I feel the one turntable approach could be better. Then the hardware
and adjustments would be the same down to the stylus and setup. If
changes were needed for say a slightly different stylus, that could be
accommodated.
I see it as really an information game, regarding errors. Errors are
OK so long as that error information is captured and can be used to
correct the errors, within the system limits. There are potentially
multiple errors so each type of error would need to be captured and
fed into an appropriate feedback loop.
1. A turntable with the necessary short and long term speed stability
may not be practical. Capturing the turntable's *speed error
information* synced to each audio capture seems a far better way to
go, if not the only practical way. Software would apply the time base
correction to the high sample rate audio file of each disc.
2. Off centre disc error could be captured, perhaps via an optical
sensor.
3. Even the timing error caused by a slightly buckled disc could be
captured and translated into speed and pitch error, via capturing the
vertical displacements of the tone arm. Obviously a very buckled disc
would be ruled out as a candidate.
4. Then when each of those error types had been corrected as well as
possible we still may have timing errors between each disc side which
might best be corrected (as well as is possible) with software
comparing the two disc audio files and measuring the remaining timing
difference error and attempt to correct it. Software could be based on
a standard tape azimuth corrector, as per CEDAR, RX etc.
As with any audio restoration software, the order of use can be
critical. So we dont HPF before we declick etc. Maybe dont even
declick until all the timing corrections have been made.
Ted Kendall says that some years ago Christopher Hicks managed to
successfully sync up 5 discs. So it's possible to do it, on more
than just two discs and that was just one project. Compare the
long timeframe and setbacks along the way it took to develop decent
quality commercial videotape recording. As here, successful videotape
recording and playback very much revolved around accurate timebase, on
multiple fronts. Back in 1956, they finally achieved close to the
then broadcast quality video record and playback, but without the huge
benefits we now have of today's technology. It was even totally
valve technology.
Maybe sound quality aside, most consumers arent much interested in
purchasing for example the recorded performances of the late 1920's
until around 1950. Maybe the reason this sort of thing hasnt been
developed to a high level is because there's mostly not enough income
to be generated from the improved audio.
Tim
----- Original Message -----
From: "Association for Recorded Sound Discussion List"
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To:<[log in to unmask]>
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Sent:Mon, 21 Dec 2020 18:35:59 -0500
Subject:Re: [ARSCLIST] Noise reduction on mono records using two
separate coherent sources
So my humble idea FWIW would be to have 2 identical turntables, same
tonearm, cart and stylus, TF, etc. both driven by a common source;
some sort of servo controller that would output identical power,
timing, locking, etc. to both tables. You’ve now theoretically got
rid of most of those variations and you’re left with just the disc
anomalies. They don’t necessarily need to be run exactly
simultaneously, but the time base would be common and sync could be
corrected (?). If I have the idea correct, this is different from the
cake platter concept.
Others seem to be suggesting a sort of M/S processing which, even if
successful on one disc, I would never even bother attempting with 2
copies.
Jeff
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