"Pascal Schmidt" bravely wrote to "Roy J. Tellason" (18
Jun 05  13:52:42)
 --- on the heady topic of "cleaning old 78 vinyls ?"

 PS> My guess would be they use the laser, carefully positioned, to get a
 PS> surface scan of the depth of the record groove. Add a complex
 PS> mathematical model of how that surface would influence a regual pickup
 PS> unit and you can create a digital rendering of the original sound.
 PS> Most of the records I own are not too even, they have bumps and
 PS> sometimes even the middle hole is not really centered. I'd think it's
 PS> difficult to keep the laser positioned correctly.

I don't know the specific technique used but I think I could make
something that would work. If anything, I would have the laser
switching across the groove walls and not have it stationary. As the
laser scans the wall the reflected beam would return to an optical
pickup and the variation in intensity would be the actual audio
information. Stereo separation would be retrieved from a multiplexing
analog gate. Thus intensity information coming alterately from each
groove wall would provide the data for the audio. As for tracking, the
servo system would look for the deepest valley in the intensity as the
laser scanned the groove. OTOH individual optical pickups could be
used for each wall. There are other ways that come to mind.

 M*i*k*e

... TSR: Trashes System Randomly.
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