I got curious about our Power Company 60 Hertz variations---& here's what I found----Verrrrry interesting From "Mike Holt's Forum"-----
:http://www.ornl.gov/sci/btc/apps/Res...NLTM200341.pdf was fascinating . It looks like +-0.01Hz is the normal operating range, with +-0.02 Hz intentionally used to adjust long term averages.
Evidence of long term (over the course of a month) errors on the order 0.004Hz is enough to get some people worried about the grid.
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.024 Hertz error divided by 60 hertz = .004 %----approx 1/2 of 1% fluctuation in 60Hertz voltage from power companies
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Turntable rurning at 34rpm is .666 rpm fast---divided by 33 1/3 (33.333) =.o199 %----Approx 2% fast
Lets say a 3 /12 minute recording----Thats 210 seconds times ..02 (2%) = 4.2 seconds
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I believe this would be just within factory "specs" for an "average turntable" with no speed adjustment---I think only a pro musician or a "Guru Audiophile" might be able to pick up on this----without an instant comparison for a "pitch" comparison. I have a couple of turntables with speed adjustment, & never do they read the same with a strobe & disc---sooo, It could be power line "Hertz"---or who knows what changes take place. I had nothing better to do tonight---I hope I didn't bore you---LOLOL !!!!!