Quadraphonic sound

Quadraphonic sound uses four channels in which speakers are positioned at all four corners of the listening space, reproducing signals that are independent of each other. "Quad", in its original form, was a commercial failure, and the LP formats were plagued with technical problems that were solved too late to save the system from a consumer point of view. The format was more expensive and required extra speakers, which became a decorating problem. It also suffered from lack of a standard format for LP records.
As its name suggests, with discrete formats the four channels are passed through a four-channel transmission medium and presented to four speakers.
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 (encoded in the 18 to 30 kHz range) on the standard stereo grooves of vinyl which also had the undesirable side-effect of limiting the high frequency response to 15 kHz at the most. To play back the record, a special high-frequency cartridge andstylus 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

Quad-8 / Quadraphonic 8-Track
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.