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Re: [ARSCLIST] Dynamic-frequency Range

From: Patent Tactics, George Brock-Nannestad

Aaron Z. Znyder wrote

> .................
> Steven Barr, and later Don Cox, suggest determining the transfer functions
> of old recording apparati so that the resulting recordings can be
> de-convolved. That's what Thomas Stockham tried to do in the 1970s,
> primarily with recordings by Caruso. The results were fascinating,
> although
> the quality was quite variable. Among the basic problems were and are the
> following:
> 1) It is virtually impossible to get a truly accurate transfer function
> for
> an acoustical recording environment, since there is such an incredible
> number of variables, including the size of the horn, the acoustics of the
> recording room itself, and the distance from and angle to the horn of the
> performer(s). 
> 2) Add to this the fact that, even on a single-sided recording, a
> particular
> instrument's sound quality might vary due to actual physical movement of
> the
> performer, i.e. moving close to the horn for a solo, and then moving away
> to
> allow other soloists to be spotlighted. 
> In the end, human intervention and lots of guessing must be employed if
> the
> overall "improved" recording is to sound consistently improved.

----- if you read Thomas Stockham's "blind deconvolution" paper in the IEEE 
Proceedings (not to hand, so no precise reference, alas) you will be 
disappointed to find out where his logic breaks down. Essentially he says (my 
interpretation) "Caruso was a tenor, but only recorded acoustically. Jussi 
Bjoerling was a tenor, and he recorded electrically, so the linear distortion 
to the tenor voice via the acoustic recording process may be determined by 
measuring tenor tones on corresponding acoustic and electrical recordings. 
And since there was only one recording horn, you can then apply the inverse 
filtering to the acoustic sound." 

----- unfortunately this is a simplistic and flawed model for the recording 
process and postulating a similarity between Caruso and Bjoerling. As good 
tenors both had a peak in energy between ca. 2500 and 3300 Hz (the "singer's 
formant" -- Vennard simply calls it "the '2800' "), and it is usually one of 
the signs of a good operatic voice. Caruso did not apply this feature, except 
when he needed to, but Bjoerling's voice had a very strong "singer's 
formant", and in his case it was a steely quality that was always turned on. 
Now, if you simply apply a first order high pass filter to the SoundStream 
(Stockham) processed Caruso records, lifting the treble (removing the effect 
of his low pass noise filter), you suddenly hear Bjoerling's voice with 
Caruso's modulation. Strange to your ears. Stockham also worked on John 
McCormack's records, and in this case at least the voice belonged to the same 
person, so perhaps the chance of getting there was greater.

----- I have used some differing approaches, one of which was reconstruction 
of acoustic disc (not cylinder, like Fesler) recordings, using original 
Gramophone Company recording gear, some of which was now independent of EMI 
for historic reasons. Most of my results are not yet available publicly for 
confidentiality reasons (a world class tenor, and a record company that needs 
to be careful paid for the experiments). However, a couple of years later 
Sean Davies made acoustic recordings of a lesser tenor, and those were 
published at low intensity by EMI. The original pack of materials documenting 
that also had a video showing how the recording was performed - an 
artificially "aged" documentary.

----- I presented some of my results (even before the above experiments) at 
the 1986 ARSC Convention in New York. I know that after that, some of the 
sound restorers active at that time started to use similar approaches.

----- finally I should say that if you correct e.g. the Melba distance test 
recordings by inverse filtering the recording horn, diaphragm, and stylus 
bar, with headphones you have the most uncanny feeling of her receding and 
then approaching, even to use a reasonably low voice directly into your ear. 
The sheer depth of that simple recording is fascinating when it is correctly 
reproduced. I have no idea if the commercial CD versions permit this.

Kind regards,


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