QS Regular Matrix

Quadraphonic Sound (originally called Quadphonic Synthesizer, and later referred to as RM or Regular Matrix) was a matrix 4-channel quadraphonic sound system for phonograph records. The system was based on technology created by Peter Scheiber, but further developed by engineer Ryosuke Ito of Sansui in the early 1970s.
The technology was freely licensed and was adopted by many record labels including ABC, Advent, BluesWay, Candide, Command, Decca, Impulse, Longines, MCA, Passport, Pye, Turnabout and Vox. Many recordings using this format were released on vinyl LP records during the 1970s.
"Regular Matrix" was often used a synonym for QS, but was actually a standard set by the Japanese governing body, which also embraced the QM and QX matrix systems.
The QS matrix has been found to offer the advantages of excellent diagonal separation and stereo compatibility, and although the adjacent speaker separation is only 3 dB, this symmetrical distribution produces more stable quadraphonic images than some other matrix systems. The QS record track width is as narrow as a conventional stereo track, so the maximum playing time is the same as conventional stereo records. If the four channels are decoded and afterwards re-encoded to one channel, a normal mono sound with no loss results. QS was the only matrix system that could do that perfectly.
History.
As early as 1969 engineer and musician Peter Scheiber developed a matrix system very similar to QS. He also was instrumental in many improvements to SQ quality, in collaboration with Martin Willcocks and Jim Fosgate.
In the early 1970s Sansui introduced the Four Channel Synthesizer Decoder QS-1 and the QSE-1 Encoder based on the QS system in Japan and debuted export to the United States in March 1971. The channel separation was only 3 dB, but because of the human way of hearing it sounded relatively good.
In 1973 Sansui introduced the "QS Vario Matrix decoder" with 20 dB separation in all directions. (The "Vario Matrix decoder" could also play SQ records on "Phase Matrix" mode with 6 dB separation. Later Sansui used front-rear logic on the SQ mode.) Two outboard decoders, the "QSD-1" and "QSD-2", as well as the "QRX" series of larger receiver-amplifiers, incorporated this matrix and up-conversion. Sansui's QS decoders also had good stereo-to-quad capabilities, wrapping the L-R panorama to LB-LF-RF-RB in a horseshoe topology. (The "Vario Matrix" decoder could synthesize four channel sound with high separation - at least 12 dB.)
The system was often called RM (Regular Matrix) when used on amplifiers or receivers by other trademarks than Sansui. Many Japanese brands like Pioneer or Kenwood had matrix decoders with two modes: - SQ and RM. JVC had two modes on their matrix decoder called Matrix 1 and Matrix 2. That decoder could play both SQ and QS records, but it was a simplified decoder. QS records could also be played on Marantz Vari-Matrix system. (European trademarks like Philips or Bang & Olufsen had only decoders for SQ or both SQ and CD-4 - but not QS.) QS records could give some quadraphonic effect, although far from accurate, when played on an SQ decoder.
The QS matrix technology was used to create the five-channel sound system used for première theater engagements of the 1975 film "Tommy."
In June 2018 electronic musician Suzanne Ciani released the album "LIVE Quadrophonic" using the QS Regular Matrix system. A limited edition of 227 boxed set copies were released as a 12 inch 45 RPM phonograph record. The box also includes a hardware decoder for correct playback, made by Involve Audio. This was one of the first new quadraphonic phonograph recordings to be released since the late 1970s.
Usage.
"j = + 90° phase-shift"
When played on a conventional two channel stereo equipment, the front channels are narrower than ordinary two channels because of the low separation. But the rear channels are heard from points outside the ordinary stereo spectrum. So the QS record gives a totally broader stereo picture than conventional two channel stereo. The point behind the listener is out of phase when played in two channel stereo and extinct in one channel mono listening. In mono the volumes of left and right points behind the listener is reduced with only 3 dB (in SQ 6 dB).
(Source: Kjell Stensson: 4-kanalstekniken ännu i startgroparna, in Stereo Hi Fi Handboken 74, Svenska HiFi Institutet 1973, page 30).
Quintaphonic Sound.
A five-channel system based on QS, named Quintaphonic Sound, was used for the 1975 film "Tommy". The left and right 35mm magnetic soundtracks were QS encoded to create four channels around the cinema audience, while the centre mag track was assigned to the speaker behind the screen. The mag FX track was unused. This channel layout (5.0) was similar to the now common 5.1 surround sound configuration.
Hardware.
The QSD-1 Quadphonic Synthesizer was introduced in 1971, soon followed by the smaller, boxy QSD-2.
As of 2018 the Australian company Involve Audio is making a QS decoder called Surround Master, which claims to use the same specifications as the QSD-1. The decoder included with the Suzanne Cianni album used this technology.