Analog Quadraphonic Formats
Quadraphonic sound uses four channels in which speakers are positioned at all Four Corners of the listening space.
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
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
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
- 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
Quad-8 / Quadraphonic 8-Track
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
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
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.
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.
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
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
EV / Stereo-4
- 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.
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
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
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.