Thanks Ted, 

I'd thought I'd read  Peter Copeland's BL paper thoroughly enough but
must have missed where he talks about this.  I  thought of the cake
stand idea but then thought a conventional turntable with a high
sample rate readout of time base (platter rotational angle at any
given moment) would be more practical as it seems mechanically easier
and requires the least mechanical mods to the turntable. Even though
the turntable's speed mightnt be entirely accurate it seems possible
to  correct it in post using the turntable's time base information
once the files are digitised using a Plangent bias type process.  

I'll try and chase up Hicks'  paper.


----- Original Message -----
From: "Association for Recorded Sound Discussion List"
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To:<[log in to unmask]>
Sent:Sun, 20 Dec 2020 06:58:42 +0000
Subject:Re: [ARSCLIST] Noise reduction on mono records using two
separate coherent sources

 This was a favourite thought experiment of Peter Copeland, late 
 conservation manager at the British Library National Sound Archive.
 idea was the "cake stand", where two platters were mounted in the
 spindle. Even with this (presumably) rigid coupling between the two 
 transfers, warpage, off centre pressings and differing pickup 
 compliances would throw synchronism off enough to defeat the object
 the exercise. Christopher Hicks of CEDAR did his doctoral thesis on
 problem as well, and managed by some cunning DSP to hold five copies
 the same recording in sync long enough for the theoretical benefit to

 confirmed. As things stand, though, as a practical technique it's
 a non-starter. One day, perhaps...

 On 20/12/2020 05:20, Tim Gillett wrote:
 > Hi all,
 > I've  familiar with the principle of summing two audio recordings
 > the same programme where the wanted programmes are time coherent
 > the unwanted background noises arent, making it possible in theory
 > realize a 3db reduction of the background noise. I've used it  on
 > cassette and  1/4 track "stereo" recordings which are actually
 > mono, although time alignment can be a little tricky and an
 > tool can really help.
 > Earlier 78 RPM recordings  are understandably noisy especially as
 > believe was customary, the original metal parts were usually
 > for cost reasons  so all transfer engineers have to work with may
 > the best shellac consumer pressings that have survived.
 >  The other day while browsing I chanced upon a seemingly mint
 > condition 10"  78 shellac  record of  Eileen Joyce performing
 > "Berceuse" in 1939.  Here's a modern CD release of it.
 > Quite noisy and limited bandwidth, even for 1939 I thought.   I
 > cleaned and transferred the disc I'd found and after declicking
 > compared the sound to the version linked to. The two versions
 > close. Signal to noise was about the same.
 > I believe that compared to vinyl, shellac was  a relatively noise
 > medium so it occured to me that assuming the stamper had less noise
 > than the shellac copies, it should be possible to time align the
 > from the two discs, sum to mono and  yield a potential background
 > noise reduction of 3db. Not huge but with an already noisy
 > not to be sneezed at!
 > So far I've not had much success. I'm having problems trying to
 > accurately time align my disc transfer with the  commercial
 > I can get them within maybe a few milliseconds but it's not enough.
 > The two versions drift in and out of sync causing comb filtering.
 >  My next step might be to find another mint disc of the same
 > performance and make my own transfer of both on the same gear under
 > the same conditions so at least there is a fighting chance of an
 > accurate  alignment. Maybe a better turntable with more precise
 > regulation?
 >  Has anyone tried this technique with 78 RPM shellac records or
 > any comments?
 > Cheers Tim.
 > -------------------------
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