Bottom line for me is that it is entirely possible to “hear” which of two turntables in an unfamiliar system does a better job with the rhythm in the music. Although more difficult and trickier it is possible, to a degree, to learn to recognize and extrapolate from how superior or inferior rhythmic accuracy might be affecting our perception of the tonal character that we hear.
I think Frogman is right.....
The ability of a turntable to maintain 'constant' and 'accurate' speed is able to be heard.....even if you're not a trained musician like Frogman 🤗
I have two turntables in my System (both with three tonearms).....one is a current model German-made belt-drive whilst the other is a 35 year-old vintage Japanese High-End Direct-Drive.
The belt-drive deck is nice, relaxed and tuneful......but does not possess the 'speed', 'grip' and knife-edge 'realism' of the direct-drive.
It's entirely possible though....that if you throw enough money, weight and technology into the construction of an uber-belt-drive deck.....it may approach the 'constancy' and 'accuracy' of the very best direct-drives.
As far as the question.... what are the 'limits' of our hearing ability to detect such minute speed variations?
I, like Frogman....don't know 🤪