Scott Dorsey wrote:
Adrian Tuddenham wrote:
That's interesting. We don't get many Red Seals this side of the pond,
but it would be helpful if you could let me know the turnover
frequencies (or time constants). There have been several attempts to
draw up definitive tables of turnovers for different makes at different
times, but they always seem to be incomplete, in dispute or inaccurate.
It's a two pole filter. F1 is specified at 500 Hz, F2 is 1590 Hz and
set for 13dB at 10 Khz. Maybe.
Even wackier is the Columbia stuff! Columbia used a three-pole filter
like the modern RIAA curve on some of their later 78 and early LP pressings.
F1 at 100 Hz, F2 and 500 Hz, F3 at 1590 Hz, and something like 16dB boost
at 10 Khz.
None of these numbers are guaranteed, and the might be totally wrong. But
they aren't any worse than the ones in the McIntosh preamp book.
Thanks for that. Now you have reminded me, I'm think I remember reading
something about those turnovers some years ago. My recollection is that
they didn't apply to pre-WWII recordings, so there was no need to
remember them.
There are a couple of strange curves that turn up in the U.K. from time
to time. Early recordings by P.G.A.H. Voigt were approximately constant
velocity up to at least 1Kc/s; but the microphone response has to be
taken into account too. Luckily he published an account of his
experiments in Wireless World.
The B.B.C. used 2dB per octave for their 'Type D' transcriptions. That
was a particularly difficult curve to synthesise in an analogue system,
but I eventually succeeded with a cascade of three RC networks. The
U.K. National Sound Archive used my circuit, as did Ted Kendall's
'Mousetrap' processor - then one day the B.B.C. rang up and asked if
they could also use it, as they didn't have any original playback
equipment left in working order!
--
~ Adrian Tuddenham ~
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