CD-4 Quadradisc

CD-4, or Compatible Discrete 4-Channel, recordings contain a sum signal and a difference signal on each wall of the LP record groove.  To decode these signals, you need a CD-4 disc demodulator.  The demodulator uses the sum and difference signals on each groove wall to reconstruct the left front and back and right front and back quadraphonic speaker signals.  The technique is the same as used in FM stereo.

The difference signals ride on a very high frequency carrier.  As a result, to play CD-4 records you must use a phono cartridge that meets many requirements not satisfied by the typical stereo cartridge.

Fourth, total per channel load capacitance of the tonearm wiring and of the phono cables from the turntable to the CD-4 demodulator should not exceed 100 picofarads, and the lower the better.  In addition to using low capacitance phono cable, make it as short as possible.  And plug the cable directly into the demodulator, not through an external pickup switch box, which adds to the total capacitance.

The sum signal on each record groove is what makes CD-4 records compatible with two-channel systems.  If you do not have a CD-4 demodulator or high frequency phono cartridge, you'll still hear all the music the recording artist and engineer intended.

Last updated: October 13, 2001