@oberoniaomnia
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?
You are on the right track, but it gets more complicated! The reference tone as set out in measurement standards is 3150-Hz. The % wow and flutter is the maximum deviation from 3150-Hz on a weighted scale. The weighting is centred on 4-Hz and drops steeply on each side. 3150-Hz is chosen so it can be easily played on most devices!
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.
You are right again! Low frequencies or wow roughly correspond the with platter rotation speed, or the wobble of an off-centre record (2-Hz). Look at the frequency spectrum of what is played from the test record, and you will see 3150 smeared out, between say 3148 and 3152.
If only an off-centre record was to blame, the frequency would be spot on twice per revolution (2 x 2-Hz = 4-Hz, right where the weighting curve is highest), and way off in between.
Direct drive turntables tend to have low levels of wow because of the rotational mass and feedback controls of rotation speed, when compared with belt and rim drive.
Flutter is higher frequency, like say the motor speed of a belt drive or rim drive turntable. The frequency response will show extra frequencies further from 3150.
Direct drive tables tend to have worse flutter than belt drive, because direct drive uses impulses to rotate the platter while elastic belts tend to absorb vibration from higher speed motors.
Of course, the frequency spectrum will fluctuate over short time frames, so the standards say use at least 5 seconds. Measure the maximum difference over at least that time, after applying the weighting curve from the standards. So you will have a difference in frequencies which you can convert to a percentage of 3150-Hz.
Oh, if you actually want to read a standard, be prepared to pay around $50 to get a copy.
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!
I hope this has helped explain the measurement and why wow and flutter are combined these days. But so much for measurement, what can we actually hear?
Surprisingly, it depends on whether we are in an anechoic chamber or a reverberant environment.
Are you familiar with the concept of frequencies ’beating’? If two frequencies are close enough, you might hear a much lower frequency as the signals reinforce and then cancel. This interference phenomenon is a cheat’s way to get low notes for an organ.
In a real listening environment, we hear direct sounds and reflections. There is a chance that a sustained note from say a piano or a clarinet will interfere with reflections of itself. If the note is subject to flutter, when the reflected flutter is out-of-phase with the direct flutter, you may hear unnatural beats.
These are more likely to annoy classical audiophiles that those raised on jukeboxes full of pop music.
