Quad hit the marketplace in a big way in 1971. Vanguard Records was one of the early players with their 4-channel reel-to-reel tape. Articles in various magazines from the period of around 1969 to 1970 mention quad sound from reel-to-reel tape. Quad from vinyl records and FM broadcasts is mentioned as being possible in the future.
Quad on tape is usually a discrete-type quad. True discrete quad uses 4 individual audio sources from input to output.
The earliest attempts to obtain quad from vinyl records used the OOPS phenonenom… Out of Phase Stereo. To avoid excess technicality, OOPS extracted “hidden” sound from stereo recordings. The earliest quad decoders were based on the OOPS effect. A few vinyl records were purposefully recorded to maximize the OOPS effect. Purposely created encoded quad vinyl records hit the market in 1971 with some sources stating it was 1970.
Quad purposely encoded onto vinyl is often called matrixed quad. The earliest version was EV-4 with the “EV” standing for ElectroVoice… a hardware manufacturer. Later matrix quad types were CBS’s SQ, Sansui’s QS. Matrixed quad blends 4 audio channels into two channels for placement on a vinyl record. The matrix decoder separates the two blended-in rear channels of audio. CD-4 is handled differently, not being a true matrix-type quad. Many consider it a discrete-type though it suffers from some of the bleed-over problems inherent with the matrix-type.
Many quad decoders and receivers use circuitry designed by the manufacturer to synthesize quad sound from a stereo source. Though the regular decoder was capable of synthesizing quad, extra circuitry was often added to enhance the synthesized quad effects created from a stereo input. Sansui’s Vario-Matrix circuitry was one of the more succesful attempts while other brands functioned well to marginal at best. Here is a partial list of some of the names manufacturers used in naming their synthesizing circuitry:
2+2 4-D Adapter Ambiophonic Composer Dual Triphonic MultiSonic Quadaptor Quadio Quadralizer Quadrix Quatrasonic Quatravox Stereo-4 VariBlend Vari-Matrix Vario-Matrix, and more !!!!