I'm about to venture into what can be a touchy area for quad enthusiasts. CD-4 (or Compatible Discrete 4) did not rely on any matrix system to extract it's 4-channel information. It used a carrier driven signal invented by JVC. The sum of the front and rear signals are combined on each wall of the record grove, then a very high frequency carrier level is applied which contains the difference signal. This signal starts at 30,000 cycles and extends up near 50,000 cycles. When played on a regular stereo, these discs sound normal (hence compatible), but to hear the quad separation, the signal must be demodulated. If setup correctly, it is a viable format that out performs matrixed recordings and can still be enjoyed today. If it's setup poorly, it can sound brittle and distorted earning the name "sandpaper quad."
Got a dog??? Play a CD-4 album really slow. See how high you can get those ears up!
What you need...
a CD-4 Cartridge with a Shibata tip stylus,
a CD-4 Demodulator,
and a killer quad system!
THIS JUST IN!
CD-4 is both loved and hated by quaddies. It takes a lot of patience, experimenting, hunting, tweaking, and did I mention patience? I finally got it! A post on a Obbop's quad discussion group from "the quadfather" said to try an Audio Technica Trackmaster 8 or an AT331LP cartridge. These are line contact stylus cartridges and are both P-mount. They are only rated to 30,000 cycles, but that has to be low. These babies really sound fantastic, even on worn CD-4 albums. They are around or below $50.00 and work best on a linear turntable. I have to say that CD-4 can blow away matrix recordings if they are in good shape. CD-4 gives true stereo sound fields in the rear channels or between any channel, something that matrix recordings cannot do. If you have been trying unsuccessfully to listen to CD-4, this might do the trick for you.
Here's Obbop's take on why he dislikes CD-4.
Vinyl has a limited ability to 'hold' the high-frequency carrier signals.
The high-freq signals in vinyl are subject to wear.
Only new, untouched by a standard stylus LPs, are assured of having the high
frequency grooves in the vinyl.
Not compatible with any other quad system.
Noise and distortion are common problems.
Poor carrier signal lock-up can cause audible distortion.
A cartridge/stylus combo capable of reproducing 25-45Khz is required.
Cartridge tracking adjustments must be near perfect.
Some turntable tone arms are incompatible with CD-4.
Anti-skating adjustments can be crucial to proper playback.
Some of the earlier records were inferior, wearing quickly.
Can only be recorded onto a 4-channel tape recorder.
Turntable leads, in some cases, need to be low impedance for CD-4 to work right.
Channel separation of 30-35db max can be matched by a good matrix decoder.
I think CD-4 has an "artificial" sound.
The demodulator needs to be manually 'aligned' via 2 to 3 adjusters.
Because JVC, CD-4's creator, never paid me to say something nice.
Finally, a letter I received from Helge Skjeveland.
BTW, remember CD-4? That was a real joke. The Shibata styli wore out quickly, and the HF FM component on the LP wore out too, so one got "sandpaper" quad very quickly. The first dozen or so play-throughs were glorious, then garbage set in. This was because the cartridge compliance wasn't high enough to follow the high-velocity ultrasonic track precisely, and wore out the HF info there fast. Then, the CD-4 matrix that was supposed to extract the four discrete channels couldn't reconstitute it accurately. That problem never affected the phase matrices SQ and QS, but they traded discreteness for durability.
And now some "Tab Tips"
Try cleaning your albums with a wet vacuum cleaning system like a Nitty Gritty Record Doctor. These are also available from Audio Advisor or Garage-a-Records, a good source for locating a quad stylus replacement or turntable parts. Regular cleaning will decrease the wear on the vinyl and make it sound a whole lot better. This is true for all vinyl...stereo, matrix quad, or CD-4.
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