@yogiboy Thanks for the 4 Hz cut off value. But what does that mean in reality? 4 Hz = oscillation 4 times per second, but of what? A reference tone, say a' = 440 Hz. But then what does 0.1% of >4 Hz mean?
I would have expected some variation of the platter rotation (33.33/45 RPM) to be the metric of wow and flutter. but then we need a time dimension (seconds) to differentiate short from long term variability. Or does 4 Hz refer cryptically to 0.25 s? For easy math at 30 rpm, one revolution takes 2 s, so 0.25 s would be 1/8 of a revolution or 45 degrees. but then > < is not a terribly good engineering standard.
The more I try to figure out what that 4 Hz could mean, the more I get confused. Either there is more to it, or it does not make any sense. If you (or anybody else) can provide some clarity, that would be great! Thanks!