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Analog Quadraphonic Formats

Quadraphonic sound uses four channels in which speakers are positioned at all Four Corners of the listening space.

Quad was not one format but myriad different and largely incompatible formats on different media: quadraphonic could be obtained from vinyl records, eight tracks, and reel-to-reel. Further complicating quadraphonic was the fact that some systems were discrete, while others were matrix.

Quad in its original form was a commercial failure, the LP formats were plagued with technical problems, most of which were solved too late to save Quad. It also was more expensive, and required extra speakers, which became a decorating problem. It also suffered from lack of a standard format for LP records. However, quite a few recordings were made before its demise. It was only the rise of home theater products in the late 1980s and early 1990s that brought multi-channel recording formats back to the forefront, albeit in a completely different and perhaps unexpected form.

Discrete Quad Formats

CD-4 / Compatible Discrete 4 / Quadradisc

Compatible Discrete 4 (CD-4) or Quadradisc was introduced in 1971 as a discrete quadraphonic system created by JVC (as a subsidiary of RCA). Record companies who adopted this format include Arista, Atlantic, Capricorn, Elektra, Fantasy, Grunt, JVC, Nonsuch, RCA, Reprise, and Warner Brothers. This format was less popular than others because of incompatibility, poor longevity and strict setup requirements. The quadraphonic music was encoded with sum and difference signals in the ultrasonic range on the standard stereo grooves of vinyl. To play back the record, a special high-frequency cartridge and stylus was required, in addition to a CD-4 demodulator and the usual quadraphonic receiver or amplifier. This system produced additional wear and tear, so JVC introduced "super vinyl", a very durable type of record. The cartridge used had a Shibata type stylus and an extended frequency response. Later, linear contact styli were developed that improved the performance of CD-4 systems. However, this development came too late to save CD-4 from extinction. CD-4 records could be played as stereo records if care was taken to use a Shibata (or linear contact) stylus to protect the subcarrier modulations.

UD-4 / UMX

UD-4/UMX - Developed by Nippon/Columbia. Very few items are encoded in this format and it was marketed only in the UK, Europe and Japan. A regular matrix decoder could be used to playback this recordings, but by adding a special cartridge and an UD-4 demodulator separation and performance of the system increased. UD-4 systems split the audio spectrum into two bands. The lower frequencies were encoded with subcarriers similar to the CD-4 system. The upper band was matrix encoded. The subcarriers for the lower band were placed above the upper band frequencies and were supersonic. UD-4 was not as critical in its setup than CD-4, because the subcarriers did not have to carry the higher frequencies as is true with CD-4.

Quad-8 / Quadraphonic 8-Track

Quadraphonic 8-Track was a discrete system introduced by RCA in late 1970. The format was almost identical in appearance to stereo 8-tracks except for a small notch in the upper left corner of the cartridge. This signaled a quadraphonic 8-track player to combine the odd tracks as audio channels for Program 1 and the even tracks as channels for Program 2. The format was not entirely compatible with stereo or mono players - although quadraphonic players would play stereo 8-tracks, playing quadraphonic tapes on stereo players results in hearing only one-half the channels at a time. Some stereo 8-track players touted simulated quadraphonic sound (through upmixing stereo 8-tracks) but were not quadraphonic 8-track players. The last release in the quadraphonic 8-track format was in 1978.

Quadraphonic Reel to Reel

Often judged by audiophiles to be the best of the old Quad formats, this system was based on a reel to reel type 1/4" tape format, fully discrete and with full bandwidth (Unlike the Q8 Cartridge system, which had limited dynamic range). This format was only available in the USA. Playback machines were either dedicated quad machines, or 4-track open reel systems usually running at a speed of 7.5 IPS (double the speed of the 8-Track systems), giving even better sound quality.

Matrix Quad Formats

SQ / Stereo Quadraphonic

Stereo Quadraphonic was a matrix quadraphonic system for vinyl. It was introduced by CBS in 1972 and record companies who adopted this format include Angel, Capitol, CBS, CTI, Columbia, EMI, Epic, Eurodisc, Harvest, HMV, Seraphim, Suprophon, and Vanguard. The system is based on the work of Peter Scheiber, who created the basic mathematical formulas used to matrix four channels into two in 1970. This makes sense since without a quad decoder SQ encoded records play as a normal stereo record and CBS stated their desire to maintain excellent compatibility of their SQ encoded records with standard stereo systems. Additionally - and perhaps most importantly - these type of records along with the QS format, allowed the full bandwidth from 20 Hz to 20 kHz to be used, giving a much more "open" & detailed top end.

The early days of SQ were marred by the fact that early SQ decoders couldn't produce more than 3 dB of separation from front to back. By the time "Logic" circuits had been introduced to enhance separation, quad had already been considered a failure. The pinnacle of SQ decoder development was the Tate Directional Enhancement System, which was implemented in decoders produced by Audionics of Oregon and Fosgate. These units are sought by SQ collectors for their superior performance.

A Prologic II decoder will recover some of the surround information present on a SQ mix, as the matrices used are somewhat similar.

QS / Quadraphonic Stereo

Quadraphonic Stereo was a system that was conceptually very similar to SQ, but developed independently by engineer Isao Itoh of Sansui, adopted by ABC, Advent, Bluesway, Candide, Command, Decca, Impulse, Longines, MCA, Ovation, Pye, Turnabout and Vox record companies. It was freely licensed to record companies but was rarely found on receivers other than Sansui. The QS matrix is found to offer the advantage of excellent diagonal separation and, though the adjacent speaker separation is only 3dB, this symmetrical distribution produces more stable quadraphonic images.

EV / Stereo-4

EV - Developed by Electro Voice, also known as Stereo-4. Despite heavy promotion by Radio Shack stores in the USA, very few items were encoded in this format. Stereo-4 decoders were especially good at producing credible 4-channel effects from 2-channel stereo recordings.

Matrix H

Matrix H was a system developed by BBC engineers to carry quadraphonic sound via FM radio in a way that would be compatible with existing mono and stereo receivers. Several quadraphonic programs were made for Radios 3 and 4, while Radio 1 carried quadraphonic session recordings by various bands. It was merged with the ambisonic 45J format to produce the two-channel version of UHJ.

UHJ / B-format

In Ambisonics B-format, known as first-order Ambisonics, sound information is encoded into 4 channels. Ambisonics UHJ coding can be used to produce stereo compatible Ambisonic records, tapes and broadcasts.

Passive Pseudo Quad

Passive Pseudo Quad can be much more realistic than would appear from the name. It has been observed that ambient sounds in a concert, such as applause or even coughs from the audience, are generally received in "opposite phase" by the stereophonic microphones, while sound from the musicians is generally in "synchronous phase". Thus, if rear speakers are fed with the difference between the stereo channels, audience noises and echoes from the auditorium can be heard from behind the listener. This can be most easily achieved by wiring two similar additional rear speakers in series (typically 8+8=16 ohms) between the live feeds to the front speakers. This arrangement was colloquially known as the "Hafler hookup," after audio engineer David Hafler, an early proponent of the idea. The "crosstalk" or loss of stereo separation in the front speakers is less than 2dB while the rear sound level in a typical stereo-recorded live performance is about 7dB below the front, but clearly audible. This "passive" method is arguably as good as any of the expensive "active matrix" electronic decoders that attempt to reconstruct ambient sound from a stereo recording.