-----Original Message-----
From Eric Jacobs: "Weren't all those math formulas and standards the basis
of the RCA test record?"

In terms of public dissemination, the test record predates all of them that
I'm aware of although no doubt there was some sort of internal documentation
at RCA. 

The 1953 standard specified a series of 23 frequencies ranging from 30 to
15k. as is found on the test record. This was only later described as the
3180, 318 and 75 microsecond time constants so the RCA test record may well
have been the basis and not the other way around. Again it should be the
basis of any attempt at accurate reproduction simply because it was what
everybody trimmed the response of their cutting systems to match. How right
or wrong the RCA test record is doesn't matter.

There was a revision in the '70s that rolled off subsonics but to the best
of my knowledge this was never actually implemented in a cutting system.

Bob Olhsson Audio Mastery, Nashville TN
Mastering, Audio for Picture, Mix Evaluation and Quality Control Over 40
years making people sound better than they ever imagined!