[78-L] Fake stereo

[Doug Pomeroy]

Mike,

Gary Galo's article in the ARSC Journal of Spring 2010 describes the two types of digital filters
(IIR and FIR) and notes that only the IIR properly matches the phase response of an analog filter.
Gary also gave a talk at the 2009 ARSC conferences about this.  The Tracer Technologies DC7
software includes an IIR filter which duplicates the analog phase response, and I wouldn't call this
program expensive.

Someone mentioned the method of imposing a 90 degree phase shift between the channels to
create phony stereo.  I remember Columbia used this technique for a while.

And no one has mentioned engineer Robert Parker, who produced many phony stereo jazz reissues.
He used Robert Orban's equalizer which is truly mono compatible - if the channels were combined, 
nothing was added or lost.  (Unfortunately, the reverb he added reverb could not be eliminated.)

Doug Pomeroy
audiofixer at verizon.net

> Message: 2
> Date: Sun, 03 Mar 2013 13:46:15 -0700
> From: "Michael Biel" <mbiel at mbiel.com>
> Subject: Re: [78-L] Fake stereo
> To: "78-L Mail List" <78-l at klickitat.78online.com>
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> From: "Milan Milovanovic" <milanpmilovanovic4 at gmail.com>
>> Michael, are there consequences regarding eq while doing it
>> (digitally) on flat 78rpm monaural transfers? What really we
>> can expect in that matter? Cancellation of some frequencies?
>> Other irregularities?  Thank you,  Milan
> 
> What was being specifically discussed in the presentation was "undoing"
> the pre-emphasis curve where the goal is a transparent unnoticeable
> restoration back to the original.  Since the analog pre-emphasis had
> filters would do some phase bending, that phase change would also have
> to be undone, which does happen in the analog domain but digital
> filtering doesn't -- unless it is purposefully built into the program,
> which is expensive.  The phase-sensitive Audiophools notice the change
> in the soundstage.  Since we are not "undoing" any eq on most 78s --
> although with the research of Nick Bergh we are finding more about what
> the Victor engineers were doing with those filter settings shown on the
> victor ledgers (and are being ignored by the Victor Project discograpy)
> -- I am not sure whether any of us can really tell the difference
> between analog and digital tone controls.  Settings do not change things
> so much as to affect cancellations of frequencies.  I think.  But I
> still rather do these things analog.
> 
> Mike Biel  mbiel at mbiel.com