LP Equalisation Curves used by US Columbia

[Peter.Copeland@xxxxxxxxxx (Peter Copeland)]

     Dear All,
     
         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 
     me up?
         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 
     XTV19938-1C.
     
          If anyone can confirm or deny any of this, I would be very 
     grateful, and I hope to reciprocate somehow. 
     
     Peter Copeland
     Technical Manager
     British Library National Sound Archive, 
     96 Euston Road,
     LONDON NW1 2DB.
     email: peter.copeland@xxxxx
     tel: 0207 412 7420