Re: [ARSCLIST] Dynamic-frequency Range

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 21/10/06, George Brock-Nannestad wrote:

> ----- 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."

This is completely different from what I was suggesting. You need an
impulse signal such as the sharp click from a spark to derive a function
for deconvolution.

Simply comparing one tenor with another and adjusting some EQ is not at
all the same.

+++++

Imagine an image which has been spoiled by camera movement during the
exposure (or in the case of an astronomical image, by air movement).
There will be a certain smudge which is applied equally to each pixel of
the image. The image is said to be convolved with this "smudge"
function.

In reality there will be a complex function involving optical
aberrations, light spread in the sensor, and movement.

Provided there is some point source in the image, such as a star, which
we know should be represented by one pixel, then the function can be
measured from the actual multi-pixel image of the star. It is then
mathematically possible to deconvolve the image and remove the
aberrations and smudging (in practice, to some extent).

The nearest audio equivalent to a star is an impulse signal such as the
sharp click generated by a spark at high voltage. 

The big problem is that noise makes it hard to derive an accurate
convolution function. However, averaging from a number of clicks would
help.

 
> ----- 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.

I'm not sure what you mean by "filtering" but I suspect it is some kind
of frequency-dependent approach. Deconvolution is not a form of EQ.

The Melba distance tests do give a strong effect of her receding on the
Ward Marston Naxos transfers, on my equipment.

Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx

Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx