A sticky patch on the platter, giving the belt a "twang" every revolution could excite the turntable resonance, looking like this
I did a bit of looking into it, the Analogue productions test lp was cut on a Neumann VMS 80 at sterling sound.
On here:http://sterling-sound.com/mastering/vinyl/#3
And I quote "The VMS 80 computer divides each rotation of the platter into sixteen increments"
16 increments works out to be 8.88hz, visible on most the spectrums, particularly the Yamahas. It also showed up on my DIY turntable plot.
Damn , you beat me to it !I used to have one of those when I was a kid. Great fun, it was.
With a bit of practice you can make nice patterns, like Paul's.
Joe
I assume that these days no developer needs one of the old meters when a suitable ADC and computer can do as good a measurement or better via software.