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ARSCLIST  June 2012

ARSCLIST June 2012

Subject:

Re: multiple copies for surface noise reduction, was Re: audio from pictures

From:

Randy Riddle <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Fri, 22 Jun 2012 11:09:54 -0400

Content-Type:

text/plain

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text/plain (92 lines)

It would seem to me that if the sources were recorded in high
resolution that a computer algorithm could sync the signals,
shortening or lengthening minute sections of the audio so they would
match up.

On Fri, Jun 22, 2012 at 11:06 AM, Aaron Z Snyder <[log in to unmask]> wrote:
> These contributions from Ted Kendall and Doug Pomeroy have convinced me that
> all attempts at reconstructing "accidental stereo" from two
> simultaneously-recorded 78's with separate mic sources will be futile ---
> that is, unless someone can construct an algorithm to keep the separate
> sources in a continuously stable phase relationship. I've already looked at
> a couple of these reconstruction attempts and observed that even short-term
> phase stability is completely absent. The net result is pseudo stereo even
> if there's genuine spatial information shared between the two sources. I
> take no pleasure at all in coming to this conclusion, but that's reality.
>
> Aaron Z.
>
>> -----Original Message-----
>> From: Association for Recorded Sound Discussion List
>> [mailto:[log in to unmask]] On Behalf Of Doug Pomeroy
>> Sent: Friday, June 22, 2012 10:30 AM
>> To: [log in to unmask]
>> Subject: [ARSCLIST] multiple copies for surface noise reduction, was Re:
> audio
>> from pictures
>>
>> >
>> >> Date:    Wed, 20 Jun 2012 10:44:42 +0100
>> >> From:    Ted Kendall <[log in to unmask]>
>> >> Subject: Re: audio from pictures
>> >>
>> >> <<SNIP>>
>> >>
>> >> Chris Hicks of Cedar did his doctorate on just this question of
>> >> multiple copies. When the algorithm could be persuaded to work, the
>> >> results were much as you would expect - enhancement of the correlated
>> >> wanted signal and reduction of the random noise. Unfortunately,
>> >> pulling the recordings into good enough sync for artifacts to be
>> >> negligible was a frustrating and difficult business, even with
>> >> recordings made one after the other (by me, as it happens) on the
>> >> same kit on the same settings on the same afternoon, with meticulous
>> >> centring. The minute geometrical differences between different
>> >> laminated pressings were enough to throw things continually out of
>> >> register. The example produced, however, is a tantalising glimpse of
>> >> what might one day be possible.
>> >>
>> >> Whenever I do a master of the QHCF Decca of "Souvenirs", I use three
>> >> copies from the shelf - one for the very start, one for most of the
>> >> side and one for the last few turns where the others are afflicted
>> >> with "Decca scrunch".
>>
>> I gave a talk on this subject at the ARSC conference in Nashville in 1997.
>> Two perfectly synchronized copies would provide a theoretical signal-
> to-noise
>> improvement of 3 dB, four copies an improvement of 6 dB and eight copies
> an
>> improvement of 9 dB. The first problem is finding so many copies in E
> condition.
>>
>> But the bigger problem is how to achieve perfect synchronization.
>> John S Allen of the Boston Audio Society discusses this matter in an
> article he
>> wrote for the Spring 1990 issue of the ARSC Journal.  He says the accuracy
> of
>> sync must be "about ten microseconds (72 degrees of phase shift at 20
> kHz)".
>> No real-world turntable is stable enough to achieve this result on
> successive
>> plays, and I proposed a stack of tables all powered by a single motor for
> playing the
>> discs simultaneously, with use of digital delay lines to align the audio
> from them
>> after transferring.
>>
>> Discs which are even slightly out-of-round would need to be matched
> perfectly
>> with others of the same shape (not impossible, since these discs reflect
> the shape
>> of the metal stamper used to press them), and digital "azimuth correcting"
> software
>> might be used to help deal with alignment variables such as this.
>>
>> Doug Pomeroy
>> Audio Restoration & Mastering Services
>> Transfers of metal parts, lacquers,
>> shellac and vinyl discs & tapes.
>> 193 Baltic St
>> Brooklyn, NY 11201-6173
>> (718) 855-2650
>> [log in to unmask]

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