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SQ Quadraphonic ("Stereo Quadraphonic") was a matrix 4-channel quadraphonic sound system for vinyl. It was introduced by CBS Records (in America Columbia Records) in 1971. Record companies, who adopted this format include: Angel, CTI, Columbia (in Europe called CBS Records), EMI, Epic, Eurodisc, Harvest, HMV, Seraphim, Supraphon and Vanguard. With Matrix formats, the four sound channels (forward left, forward right, back left, back right) are converted (encoded) down to two channels (left, right). 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. The SQ encoding is based on the work by Peter Scheiber and further developed by Benjamin Bauer. His basic formula utilized 90 degree phase shift circuitry to enable enhanced 4-2-4 matrix systems to be developed. 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. In 4-2-4 matrix four channel stereo, the rear speakers should be of the same or almost same size quality and have the same or almost same frequency range as the front speakers. ==Usage== The early SQ decoders could not produce more than 3 dB of separation from front to back. Early "Front-rear logic" circuits were introduced to enhance separation to 12 dB and later "Full logic" circuits 20 dB, but both provided poor performance, very noticeable gain-pumping and an unstable 'swaying' sound field.〔http://www.ka-electronics.com/images/pdf/CBS_Motorola_SQ_Decoders.pdf〕 The SQ system also faced resistance from broadcasters since, while essentially a two-channel system and totally stereo-compatible, it could have substantial mono compatibility problems, which posed serious problems with all televisions and monophonic radios of the era. By the time that the most advanced logic system was introduced for SQ, the ''Tate Directional Enhancement System'',〔Willcocks, Martin E. G. (March 1974), "Directional Enhancement System for Quadraphonic Decoders". or .〕 "quad" was already considered a failure. Harman Kardon had an SQ decoder that could change the separation so it was as low between the front channels as the separation between front and rear channel. Some of the SQ mixes are still present on CDs, especially on early, non-remastered editions, on which the original master is, in itself, SQ. (SQ is compatible with two-channel stereo, so there was no need to create a stereo version.) ''j = + 90° phase-shift'' To provide mono-compatibility a variation on this matrix was proposed: ''j = + 90° phase-shift'' The four channels were encoded and decoded normally in this proposal, but the back-center channel was coded in phase and therefore decoded in front-center. This system made good sense, as, in the absence of a quad decoder, SQ-encoded records would play almost as normal stereo records, and CBS stated their desire to maintain excellent compatibility between their SQ-encoded records and standard stereo systems. In practice, there were compatibility problems. When played on a two channel stereo equipment, the front channels sounds like ordinary two channel stereo channels. The rear channels are narrower than the front channels. The problem occurs with the sounds in the center. The point right behind the listener is out of phase in two channel stereo and extinct in one channel mono listening. The left rear and right rear points are 3 dB lower in two channel stereo listening and 6 dB lower in mono listening. (Source: Kjell Stensson: 4-kanalstekniken ännu i startgroparna, in Stereo Hi Fi Handboken 74, Svenska HiFi Institutet 1973, page 31). The SQ record track is broader than a conventional stereo track, so the maximum playing time is lower than a conventional stereo record. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stereo Quadraphonic」の詳細全文を読む スポンサード リンク
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