How to set SRA after determining true vertical?

Greg, maybe you (or Doug or I) can find some microscopic groove photos that will show this rake or slant in the groove undulations clearly. I know Last used to show such photos with their products. I'll see what I can find.

Neil

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Nsgarch- I found a picture of the groove. Results are inconclusive.
Doug-Just off the top of my head I might get similar results with a router.
I guess the burden of proof is on me.http://aolsearch.aol.com/aol/search?query=pictures+of+record+groove&invocationType=spelling&itaq=0.2.1.KQzKRxLUFAB&itaq=1.0.1.pictures+of+record+groove&itaq=2.1.1.I hope that takes you to a picture of record groove and compact disc digits. If not just type " pictures of a record groove" on your aol browser. Taken by elctron microscope.

Greg - good pictures! I think the high-mag one shows pretty conclusively that the groove undulations slant -- in this case toward the bottom of the picture (from bottom to top of the groove.)

Great pix!

If we imagine a line contact stylus trying to trace those modulations, if SRA is off then one end of the contact line will encounter each modulation before the other end. The stylus will shave across the modulation instead of tracing it precisely.

Mechanically (sonically) this will:
1) reduce stylus deflections (reduced micro-dynamics),
2) lengthen the time the contact line sees each modulation (temporal bloat),
3) alter the timing of when the stylus encounters multiple frequencies (loss of temporal focus and timbre) and,
4) alter the frequencies the stylus actually plays (FM distortion).

I hear #s 2 and 3 most easily. Paul is very sensitive to #1. He was able to adjust SRA on Cello's rig just by feeling the pressure waves coming off the woofers, without actually listening at all. Raul says he adjusts by listening to bass, so his sensitivity may be similar to Paul's.

P.S. Those records could use a good cleaning!

http://www.smartdev.com/LT/Align.htm. more drawings.