The "Compatible Discrete/CD-4" process was invented by JVC in 1969 and was an attempt to encode records with a comparable amount of four channel stereo separation only reel to reel tape was capable of (at the time) in its full glory.
"Quadradiscs", as they were called (JVC having patented the tech and RCA owning the name), were anything BUT "compatible": they
couldn't be played with a regular stylus; as the records were cut with deeper and back-walled vertical grooves containing out-of-phase rear-channel information. These required a "Shibata" ultrasonic frequency cartridge equipped with a four-edged diamond tip needle. The playback of these also required a tracking weight of between 3-5g (hence, the rise of direct drive turntables coinciding with quad...the belt drives would not have had sufficient torque).
Next, the cables from the tonearm had to connect to an outboard demodulator (if the receiver was a low-budget model and lacked the built-in circuitry) before the demodulator fed the four-channel preamplifier of the power unit. The demodulator would "decode" the electrical impulses from the cartridge and separate them into four signals; based on a similar principle to how FM stereo is decoded using an adjacent-channel subcarrier at an ultrasonic frequency (at 19khz and 38khz: the 19khz suggesting a multiplex signal is being transmitted, and the 38khz providing the linear separation between the channel info). [
THIS is the frequency response figure the vinyl cult loves to throw out there...regarding this totally ABSURDIST belief about the "miraculous" specs. of vinyl playback. IF YOU ARE NOT PLAYING 4-CHANNEL-ENCODED DISCS FROM 1973 WITH A SHIBATA STYLUS...THE 30K+ RESPONSE FIGURES ARE
MEANINGLESS!
. Records have no usable treble beyond 11k at the outer rim and it drops-off steadily to 9k by mid-point. Otherwise: the surface noise would be so loud and the high frequencies would sound like fingernails grating a chalkboard!].
These weren't around for long (circa: 1971-1975). Not everything was mixed in all-out/"Discrete" 4-chan. and, the combination of expense as well as the bad (global) economy of the '70s did not foster consumer faith in it. People had already overhauled their stereo systems around 1968 when transistors replaced tubes big-time...just a couple years' later they (probably) weren't interested in "upgrading"
again and at double the cost.
