Direct Drive

@lewm 

I don't doubt that the average speed of a modern turntable is right on the money. But, according to accepted statistical theory, there is more to a phenomenon than just the mean.

Consider the platter speed to be a random variable whose distribution of values is some distribution D. Since a normal or Gaussian distribution is completely determined by two parameters, mean and standard deviation, if D ~ N(m,s) the situation is more complex than the mean. In general, the utility of mean as a unique determinant of a quantity is obvious when you consider wealth, like B Gates and one of us, etc. etc.

And a normal distribution is very well behaved at two parameters. Most distributions are described by more. These are the higher level moments, standard deviation (actually its square, the Variance; second), skewness (third), kurtosis (fourth), and the rest of the infinity of central moments have no common name. It is a theorem that any distribution can be uniquely described by its moments.

What this is all getting to, is that the higher order moments of the speed distribution are all noise, noise which is not much considered and not much measured. Our ears measure it though - it comes through as an almost sibilant brightness, a nasty sound. The best DD don't have much of this, but the big new Technics with its associated system seemed to produce way too much of that for me, when I heard a factory audition.

And what can we measure? Mean speed over a window of some duration.

To measure these higher order moments requires very many, very short window measures of mean speed, and applying the correct estimation algorithms. Shorter is better, and 14 bit resolution should be the absolute minimum. The fact that 'speed stability' is reported while standard deviation, skewness, and kurtosis is not, is revealing. It seems to be a matter of the engineering not keeping pace with either theory or perception, IMO.

What do you think?

@pedroeb  Make that the Premotec 9904 111 31813 (as it was then designated), then available from Element 14, IIRC.

Terry, amidst all the verbiage and math, are you saying you heard an SP10R and it was noisy even compared to older Technics DD turntables? Or what are you saying?

By the way, JP Jones analysis took into account and measured speed changes over very short time intervals.

I've owned AR, Thorens, Lenco, Gerrard, Philips, Dual and ProJect Debut Carbon turntables, most of them manual (that old classic AR is just a platter, tonearm and on-off switch). The ProJect was the last to be replaced—by a Denon DP-37F (so, a lower-end Denon direct drive). The Denon, with an Ortofon 2M Blue cartridge, blows all the others away in every relevant category: speed constancy, lack of wow or flutter, lack of rumble, transparency of sound...and, of course, convenience of use. It performs its various automatic functions like a ballet dancer, and the very easy to use cue button is extremely precise in where it picks the arm up and puts it down. The only reservations I have about this table are theoretical. The arm's parameters are mostly controlled by a chip; when you turn the power off, the arm floats. So, both tracking force and anti-skate are somehow provided by computer. But I've owned the table for three years now, and had no problems at all with it. And the tracking force settings are accurate, as confirmed by a scale. So are the anti-skate settings. The whole rig (minus the 2M Blue, which I bought new) cost me about $200. It sounds as good as Red Book CDs (I've got several recordings on vinyl and CD of the same thing—e.g., the famous Kleiber performances of Beethoven's Fifth and Seventh), but SACDs (again, of the same recordings) sound marginally better.

ProJect Debut Carbon Total entry level TT.

My Thorens TD145 is fantastic. Built in the 1975 and I had it professional restored with a custom plinth. Rewired the TP-16 tone arm with Cardas Clear Phono. Has MP110 MM Cart (love it).

@dover , you always make this claim about DD tables. Please provide your documentation to back up these claims. You do know that "jitter" is something that happens at a fairly high rate. I'm sure a steady test tone would reveal this pretty easy, and be easy to document with numbers. Rather funny that I haven't seen these reports.

BillWojo