From Wikipedia, the free encyclopedia

Quadraphonic sound uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are (wholly or in part) independent of each other. Quadraphonic audio was one of the earliest consumer offerings in surround sound. It was a commercial failure due to many technical problems that were solved too late to save the technology from disaster. The format was more expensive than stereo, required extra speakers, and suffered from lack of a standard format for LP records. The rise of home theater products in the late 1980s and early 1990s brought multi-channel recording formats back to the forefront, although in a completely different and perhaps unexpected form. Quite a few quadraphonic recordings were made before its demise, and some of these recordings were later reissued on CD in Dolby Surround.

Contents 1 History 2 Formats 2.1 Discrete: 2.1.1 CD-4 (Compatible Discrete 4) / Quadradisc 2.1.2 UD-4 / UMX 2.1.3 Q4 2.1.4 Quad-8 / Quadraphonic 8-Track 2.2 Matrix: 2.2.1 SQ / Stereo Quadraphonic 2.2.2 QS / Quadraphonic Stereo 2.2.3 EV / Stereo-4 2.2.4 DY / Dynaquad 2.2.5 Matrix H 2.2.6 Hafler circuit 3 References 4 See also 5 External links

Introduced to the American market in September 1970 as the Quad-8 or Quadraphonic 8-Track, "Quad" (as it became known) didn't remain restricted to the discrete channel format used in the Quad-8. It appeared in several different and largely incompatible formats on different media. Quadraphonic audio could be obtained from vinyl records, eight track tapes, and reel-to-reel tapes.

Quadraphonic audio on vinyl records was problematic because some systems were based on discrete sound channels (allowing for full separation of the four original recorded channels, albeit with restricted high-frequency response and reduced record life), while others were matrix encoded into two tracks that would play back in stereo on two-channel audio equipment (so-called 'compatible' quadraphonic).

There were some experiments done with radio broadcasts (i.e. a Cliff Richard concert by the BBC), but they were short-lived. One of the longest lived radio broadcasters was WQSR-FM "Quad 102 1/2" in Sarasota, Florida. Through most of the 1970s this station broadcast a signal which could be tuned as two separate stations with conventional stereo receivers. In addition, San Francisco classical music station KKHI broadcast the San Francisco Opera in 'compatible' (that is, matrix encoded) quadraphonic format during the 1970s.

As its name suggests, with discrete formats the four channels are passed through a four-channel transmission medium and presented to four speakers.

Compatible Discrete 4 (CD-4) or Quadradisc (not to be confused with compact disc) 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; JVC; Nonesuch; RCA; Reprise and Warner.

This format was less popular than others because of incompatibility, poor longevity, and strict setup requirements.

The quadraphonic music was encoded with baseband sum and ultrasonic phase-modulated subcarrier difference signals (encoded in the 18 to 50 kHz range) similar in concept to the technique used in FM stereo, on the standard stereo grooves of vinyl, which also had the undesirable side-effect of limiting the high frequency audio response to 15 kHz with a 16 kHz 'pilot' tone. 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.

Channel	Left Front	Right Front	Left Back	Right Back
Normal Frequency Left	1	0	1	0
Normal Frequency Right	0	1	0	1
High-Frequency Left	1	0	-1	0
High-Frequency Right	0	1	0	-1

Although the format itself failed, the improvements it engendered in "super vinyl" and mastering techniques spilled over into, and substantially improved, the production of conventional stereo LP records.

UD-4/UMX - Developed by Nippon/Columbia (Denon). This is a hybrid discrete/matrix system. Only 35 to 40 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 play back these recordings but, by adding a special cartridge and a UD-4 demodulator, two supplementary channels could be extracted and used to enhance directional resolution. UD-4 systems first encoded the four original channels into four new channels. Two of these new channels contained the original four channels, matrix encoded. The other two contained only band-limited localization information, and were encoded with subcarriers similar to the CD-4 system. UD-4 was less critical in its setup than CD-4 because the subcarriers did not have to carry frequencies as high as those in the CD-4 system.^[1]

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.

Quadraphonic 8-Track was a discrete 4-Channel Tape Cartridge system introduced by RCA in Sept. 1970 and called QUAD-8 (later shortened to just Q8).

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.

With matrix formats the four channels are converted (encoded) down to two channels. 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. This 4:2:4 process could not be accomplished without information loss. That is to say, the four channels at the end were not identical to the four with which one began.

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, Supraphon 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. SQ is an acronym for "Stereo Quadraphonic." 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 competing QS format, allowed the full bandwidth from 20 Hz to 20 kHz to be used, giving a much more "open" and detailed top end.

The early SQ decoders couldn't produce more than 3 db of separation from front to back. Early "Logic" circuits were introduced to enhance separation to 20 db, but provided poor performance, very noticeable gain-pumping and an unstable, 'swaying' soundfield. The SQ system also faced resistance from broadcasters, since while essentially a 2-channel system, and totally stereo-compatible, it could have substantial mono compatibility problems - which posed serious issues with monophonic radios & all televisions of the era.

By the time that the most advanced Logic System was introduced for SQ, the Tate Directional Enhancement System^[2] invented by Martin Willcocks, "quad" was already considered a failure. Initially the Tate DES chips were in short supply as the original run were committed for use in movie theaters in the first generation of Dolby matrix surround sound system for the first release of Star Wars. They were also used 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 an SQ mix, as the matrices used are somewhat similar, but directional cues will not be properly located. 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 stereo compatible, so there was no need to create different versions of it)

SQ Encoding Matrix	Left Front	Right Front	Left Back	Right Back
Left Total	1.0	0.0	j0.7	k0.7
Right Total	0.0	1.0	k0.7	j0.7

j = + 90° phase-shift , k = - 90° phase-shift

Quadraphonic Stereo (sometimes referred to as RM or "Regular Matrix") 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, full mono compatibility, and though the adjacent speaker separation is only 3 dB, this symmetrical distribution produces more stable quadraphonic images.

The QS matrix system was employed to create the five-channel Quintaphonic Sound system used for premiere engagements of the 1975 movie Tommy. The left and right 35 mm magnetic soundtracks were QS-encoded to create four channels around the theater; the center mag track was assigned to the speaker behind the screen. The mag FX track was unused.

QS Encoding Matrix	Left Front	Right Front	Left Back	Right Back
Left Total	0.92	0.38	j0.92	j0.38
Right Total	0.38	0.92	k0.38	k0.92

j = + 90° phase-shift , k = - 90° phase-shift

EV - Developed by Electro Voice, also known as Stereo-4. Despite heavy promotion by RadioShack 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.

DY - Developed by Dynaco, also known as Dynaquad. The four speakers were arranged in a diamond (center-front, center-left, center-rear, center-right). The encoding was unusual in that it did not use 90 degree phase shifters. Very few items are encoded in this format, although it did inspire the "Hafler circuit" described below.

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 programmes were made for Radios 3 and 4, including a number of plays and some Promenade Concerts, while Radio 1 carried quadraphonic session recordings by various bands.^[3] The "H" has no meaning; they called the first matrix they assessed Matrix A, and then worked up the alphabet^[4][5]. The BBC later cooperated with the developers of Ambisonics to produce BBC/NRDC System HJ. This was based on tolerance zones designed to include modified versions of both Matrix H and the prototype two-channel encoding of Ambisonics known as System 45J. Subsequently the Nippon-Columbia UD-4 matrix was brought in to the standard, leading to the final UHJ name now associated with Ambisonics.

A passive Hafler circuit mimics the effect of "active matrix" decoding but without using costly electronics by recovering the ambient sound from a stereo recording. Named after its early proponent audio engineer David Hafler, the Hafler circuit approach exploits the high amount of stereo separation in the front speakers (also called crosstalk), and using the circuit typically reduces this stereo separation by only about 2 dB. The rear sound level in a live performance recorded in stereo is about 7 dB below the front, but clearly audible.

The rear ambient sounds such as applause, and even coughs from the audience, are generally received in "opposite phase" by the stereo microphones, while sound from the musicians is 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 between the live feeds from the stereo amplifier. Alternatively, one speaker can be used on its own. (See External links for a circuit diagram.)

1. ^ Cooper, Duane H.; Shiga, Takeo (June 1972). "Discrete-Matrix Multichannel Stereo". Journal of the Audio Engineering Society 20 (5): 346-360. 
2. ^ Willcocks, Martin E. G. (March 1974), "Directional Enhancement System for Quadraphonic Decoders". GB patent 1514162.
3. ^ Ratcliff, P.A.; Meares, D.J. (May 1977). "BBC Matrix H: Compatible system for broadcasting". Wireless World: 41-45. 
4. ^ Crompton, T.W.J. (November 1974). "The subjective performance of various quadraphonic matrix systems" (PDF). BBC Research Department Report 1974/29. 
5. ^ Gaskell, P.S.; Ratliff, P.A. (February 1977). "Quadraphony: Developments in Matrix H decoding" (PDF). BBC Research Department Report 1977/2. 

• Ambisonics
• Azimuth co-ordinator
• Four-channel compact disc digital audio
• Multitrack recording
• Surround sound

• Quadraphonic discography
• List of quadraphonic 8-tracks
• Quadraphonic - website honoring (and exploring) quadraphonic sound
• Learning about quadraphonics
• QuadraphonicQuad
• Collectible Quadraphonic Tapes
• Quadraphonic website by Wendy Carlos
• Hafler circuit
• Dolby surround