FD400 drive troubleshooting

I think he's probably wrong. Most people probably can't, at least not without a side-to-side comparison (I could sure hear the beat frequency if listening to 450Hz and 451.1Hz together, but feel sure I could not tell the difference in isolation, likely not even in a non-simultaneous A/B listen). But some of people with better "perfect pitch" (which actually isn't perfect, just substantially more precise than most people's pitch sense) could, I expect, tell you which is which even in isolation. One other thing is that mains frequency may not always be a good 50/60 Hz reference (which will, of course, affect things like the floppy speed calibration that started this thread off, if it's using the power mains as the frequency reference). The power utilities go to some lengths to make sure it averages out to that over periods measured in days, because of all the clocks that depend on it. But in the short term - seconds and minutes - I've read that it can vary slightly (the figure I recall is 1Hz or so) for various reasons, at least one of which is deliberate compensation for the others. :) I'm not sure how plausible this actually is. Given how mains power distribution works, it seems to me that the entire grid must perforce be running at the same frequency, or parts of it will drift in and out of phase with other parts, causing problems at the various points where one utility sells power to another. This means that tweaking the frequency would require grid-wide collaboration, difficult even for grids as small as England's, that much more so for grids like the North American one. Or do they use monster M-G sets or the like to deal with that? :-) /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse at rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B