QS Regular Matrix

Quadraphonic Sound (originally called Quadphonic Synthesizer, and later incorrectly referred to as RM or Regular Matrix) was a phase amplitude matrix 4-channel quadraphonic sound system for phonograph records.

It provided 4 channel output (Front Left, Front Right, Back Left and Back Right) from a specially encoded standard stereophonic track. 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. More than 600 LP record titles using this technology were released on vinyl during the 1970s.