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LP Equalisation Curves used by US Columbia
I am the Technical Manager at the British Library National Sound
Archive. My work involves studying "industrial archaeology" to
determine how old recordings were *meant* to be reproduced. Normally,
it is a simple matter to establish which equalisation was used when a
company started making LPs; but I have found innumerable examples when
companies hid the change to what later became the International
Standard, "RIAA". I am seeking a solution to this problem with U.S.
Columbia. (Please forgive my pedantry calling it that; here in Britain
the Columbia tradename was owned by EMI at the time, and had almost
totally different repertoire - and equalisation!). Herewith a rather
long explanation of my problem, for which I apologise.
Since the 1920s, US Columbia had done a great deal of mastering
for syndicated broadcasts, so it had used NAB characteristics since late
1941, which became used for microgroove besides their own
characteristics in 1948. (It is possible the deficiencies of the former
showed the need for the latter). When they carried out mastering for
other logos, they were often NAB. Unfortunately I do not know a way of
distinguishing them, although after about 1950 (when variable-pitch
grooving was used for Columbia's own LPs), the NAB-equalised LPs always
seem to be cut at constant pitch. Can anybody help - were there
different number-blocks, for example?
US Columbia seems to have allocated consecutive numbers for most
of their microgroove masters, starting from 200 in early 1948. By
1954, when RIAA seems to have been adopted throughout America, they
had reached about 20000 (and then appear to have jumped to 30000).
The prefixes include TV (ten-inch sides), XTV or XLP (twelve-inch),
and ZLP and ZSP (seven-inch 33s and 45s).
US Columbia's characteristic was, in engineering terms, a good
one, and does not seem to have changed with time. It was so
well-founded that by 1952 constructional articles, texts, and
preamplifiers were calling it simply "The LP Curve" without mentioning
US Columbia's name at all, which is rather misleading - especially as
the acronym "LP" was, at the time, a registered trademark in America.
However, I have yet to see an official statement of the timeconstants
involved. They seem to have been 100, 398, and 1590 microseconds. I
have worked this out from circuits and curve-fitting - can anyone back
I do not know precisely when the change to RIAA took place; the
differences between US Columbia and RIAA are not conspicuous to the
ear. Unfortunately, US Columbia itself maintained a public silence. I
have written elsewhere about the results of listening-tests comparing
the same subject-matter to resolve such anomalies, but finding two
copies of the same performance on LPs with different equalisation is
practically impossible on this side of the Atlantic.
Another difficulty lies in understanding the matrix-number
suffixes, which do not follow any system I know. I conjecture that
when the subject-matter remained the same, the "take number" remained
the same; but if re-mastering proved necessary, the letter following
the take-number incremented. (Again, can anyone confirm this?)
To narrow the difficulty, I have used LPs mastered by US Columbia
and issued under the following US logos: "Vox", "Westminster" and
"Haydn Society." These logos did not maintain the aforesaid "public
silence" about their change to RIAA. If the information on their
sleeves is correct, and assuming US Columbia changed at the same time
and also that it numbered its masters consecutively, then the
changeover seems to have been between matrixes XTV19724-1A and
If anyone can confirm or deny any of this, I would be very
grateful, and I hope to reciprocate somehow.
British Library National Sound Archive,
96 Euston Road,
LONDON NW1 2DB.
tel: 0207 412 7420