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- May 9, 2021
Hi Doug and all Sandpaper fans!Sandpaper distortion is actually the carrier detection circuit switching on and off as it gains and loses the carriers in rapid succession. It is not a function of that actual noise coming from the groove. It is a function of the demodulation process if it's not going right.
The "breaking pencils" or "explosions" aspect only happens if the CD-4 system is not set up correctly. Scratches or dirt sound no different from two channel records in my system. As I have stated elsewhere, I have heard the various CD-4 distortions and actually did have some of them in my system when I re-entered the CD-4 world many years ago, now, but they were corrected, mainly through tracking adjustments.
You're right with Sandpaper, the carrier goes out of limits. Even if there is a small buffer for small dropouts, if the carrier is always pending around the lower limit we will get the sandpaper.
Found a good example at the Doobie Brothers - Stampede.
I recorded all at the same level, only adjusting the horizontal angel to get the optimum.
Pic 1 shows the 30kHz at track 2 (or any other) beforre the the music and at the last track 5. Of course the switch (carrier sense = matrix on) got problems to handle that.
Pic 2 With Audacities's equalizer I added 8dB for the carrier to bring em up to normal volumen - than it plays well without any distortions.
Pic 3 I clip off the carrier in both recs at 20kHz to get the normal sound we hear. You see, there is is no difference in the volumen between a formerly low or high carrier in the sound.
Roberta Flack Suzanne is also an example: they reduced slowly the carrier from the 6th minute till end. so I added the 30kHz 1dB after 7min, 8min and 9minutes to keep em upright = everything OK.