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Susan Stinson wrote:
> Hello, Tom:
> Actually, no, they don't.  As we are experiencing in the development of
> our cylinder laser playback system, the laser beam picks up whatever the
> groove modulation has to offer, including particles of dust, wax, and
> malformations caused by mould activity.  It seems, reasonably, that once
> the mould has arrived and done its _thing_, there is no fix.

With the advantage of perfect ignorance, I suggest that you may be too 
pessimistic. The day may come when sophistication in the use of the 
laser will pay off. On the simplest level, scanning with two lasers at 
different frequencies will allow differentiation in a remote-sensing 
effect: the mold will have different transmission and reflectance 
properties in the two (or more) colors and that may be exploited. More 
sophisticated techniques, even tomography, may become possible in which 
the mold would become transparent to the pickup. Certainly, the cost 
would be high, but it might not remain so and it may be worthwhile.

Some years ago, a friend was hoping to recover audio quality from an 
optical track on old film. (He was with Warner at the time, is now with 
Microsoft.) We investigated and had some success with gray-scale pickup 
and algorithms for inferring the shape of the waveform and correction to 
the two (symmetric) profiles - one on each side - which gave the 
highest-probability reconstruction of the original. Our tools were 
simplistic and the results were preliminary, but they certainly went far 
beyond the de-facto thresholding of conventional sensors.

Mike
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