Measuring turntable speed


Happy Holidays everyone!  This has probably been discussed before but I'm of the age that makes me a bit of a Luddite.  I have a VPI Scout and SDS.  I use "The Ultimate Analogue Test LP" to play the test tone and (at least I used to) the app Dr. Fridrekson(??) had other there.  It mysteriously disappeared from my iPad and I can't find it anywhere.  What are you using?  Thanks!
scarlson
Fun gear!

So you put one reflective strip on the edge of the platter. And you lay the device down so you don't hold it (movement of holding it introduces in its own fluctuations).

But if we stop and think about it a second.

Manufacturer of TT measure and specify speed as wow and flutter.
This measurement quantifies the amount of 'frequency wobble' (caused by speed fluctuations)
Source:
https://en.m.wikipedia.org/wiki/Wow_and_flutter_measurement

So let's look at the "speed fluctuations" that a DT-2234+ digital tachometer can capture:
At 33⅓ rpm the platter has done little more than a half rotation. And you need to wait almost another half turn before you get the next measurement. With out taking into account the variance of the tachometer itself  ± 0.1 rpm.
(33⅓ rpm / 60s = 0.5555 RPS) 
So almost 2 seconds between each measuring point.

During the elapsed 2 seconds the "speed fluctuations" can easily have been momentarily fluctuate between +0.25% AND -0.25%. But that fluctuation is something you don't pick up and totally miss during the ~2s wait.. we only get a average over those ~2s.

Here is a example of how rapidly the speed is fluctuate during 2s if we use a better method with a greater resolution:
https://imgur.com/a/Vmz7CrU

Measurement is usually made on a 3.15 kHz (or sometimes 3 kHz) tone, a frequency chosen because it is high enough to give good resolution, but low enough not to be affected by drop-outs and high-frequency losses. Ideally, flutter should be measured using a pre-recorded tone free from flutter.
Source:
https://en.m.wikipedia.org/wiki/Wow_and_flutter_measurement

As seen in the Imgur link above in this post we here measure EACH 0.1s something that have 3150 samples each second.. It a whole lot another resolution that a stroboscope never ever can give you.

Yes, why is this useful? Is it not lunatic? 
This resolution enable you to see if you get less fluctuation if you add a standard 500g clamp (center/ring)... Will a 500g addition that add the rotating mass (inheritance) to make your platter to fluctuate less?

With a strobe you will NEVER know..

You can also catch if your speed is drifting or is rock stable the same after a week or so. Small shanges is impossible to capture otherwise. Like when changing belt or maintenance with oil change and so on..

All you need is a calibration disc/LP (that you can calibrate other things also with). And a vinyl lover have to have one of those anyway!
And a old discarded android phone $0 (or your present one) and just download the app. 
(See my previous posts)

You can save and load measurements and compare them. Of course you can adjust the speed on the 45rpm also.

So why pay money for a stroboscope when you can buy a test record instead that with the other tracks you can measure other things.. the strobe can only measure one thing and that is done rather poorly relatively compared to the standard way of doing it... I don't believe that I am smarter than the girls and boys behind standardisation institutions like specifications (that use a variant of this procedure):
  • IEC 386
  • DIN45507
  • BS4847
  • CCIR 409-3
  • AES6-2008
But who don't like new toys? :)
Is your graph more accurate  than a wow and flutter meter???  Been playing with a test record and wow and flutter app lately.

Thanks 
Tom
I've been using the same one big greg mentioned. (Also paid full price for it :-)). Run the table with VPI's ADS. I check speed a couple times a year. It doesn't change.
Optimize, I know of no turntable were you can adjust wow and flutter. I know a bunch were you can adjust the speed. Thus a device measuring 3150 times a second is no more useful in adjusting speed than one measuring every revolution. It is revolutions per minute after all.

Is your graph more accurate than a wow and flutter meter??? Been playing with a test record and wow and flutter app lately.

Thanks
Tom

Do you mean a meter like this?
https://youtu.be/0G2kU1e9Cpo

I think that we may not need more accuracy or what to do with more accuracy than that.
That is not the game. You need enough accuracy  and resolution to be able to make different decisions lit the examples above.

When you have enough accuracy and resolution to measure the fluctuation constantly the same between measurements. By using the same method and equipment.

In the app that I used, it is written:
"You can now calculate wow of your turntable in accordance to DIN IEC 386 (formerly DIN 45507) using the recorded chart data! Expensive special equipment was needed before to do so!"

That tells me that the app developer thinks that he has and use the same method and resolution to calculate the results. As complies with the mentioned DIN standardisation.

I believe this is "good enough". With the saved graphs and with the calculations as seen in the lower left corner IS better than only a analogue meter showing only a temporary value/level and not the other mentioned calculations.
Best regards.