arsclist Transfer of multiple copies, was: Full 3-D mapping of groove?

["Doug Pomeroy" <pomeroyaudio@xxxxxxx>]

> Date: Fri, 6 Dec 2002 13:51:17 EST
> From: Mwcpc6@xxxxxxx
> Subject: Re: arsclist ELP Laser Turntable; Full 3-D mapping of groove?
>
> In a message dated 12/05/2002 7:56:26 PM Eastern Standard Time,
> smolians@xxxxxxxxx writes:
>
>>
>>  The problem here is that the waveforms won't be exact from copy to copy.
>> No
>>  record is exactly on center, and it's not likely that each copy will have
>>  the needle start playing from the identical spot.
>>
>>  Steve Smolian
> The idea of the mathematical correlation function is that it aligns the data
> so identical components match.  This should be possible to within a
> wavelength of the highest frequency present, on a millisecond time scale.  It
> might even be that the high frequency noise components of the master, being
> the same on all copies, would act as a clock signal for the process,
> completely eliminating variations in reproduction speed.
>
> Mike Csontos

In theory (best of all possible worlds), the audio combined from two
pefectly syncronized transfers of two different copies of the same
recording, will exhibit a 3 dB improvement in signal-to-noise ratio.  The
first problem, is syncronization, which must be exact. This has meant that
all the source discs be must transferred *simultaneously* (getting several
turntable platters to rotate in perfect sync is not a big problem).  Even
so, there would be sight timing differences, such as presented by off-center
pressings, which Steve mentioned.

It is gratifying to learn that CEDAR is thinking about this subject. It
seems to me their existing Azimuth Corrector is actually part of the
solution, as it can correct very small timing errors between two sources;
what's needed is a much more powerful processor to deal with larger
corrections over time.

Such a processor could sync transfers made at different times and on
various turntables, greatly simplifying the process and increasing the
potential usefulness of this technique. (Application of CEDAR noise-removal
processing to the various source transfers, before syncronization, would no
doubt contribute to optimum results.)

The theory also states each doubling of the number of sources improves the
s/n by another 3 dB.  So, *four* copies of the same recording could produce
a whopping 6 dB improvement!  Finding four different copies of the same
record is not impossible to imagine, in some cases. (Pull out all your
copies of those King Oliver Gennetts!)  And, if they didn't all have to be
transferred simultaneously, this technique could prove to be useful.
Extending the theory, we could expect to see a s/n improvement in the range
of 9 dB (!), if we could syncronize *eight* different copies of the same
recording; but, obviously, this begins to get rather unrealistic.

Doug Pomeroy   pomeroyaudio@xxxxxxx
Audio Restoration & Remastering Services
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