Paul Stamler wrote:
Hi folks:
Here's a weird one, for those interested in 78s....
[...]
you can see that in fact it's a tone which alternates pitch between high and
low, once per revolution. (It may help to click on the image for a cleaner
view.) At the start of the recording, the lower pitch is at about 20.5kHz,
while the upper pitch is above the Nyquist frequency of this 44.1k sample
rate and so is not recorded. By the end of the tune, the high pitch is about
12kHz and the low is about 10kHz, both quite audible despite the record's
surface noise.
It often occurs very noticeably at the end of 8" 'Broadcast" records
made by the UK branch of the Vocalian Co. For a long while I thought it
was because the Marconi recording process, which is what they used,
might have been equipped with a long whippy cutting tool which began to
chatter at slow surface speeds near the end of the disc.
Some time ago, I discussed this matter with two disc cutting engineers,
the late Peter Copeland and (the still very much alive) Sean Davies.
They came to the conclusion that it was mainly due to the wax cooling on
the lathe turntable during the cutting session (no nitrate in those
days).
It would be useful to keep a note of these examples and try to relate
them back to the recording conditions. Were any know to occur during
summer or were they all recorded in winter? Were they more common on
location and/or in a recording van, where the air temperature would be
lower or the wax ovens less effective?
An interesting project for anyone with enough time to spare.
--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk