Turntable speed accuracy

In absolute terms there is no such thing as perfect speed stability. There is always a finite amount of instability. It's like saying a surface is smooth. A smooth surface looks like a mountain range under a microscope.

So the right question is what level of speed instability is audible? It is a fact that uneven drag from a stylus will affect platter speed. But is it enough to be audible?

To the novice it would seem that a good motor and a heavy platter will push instability into the in-audible range. Early work with digital encoding fell into the same trap. Who would have imagined that infinitesimally small timing errors in the tens of pico seconds would be audible. Well, it is clearly documented fact that these microscopic errors are audible. This tells us that our ears are far more sensitive to errors in the time domain than anyone would have imagined.

In my opinion achieving speed stability such that there are no audible artifacts is something that state of the art turntables approach but never quite meet. My experience has shown that there is always room for improvement when it comes to speed stability.

All I know is that the wavering on the decaying note of a piano is REALLY annoying and that usually happens on belt-drive suspended turntables with stretchy belt. I may not know what I like but I know what I don't like.

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AC line frequency in the US is adjusted within .02% and accurate within .033%, the KAB strobe is accurate within .03%.

AC from the power line is as accurate. The KAB website info is WRONG! A light bulb and strobe disk is as accurate. END OF STORY!!!

From Wikipedia

Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 and the invention of the electric clock driven by a synchronous motor. Network operators will regulate the daily average frequency so that clocks stay within a few seconds of correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at the nominal value within a few hundred parts per million.[19] In the synchronous grid of Continental Europe, the deviation between network phase time and UTC (based on International Atomic Time) is calculated at 08:00 each day in a control center in Switzerland, and the target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 24×3600×50 cycles per day is maintained.[20] In North America, whenever the error exceeds 10 seconds for the east, 3 seconds for Texas, or 2 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half hour.[21][22]

My last post should end this thread.

The VPI SDS adjustment, a strobe and light bulb, or a $100 KAB strobe, "are all" about as accurate as your AC line frequency!

How do all you "SUCKERS" feel, that payed $100 for the KAB BS!

When I am playing Vladimir Horowitz on my turntable should I ask him to stop on the half hour Eastern Standard Time so I dont have to listen to the speed corrections ?

Seriously though when I was selling Elite Rock Townsend turntables which used an AC motor, when I corrected the operating voltages from 69.9 to 70 volts, even though AC motors are supposedly dependent of frequency not voltage, the sonic presentation changed from that of a Van den Hul to a Koetsu without changing the cartridge. Something was going on - motor resonance, optimum torque, minute speed changes - who knows.

Atmosphere is right there are many things we hear that are not measurable.

A sinewave doesn't tell you whether the pianist was happy or sad when they hit the note.

By the way the 0.02 is the correction of the AVERAGE fequency deviation - that is quite different from the real deviations in frequency.