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In Reply to: RE: The groove helix is a mirror-image of normal. posted by Kal Rubinson on November 26, 2013 at 06:43:28
I don't quite understand the mirror image idea. I tried it it on a piece of paper and looked at it in a mirror. It doesn't seem to work unless the turntable turns in the opposite direction, but the music still starts at the outer edge. Am I missing something?
I have about six of those Fortissimo records. I picked them up cheap at record swap meets. The groove is cut from the inside to the outside and simply guides the stylus from the inside to the outside. The lathe needs to be modified so the cutting head moves from the inside to the outside, rather than the opposite as in normal disc cutting.
It's awkward to drop the stylus in the inner groove if you don't have the drop/lift lever on your turntable.
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In mirror image writing like da Vinci did, the image only changes from left to right, it doesn't change from top to bottom.
Try holding a normal record up to a mirror. The music still starts at the outer edge, doesn't it? A turntable turning in the opposite direction would play it normally.
I don't see that drawing a mirror image is any different from seeing it in the mirror. Maybe I've had too much turkey. Oops, I'm in California, and Thanksgiving dinner is still many hours away :-).
AI don't understand all the confusion. A standard record starts from the outside ans spirals inward. This other type starts at the inside and spirals outward. What's not to get?
The reason that I suggested making a mirror image drawing rather than looking at it in the mirror is that the former will let you turn it as if it was on your turntable and you can (should) see that putting the stylus at the label will cause it to track from inside out.
But the music will play backwards. It will be like a 2-track stereo tape wound tails out and played without rewinding first.
Write down the alphabet on a paper thus: abc....xyz and put an arrow in the direction the information reads.
Draw a spiral on the same paper (1½ spiral is enough) with an arrow to show the direction the information reads.
Look at it in the mirror. You will see that the information will only read correctly on the spiral if the rotation is reversed. The mirror image doesn't make the music start on the inside, so for me it's an imperfect comparison.
But I give up.
.
The mirror bit was just to show you how the stylus would track the groove from inside to outside with the turntable running in the standard direction.
It was always presumed that the recording would be cut in the same direction that it is played, otherwise the music would be backward.
This whole mirror image thing has complicated the matter .The direction of the cutting remains the same. In one case the grooves move from outside to inside and the other case the grooves move from inside to outside. Simple
Alan
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