Is anyone working on a reasonably priced turntable to play vinyl discs without degrading them? In the mid '80s, Finial Technology announced such a turntable, and had a working unit at CES in 1986. It had a stylus that contained laser interferometers that could very accurately and precisely measure the distance from the stylus to the grove walls. It kept the stylus near, but not touching, the groove, getting the audio…
My very limited understanding after talking to someone who was interested in this stuff, is that people are concerned with quantizing of the signal, which will happen with that laser solution. I’ve heard this is why audiophiles also use magnetic tape. To be clear I heard this second hand and am not directly familiar.
I don't think the correspondence would be linear. There's probably something like cos(2 pi d / W) in there somewhere, where d is the distance to the grove and W is the wavelength of the laser. So you'd need some sort of equalization circuit on the output, but audiophiles are OK with that--they are used to RIAA equilization on vinyl already.
I assume that the variations in groove distance are much larger than the wavelength of the laser, which would mean that there are several plausible grove distances that give the same intensity output of the interferometer. I'm not quite sure how to handle that. I have a feeling an integrator would be involved, but details elude me at the moment.