SQ Quadraphonic or SQ was a matrix 4-channel system for vinyl.. It was introduced
by CBS Records in 1971 and record companies who adopted this format included Angel,
Columbia (in Europe called CBS Records), EMI, Epic, Eurodisc, Harvest, HMV, Seraphim,
Supraphon and Vanguard.
Early SQ decoders could not produce more than 3dB of separation from front to back.
The early "Logic" circuits which were introduced to enhance separation to 20dB, provided
poor performance with very noticeable gain-pumping and an unstable 'swaying' sound
stage. The SQ system also faced resistance from broadcasters since, whilst essentially
a two-channel system and stereo-compatible, it could have significant mono compatibility
issues which could pose serious problems with televisions and monophonic radios of
CBS stated a desire to maintain excellent compatibility between their SQ-encoded
records and standard stereo systems. In practice, there were stereo compatibility
problems as a result of the 4-channel encoding/decoding process. When played on
two channel stereo equipment, the front 2 channels were normal stereo, but there
were some aberrations. The rear channel information narrowed in stereo compared to
the front channels, but the real problems occurred with the sounds in the centre.
The mid centre point, originally recorded in quadraphonic mode, now only appeared
in the left speaker. The point right behind the listener was out of phase in two
channel stereo and missing altogether in one channel mono listening. The left rear
and right rear points were 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 was also broader than a conventional stereo track, so the maximum
playing time was lower than a conventional stereo record.
Columbia/CBS Records had a catalogue of four channel records called “Quadraphonic”
with a golden frame on the album covers. These records were encoded with the SQ system,
but there was also a parallel Quadraphonic catalogue for 8-track tapes, mainly aimed
at the car stereo market. These quadraphonic tapes were made in discrete four channel
stereo, which gave the whole CBS Quadraphonic project a higher status, bearing in
mind the popularity of 8-track at the time.
The Directional Enhancement System, also known as the Tate DES, was an advanced decoder
for SQ (although it could be made to work with any matrix system), and this enhanced
the directionality of the basic SQ matrix. Unfortunately, it's relatively late arrival
didn't help the survival of SQ. It was also rather expensive.
Sometimes the SQ system (and other similar matrix systems) were called “Phase Matrix”,
as opposed to QS and similar systems which were called “Regular Matrix”.