Turntable speed accuracy

I agree with Dertonarm on this subject. DD turntables vary due to their designs and construction. Some are very accurate. String drives can indeed be very accurate, as long as the string is fresh. Idler drives, the one I know a little about, have an inherent tracking error of around one part per million, depending on the footprint of the idler wheel itself. Belt drives are not so inherently accurate as the others, although advances have been made to alleviate belt creep through various workarounds and, of course, the recent use of tape.

So, a controller should be pretty accurate, but exactly how much? I believe one part per million accuracy is reasonable, but if we do that, we can easily substitute a standard clock with an OCXO (oven controlled quartz oscillator) with GPS referencing, which can improve the accuracy of a properly designed controller to around one part per trillion, or better. Can anyone hear the difference with such a controller connected to a turntable that is only capable of one part per million accuracy due to mechanical constraints? Certainly, the math doesn't warrant the extra effort, but at least all bases are covered. Would such an accurate controller be warranted with a proper string driven table? I don't know, but virtually anyone can hear a measurable difference with a good controller. That much I do know. If you have the opportunity to compare a turntable without a controller to the same setup, but with a good controller attached, listen for little parts of music that we never typically use as a guide, like small sounds from background reed instruments. You might be surprised.

Win

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Most turntable owners believe, they get a Product which is done right, more or less perfect for the money and all they have to do as next step to think about the ultimate technical solution (independent from price).
This is another common wrong way in audiophile existence. When we go back to the basics, lets think about the belt. Most of them are so horrible from quality and specs, it is hard to believe. Basis did a better work but most belts I tried produced so much drift, that any discussion about following Design features were wasted time.
Even with a heavy platter like shown in the picture showed me results, which were amazing ( really depressing what some 'manufacturers' offer us as 'High End'.

Belt comparisons..

These comparisons are even more depressing with light Platters....
The Audiophile gets what he deserves. Marketing and Fangroups can replace a lot today ....anyway...fun counts.
Tomorrow is another day to transform a big orchestra in a lifelike presentation into a owners home who did a lot of things right....

Nice horns. Seems a real shame to produce all of that analog music and then run it through digital time domain processing. Sorry, the purist in me won't shutup. :-)

How can correct turntable speed as well as excellent speed stability possibly NOT matter and be of the utmost importance? Rhythm and time is where the heart and soul of music lies. Any technical considerations that may have an effect on these are of the utmost importance. I am constantly perplexed by how often audiophiles agonize about minute changes in areas that affect the tonal/timbral characteristics of their audio systems, but are willing to forgive much larger deviations from truth in the area of time and rhythm. 

I hope we can agree that our audio systems exist to be at the service of the music. Musicians, not audio systems, make music; and musicians  give a great  deal of importance to performance considerations that relate to the perceived effects of correct playback speed and speed stability. The changes in pitch as they relate to performance standards are more subtle than what is generally discussed in relation to technical accuracy in turntable systems. These considerations are not arbitrary, but relate to the emotional impact that tuning has on the music. This is not only the players' consideration, but sometimes also the composer's intent. It is well 
documented that many composers chose to compose in a particular key because of the emotional effect of one key versus another. Likewise, orchestras or individual players will often tune their instruments to achieve a particular sound and it's resulting emotional effect. If we are going to worry about the effects things like slightly raising or lowering VTA, why dismiss the effect of these other considerations when these relate much more to the core of the music? 

Speed stability is even more important as it relates to these considerations. Excellent comments have been made above about the importance of these. There is no question that extremely subtle deviations from absolute pitch stability are quite audible. As has been pointed out, even the very best belt drive tables suffer from these distortions. What is really insidious is the effect that these distortions have on the emotional impact of the music, and the ability of the music to engage the listener. As this relates to musicians' performance standards, I would like to point out that the effects from the absence of absolutely stable playback speed on the music is not nearly as subtle as the considerations that musicians give to absolutely stable and accurate time and rhythm during a performance; these can be the effect of anything from simply the mediocre sense of rhythm on the part of a particular musician, to wether a musician had too much coffee that morning (I kid not). If we can agree that these things matter during a performance, how can similar effects not matter a great deal during playback?

Peter,

Sorry for the hyperbole.

Our own TT's speed stability did go through two periods where it drove us nuts. We heard the first problem yet no commercial strobe showed it. Paul built a custom, higher resolution strobe and we captured many hours of data to demonstrate the problem to Teres. The data helped Teres identify a problem in their motors but it took them three months of testing and measurement to confirm that the redesign/rebuild actually fixed the problem. The other problem was subtler and was addressed by our own experimentation with better belt materials and implementations.

That Aries was a touch soft on transients but much better than most BD's we've heard. In our experience many (mostly less costly) BD's are unlistenably bad due mostly to poor belt materials, as others have said.

OTOH, concluding that idler wheel/rim drive designs are inherently better than BD's would be going too far. We've had such a design in our system, made by Teres, and it was audibly inferior to our carefully worked out BD. Implementation is always critical and individual cases may trump general rules.