Viridian...I agree that it is astonishing that a mechanical media like a vinyl LP can sound so good. With some dynamic equalization (instead of the fixed RIAA curve) it can be as quiet as a CD, and with reduced distortion. (This was the DBX LP system, which I once had).
I believe that the CD4 system used a carrier with frequency modulation above 20 KHz. Because it was FM an undistorted waveform was not necessary. It was intended that the rear channels have full bandwidth capability (20 to 20K) so the cartridge had to work up to 40 KHz. In fact, although CD4 was a flop, phono cartridge design was greatly improved as a result of CD4.
I believe that the CD4 system used a carrier with frequency modulation above 20 KHz. Because it was FM an undistorted waveform was not necessary. It was intended that the rear channels have full bandwidth capability (20 to 20K) so the cartridge had to work up to 40 KHz. In fact, although CD4 was a flop, phono cartridge design was greatly improved as a result of CD4.