Tracing Predistortion in Quadraphonic CD-4 and UD-4?

[vladan3101]

The thread on my JAES paper on tracing distortion got a bit hijacked by some semantic discussions (https://www.lathetrolls.com/viewtopic.php?f=1&t=10062), so I am opening a new one.

The JAES editor just sent me a "Comment on... "type of paper where the author pointed out an oversight on my part (D. Cooper's "deskewing "solution being implemented by Nippon Electric per ref. [53], I wrote that it is not clear if it was ever commercialized).

But more importantly, he pointed to the paper T. Takagi, "UD-4: The System and Its Use," Studio Sound, vol. 17, no. 6, pp. 42-43 and 48 (1975 June, available at https://www.worldradiohistory.com/Archive-All-Audio/Archive-Studio-Sound/70s/Studio-Sound-1975-06.pdf) which showed that UD-4 appears to have used "de-tracing" predistortion regularly. He did not mention it, but the paper on CD-4 in the same issue by none other than J. Eargle (same link, pp. 44-46 and 48) describes a de-tracing used in CD-4 ("tracing correlator," in UD-4 they called it "tracing simulator ").

I was completely unaware of this, but my further research showed that one paper in JAES corroborated the claim (O. Isao, et al "Further Improvements in Discrete Four-Channel Disc System CD-4," J. Audio Eng. Soc., vol. 20, no. 5, pp. 361-369 (1972 June, https://www.aes.org/e-lib/browse.cfm?elib=2069). I could not find anything else in JAES and JASA journals.

In hindsight, given the high frequencies of the carrier signals for two additional channels, the tracing distortion effects in truly quadraphonic systems like UD-4 and CD-4 would have been very severe without some anti-tracing mechanism applied during the disk mastering. It is also possible that the CD-4 and UD-4 advocates did not want to emphasize that their systems required some form of "de-tracing" after all the bad publicity the "Dynagroove" received. Still, I don't recall this being discussed in technical and popular journals in the 1970s.

The JAES editor seems inclined to publish this comment, and if that happens, I will be asked to provide my response. I have no problem acknowledging the first mistake, but I am a bit uncomfortable about responding to this quadraphonic part.

Does anybody on the Forum have any experience with tracing simulators/correlators used on the CD-4 and UD-4 disks, or can point to some other reference on this?