to four speakers. This is defined as a 4–4–4 system.
- Q4 / quadraphonic reel to reel (1969)
- quad-8 (Q8) / quadraphonic 8-track (1970)
- CD-4 (Compatible Discrete 4) / Quadradisc (1972)
- UD-4 / UMX / BMX (1974)
Matrix (4-2-4) formatsEdit
With matrix formats, the four channels are converted (encoded) down to two channels. These are then passed through a two-channel transmission medium (usually an LP record) before being decoded back to four channels and presented to four speakers. To transmit four individual audio signals in a stereo-compatible manner, there must be four simultaneous linear equations to reproduce the original four audio signals at the output. The term compatible indicates that:
- A single-channel (mono) system will reproduce all four audio signals in its one speaker.
- two-channel (stereo) system will reproduce the left front and left back audio signals in the left speaker and the right front and right back signals in the right speaker.
The original systems (DY and EV-4) were basic and suffered from low front left-right separation (around 12 dB) and a poor rear left-right separation of 2 dB. The decoders were designed more to give an effect rather than accurate decoding, which was mainly due to limitations in both systems, although as both systems were very closely related mathematically, users only needed one decoder of either system to play back albums of both systems.
The poor decode performance of these matrix formats was the main reason for their disappearance once the improved matrix systems arrived based on the work by Peter Scheiber. His basic formula utilized 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. 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.
The differences between the original systems and the new were so vast, it made decoding DY/EV-4 with either SQ or QS decoders with any accuracy, impossible; the results being just a form of artificial quad.
 This 4:2:4 process could not be accomplished without some information loss. That is to say, the four channels produced at the final stage were not truly identical to those with which the process had begun.
- Matrix H (1977)
- SQ / Stereo Quadraphonic (1971)
- QS (Quadraphonic Sound)/ RM (Regular Matrix) (1971)
- DY / Dynaquad (used as an encoding format on some records) (1971)
- EV / Stereo-4 (1970)
Derived (2-2-4) formatsEdit
Derived (2-2-4) formats were inexpensive electronic solutions that provided back ambience channels from regular stereo records. There was no deliberate placement of individual instruments on the back channels.
Discrete tape formatsEdit
Quadraphonic open reel tape (Q4)Edit
The first medium for four-channel sound was reel-to-reel tape, used first in European electronic-music studios by 1954, an outstanding example of which was the tape part of Karlheinz Stockhausen's piece, Kontakte (1958–60), and was introduced to the American market by the Vanguard Recording Society in June 1969 as "Quadraphonic open reel tape (Q4)" tapes.[failed verification] All available four tracks were used in one direction on the tape, running at twice the speed of the regular four-track reel-to-reel tapes.
Quadraphonic 8-Track Tape (Q8)Edit
RCA Records followed, in April 1970, with its announcement of a four-channel version of the 8-track tape, named Quad-8 or Quadraphonic 8-Track Tape (later shortened to just Q8). These eventually appeared in Sept. 1970. There were automobile players as well as home versions.
The format was almost identical in appearance to stereo 8-tracks, except for a small sensing notch in the upper left corner of the cartridge. This signaled a quadraphonic 8-track player to combine the odd tracks as audio channels for program 1, and the even tracks as channels for program 2. The format was not backward-compatible with stereo or mono players; although quadraphonic players would play stereo 8-tracks, playing quadraphonic tapes on stereo players resulted in hearing only one-half the channels at a time.
The last release in the quadraphonic 8-track format was in 1978, although most had stopped appearing by the end of 1976.
Matrix vinyl formatsEdit
Quadraphonic records did not remain restricted to the discrete-channel format used in reel-to-reel or 8-track tapes. Quadraphonic vinyl albums appeared, using several different and incompatible recording modes.
EV-4/Stereo-4 and Dynaco (DY)Edit
The first of these were basic systems with poor performance developed by Electro-Voice (EV-4/Stereo-4) and Dynaco (Dynaquad (DY)). A so-called matrix format, it utilized four sound channels which were "encoded" into two stereo album tracks. These were then "decoded" back into the original four sound channels, but with poor decode performance which failed to match the discrete formats.
QS Regular Matrix and SQ QuadraphonicEdit
The first of these, known as QS, was developed by Sansui Electric. A so-called matrix format, it utilized 4 sound channels, which were "encoded" into two stereo album tracks. These were then "decoded" back into the original four sound channels. The QS system debuted in the United States in March 1971 and was improved by their Vario-Matrix system in 1973.
The second, SQ, was developed and marketed by Columbia Records and Sony and entered the US market in April 1971. The SQ format was also used by companies such as EMI in Great Britain, who pressed several SQ album releases. The sound separation of the SQ system was greatly improved by the introduction of SQ Full Logic decoding in 1975 using the Motorola chips MC1312, MC1314 & MC1315.
Discrete vinyl formatsEdit
CD-4 or QuadradiscEdit
This quadraphonic format was first marketed in the United States in May 1972. A fully discrete sound mode, it eschewed the previous matrix systems in favor of a more complex method of four-channel reproduction. It encoded surround information in ultrasonic sound above 20 kHz, requiring a special cartridge with a Shibata stylus, then used its own demodulator and decoder to retrieve the original sound field.
UD-4 / UMX / BMXEdit
The system suffered from incompatibility with regular stereo playback due to phase differences between the left and right channels.
UD-4 was less critical in its setup than CD-4 because the carriers did not have to handle frequencies as high as those found in the CD-4 system.
Radio broadcast formatsEdit
One radio series, Double Exposure, was briefly syndicated throughout the United States to various FM stations; it was made up of jazz, rock and pop music which had been commercially released in one of the quadraphonic record or tape systems.
One of the longest-lived radio broadcasts was WQSR-FM "Quad 102½" in Sarasota, Florida. Throughout most of the 1970s this station broadcast a signal which could be tuned as two separate stations with conventional stereo receivers.
In addition, San Francisco classical music station KKHI-FM broadcast the San Francisco Opera in "compatible" (that is, matrix-encoded) quadraphonic format during the 1970s, as did Chicago station WFMT's live "Chicago Lyric Opera" broadcasts.
The existing matrix formats were tested first. The "H" has no meaning; they called the first matrix assessed Matrix A, and then worked through the alphabet. Matrix H emerged as the best solution for mono compatibility and radio transmission, yet there was no specific commercially available decoder for it.
The BBC later cooperated with the developers of Ambisonics to produce BBC/NRDC System HJ. This was based on tolerance zones designed to include modified versions of both Matrix H and the prototype two-channel encoding of Ambisonics, known as System 45J. Subsequently, the Nippon-Columbia UMX matrix was brought into the standard, leading to the final UHJ name now associated with Ambisonics.
In 1976, Ben Bauer integrated matrix and discrete systems into USQ, or Universal SQ (others had also done this with their quad systems).
It was a hierarchical 4-4-4 discrete matrix which used the SQ matrix as the baseband for discrete quadraphonic FM broadcasts using additional difference signals called "T" and "Q". For a USQ FM broadcast, the additional "T" modulation was placed at 38 kHz in quadrature to the standard stereo difference signal and the "Q" modulation was placed on a carrier at 76 kHz.
For standard two-channel SQ Matrix broadcasts, CBS recommended that an optional pilot-tone be placed at 19 kHz in quadrature to the regular pilot-tone to indicate SQ encoded signals and activate the listener's logic decoder. CBS argued that the SQ system should be selected as the standard for quadraphonic FM because, in FCC listening tests of the various four-channel broadcast proposals, the 4:2:4 SQ system, decoded with a CBS Paramatrix decoder, outperformed 4:3:4 (without logic) as well as all other 4:2:4 (with logic) systems tested, approaching the performance of a discrete master tape within a very slight margin. At the same time, the SQ "fold" to stereo and mono was preferred to the stereo and mono "fold" of 4:4:4, 4:3:4 and all other 4:2:4 encoding systems.
In 1967 the rock group Pink Floyd performed the first-ever surround-sound rock concert at “Games for May”, a lavish affair at London’s Queen Elizabeth Hall, where the band debuted its custom-made quadraphonic speaker system. The control device they had made, the Azimuth Co-ordinator, is now displayed at London's Victoria and Albert Museum, as part of their Theatre Collections gallery.
The rise of home theatre products in the late 1980s and early 1990s brought multi-channel audio recording back into popularity, although ultimately in new digitally based formats. Many of the 1970s quadraphonic recordings have been reissued in modern surround sound systems such as DTS, Dolby Digital, DVD-Audio and Super Audio CD.
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