Dear Jean: *** " Whether its called PRaT, or whatever, arent we all looking for the visceral, emotion-filled, faithful reproduction of the stuff in those grooves? " ***
I agree totally with 4yanx.
*** " this is the best way to evaluate the performance of a turntable combination rather than introducing various flavors inherent in tonearms and cartridges and comparing those. " ***
I agree too with Lugnut.
*** " mean truly accurate speed, in practice and playing a real LP) being seminal in this regard. If these Big Heavyweight turntables fail to recover PRaT (as any do, I had the Maplenoll Ariadne with 40-pound platter which was less musical than the Athena with the lighter 15-pound platter it replaced), it is because their speed stability is in fact not stable " ****
Jean this is not true : The PRaT or not PRaT of any turntable depends of many factors: speed stability, rumble, bearing type ( air bearing, magnetic bearing, oil bearing, non oil bearing, etc ), platter material ( wood, acrilyc, metal ), heavy mass type or other type, belt or thread drive ( thread are the best for heavy mass metal platters. Not very good with wood/acrilyc ones . ) suspended or not suspended, in which kind of plataform is mounted, which tonearm, which cartridge, which phono cables, which phono preamp, which speakers, which amplifiers, which recordings, etc...
As you can see it is a very complex subject and the speed stability is only one of the parameters, yes is a very important ( critical ) one but as I told: is only one.
The must important issue on what Jean already told us is that we have to remember that the turntable " exist " first because we have to retrivial the recording information through it ( the only way ) and second that for do that in an accurate way ( accurate to the recording ) it has to run exactly at 33 1/3 or 45 rpm. Any deviation it will be audible an out of place: it will be inaccurate and if does not exist that speed stability we will hearing a different recording ( due to timing. Jean you are right in this issue ). That speed stability has to be in the long and short run.
Which will be the criteria range for that speed stability?, well at least the turntable has to have a speed accuracy of: +,- 0.01%. Less of this " figure " is not permisible for a high-end turntable. The best ones, like: Walker, top Basis, top VPI, Verdier, Acoustic Signature, Well Tempered, Top Sota, Nothingham, Micro Seiki, Maplenol, meets and surpass this speed criteria ( example: Walker: 0.002% ). All these units are belt/thread drive systems. The direct drive systems easily meets that speed criteria: Technics SP 10 MK 2/3, Denon DP 80/100,: 0.001% ( The Sirius that is a direct drive TT obviuosly is at the top of the target ).
Now, this speed stability depends on many issues: bearing type, platter balance, platter weight type, motor quality, etc..., but all things the same, the difference will be on the: power supply. Take a look on the power supply ( some are stand alone units, like Walker and Acoustic Signature TTs. ) and you can see how elaborate are the circuits and then you can understand why it is so important and critical for speed accuracy the power supply design.
Now, all of you: your turntable meet, at least, the 0.01% speed accuracy criteria ?. If not, you are in problems, I really mean: the music reproduction is in serious problems.
Regards and enjoy the music.
Raul.