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From: Patent Tactics, George Brock-Nannestad Background. About 1980 I set about to compare several sets of Edwin Fischer's recording with Karl Boehm conducting the Saxon State Orchestra in Beethoven: Concerto no. 5 Op. 73 that I had been fortunate to obtain previously. German wartime pressings were easy to find in Denmark at the time and generally under- priced. According to my notes made at the time, first of all I noted that all published sides except side 1 were made in the "Transfer Room", i.e. they were re-recorded from an original master disc to the side used in manufacture. Secondly I found four supplementary "takes" (really a misnomer in the case of re-recording, unless the particular original was really a different take) that had not been identified in the authoritative discography at the time, Henning Smidth Olesen: "Edwin Fischer A Discography", Danmarks Biblioteksskole Copenhagen 1974. There may well be better discographies available now. In distinguishing between the various "takes" I measured the outside diameter of the recorded area and the width of the recorded area. This was a first approach to using the physical layout of the recording to document an individual copy of a record in order to compare it to other records having the same catalogue number. This approach was not unique at the time - I certainly had collector colleagues who did similar things. And there is no doubt that sometimes you need to go into such details in order to distinguish sides. There is a need to find identifiers. The recording lathe. In 1997 I digested a lot of material I had collected about EMI practices and published it as "The EMI recording machines, in particular in the 1930s and 40s", The Historic Record & AV Collector No. 43, pp. 33-38, April 1997. In the article, I noted that the four groove pitches obtainable from Columbia- derived recording equipment were all different from the four groove pitches obtainable from Gramophone-Company-derived equipment, and that one might then distingiuish unambiguously between the two types in a particular recording session. Since then I have been increasingly occupied with the actual mark left on a recording by a particular type of recording lathe - a part of the so-called ancillary or secondary information carried by a mechanical sound recording (in which the recorded sound is the desired or primary information). The reason is that there are frequent cases where it is uncertain what went on during recording, what was the equipment, and settling the issue of equipment may be the clue to a better understanding of a recording session and its placement geographically or in time. A recording lathe might be identified at a location where it was not expected to have been. We do not have recording ledgers for everything. The most important mark is certainly the groove pitch - the number of revolutions needed for the cutting stylus to travel one inch or the number of complete groove-land cycles you pass on a linear inch along a radius. The groove pitch is set by a gearbox, and you really need major conversions to go outside the normal selection in a particular recording lathe. For puzzle or race-track records you needed a groove pitch that was for instance 3 or 6 times as steep. The recorded area information I have mentioned above, but that is not per se an identifier of a particular recording lathe type. Another important mark is the rumble, in particular the vertical rumble (from a lateral recording), because that is frequently related to teeth on cogwheels not meshing properly, and cogwheels are individual to a particular model of recording lathe. Also, the gear ratio between the governor shaft and the turntable may be measured in the rumble. Recent developments I have of lately increasingly measured the groove pitch on records that I inspect, and I consider that information to be just as essential as the matrix number or other markings at various clock-face locations on a record. And, in contrast to the markings that may be entered manually subsequent to inspection into the meta-data of a recording, nobody to my knowledge is concerned with the groove pitch. But that goes for the recorded area information mentioned above as well. So much essential discographical work is dependent on the possibility of comparing physical record sides that we must consider mass transfer of mechanical records into a digital format to be deficient, unless these types of information are made available too. The same goes for mass destruction of apparently identical recordings (duplicates) - unless they have been compared to this detail, information will have been destroyed. The groove pitch is measured in grooves per inch (gpi) and so is the screen ruling or screen frequency in half-tone printing (but called lpi in this trade). For this reason I am using an adaptation of an implement used in the graphics arts for the measurements. It will only work simply if the record does not display twinning, which a surprising number of early recordings did. Twinning is caused by a stick-slip phenomenon: the movement across the record was not entirely even, but stopped, until the pressure from the transport mechanism was sufficient to overcome the static friction, and then the cycle started again. Good lubricaton was one way of avoiding the problem, but it did not always work. Certain recording lathes had special provisions to completely avoid the problem. And I warn you: some lathes I know use 96 gpi and some others use 97 gpi (at the setting just below 100 gpi), and that requires quite some precision in working. Another way would be to have a precise linear travel indicator on your tonearm and a revolutions counter for your turntable. The groove pitch information may possibly not be directly measurable in the photographs that form part of the new process called VisualAudio developed in Switzerland, because that relies on a lens forming an image of a record side on a film (which is later scanned in order to convert the image to a linear sound file), and unless that lens is designed to preserve linear distances in the image formation, the groove pitch will vary from the rim and towards the centre. Only if some calibration is introduced will it be possible to enable the scan to detect the linear frequency of the groove image along a radius. Now, I would like to see if the groove pitch information could be a shortcut to distinguishing beetween VTMC recordings that were repeats of earlier recordings without change of catalogue number or matrix no. They might have changed their recording lathe. And the approach could conceivably also be used to check the origin of reissues of smaller label recordings by larger labels. However, the approach does not work for variable pitch recordings, such as Fuellschrift or Variable Micrograde. If anybody would like to use the groove pitch comparison approach, then please note that you read about it first here (or in 1997). Unless, of course, if anybody has knowledge about prior use of the approach, then I would like to hear about it, and I will give due credit in future communications. I hope that you have been inspired by the above. George.