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Peter Copeland wrote:

>     I agree, and must add another dimension to solving this problem - my
> twopennyworth! The only practical way to do a three-dimensional map of a
> groove (whether hill-and-dale, lateral, or stereo) is to use a test probe
> controlled by a digital device of some sort. However, there is no
> anti-aliassing filter for the data. Therefore the wanted sound is going to
> be corrupted by an enormous amount of aliassing, and ultrasonic components
> will become "folded down" into the audio spectrum.
>     The fundamental idea is a good one, but I'm afraid I cannot see how to
> get around this problem - *except* by playing the groove with a stylus and
> having an anti-aliassing filter *before* the result(s) are digitised. If
> anyone can think of how to conquer that, it *would* be a good idea!

I agree with you that if the fineness of the 3-d topographic data is
insufficient (it is too course), then it will not accurately enough
represent the contours of the groove walls. That's why I commented
that the amount of data needed to be gathered for a single disk is
very large (I did a back of the envelope calculation and came up
with well over a gig of 3-d sample points -- a lot of data, but by
today's standards is not that onerous.)

The idea is to sample enough points that it would even be possible, if
one has precise enough stereo lithography equipment, to create a new
disk from the data and be able to play it traditionally!

Now, to gather the data, it would probably be some sort of
triangulated laser system which can precisely measure the height of
any spot on a record. As I noted before, it would not surprise me if
such equipment already exists (for precise contouring of rough
surfaces for research purposes). If it doesn't exist, I'm pretty sure
it could be built.

If anyone here in a university or archive research organization is
interested in pursuing the conceptual research into this idea, I'd be
willing to assist -- I do have credentials having worked as a staff
scientist at Lawrence Berkeley Laboratory and mechanical engineer at
Lawrence Livermore Laboratory, with a solar energy stint at Sandia
Labs.

Jon Noring