[ACHiPo]

There's been a bit of discussion about different turntable speed measurement techniques here and on other sites, so I thought I'd do a comparison.

I started with Turntabulator for my iPhone on the Apple Apps Store.  It uses the iPhone gyros and online reviews range from "fantastic" to "don't trust it--use a strobe disk".  Well I didn't have a strobe disk, but I have an iPhone, so I payed my $1.99, downloaded the app and gave it a spin (literally  ).  You don't need a record clamp with a flat top, but it helps (actually you do with a WTT because the iPhone is heavy enough to cause the platter to fall off it's 2-point bearing, but I did confirm that the readings were similar if the iPhone was on the platter instead of on the spindle by applying enough force to the spindle to keep it upright.  The other advantage by putting it on a clamp is that you can actually play a record while measuring--the stylus friction dropped RPM about 0.2 RPM).

Turntabulator Description

The app has two methods, quick and precise.  The quick method takes about 20 seconds, the precise method takes about 2 minutes.  There doesn't seem to be much difference in the accuracy between the two methods.

A little background:  I listened to a couple rock albums I hadn't heard in years and they sounded slow and a little lower pitched, so I was wondering if my Well Tempered Reference 'table was running slow, as there's no speed adjustment or feedback so I'd never checked it.

With the Turntabulator my WTT measured at 32.4 - 32.6 RPM --It was 32.6 RPM with a record clamped, but not playing.  It was 32.4 when playing a record, so the Turntabulator even in quick mode is precise enough to discern between a pretty small change in friction/RPM.  The Turntabulator gave me a "good" rating since the speed was within 3% (I slowed the platter with my finger to ~32 RPM and got an "okay" rating at ~5%).

I had a new belt that is about 2x the thickness which should increase the speed a bit, and sure enough the 'table measures 33.8 RPM with the new belt, within 1.5% and close enough to get an "excellent" rating on the Turntabulator.

All of this is well and good, but what if the Turntabulator is precise and not accurate?  I needed to compare a different method.  I still don't have a strobe disk, but I still have an iPhone, and several folks swear by Dr. Feickert Platterspeed, which calls for a 3150 Hz test tone.  Oops, although I've got a couple test records, I don't have one with a 3450 Hz tone.  Bummer.  But wait, further Googling turns up that the app now supports a 1 kHz tone, although it is more accurate at 3150 Hz.  Oh well, I'll take my chances.

Dr. Feickert Platter Speed Description

The measurement with the new belt using Platter Speed was 33.7 - 33.9 RPM, so right around the value I got with Turntabulator.  Platter Speed is a frequency measurement app, and provides raw and low-pass filtered performance data.  The mean frequency measured was 1018.8 Hz, or 1.9% high, almost identical to the Turntabulator results. 

Conclusions:  Either of these methods works, and will provide adequate accuracy and precision of turntable speed.  Oh, and the rock albums still sounded a bit slower and lower than I remembered, but I think they sound closer now

[dlaloum]

Now the difficult question - what about W&F?

[ACHiPo]

Now the difficult question - what about W&F?

Turntabulator does not do W&F.  Feickert will do wow and flutter measurements with a 3150 Hz tone, but since I wasn't considering changing turntables, and that's the primary way to change W&F, I figured ignorance is bliss.  Maybe once I get the acoustics of the room the way I like it I can obsess with upgrading my vinyl rig.

[Quiet Earth]

Now the difficult question - what about W&F?

External power supply for the motor.

[dlaloum]

There are various things that impact W&F - including arm damping...

but you cannot really work on it to improve it without a reliable consistent way of measuring it...

there have recently been discussions on both AK and VE about W&F measurement methods....

[Grbluen]

There are various things that impact W&F - including arm damping...

but you cannot really work on it to improve it without a reliable consistent way of measuring it...

there have recently been discussions on both AK and VE about W&F measurement methods....

Don't forget that the test records themselves probably aren't centered!

[catastrofe]

What a great idea.  If no objections, I'll try to expand on the testing this weekend as I have the following measurement tools available:

Kuzma Strobi
Platterspeed with 3150 test track
Android RPM Calculator App
Turntabulator for iPhone

I'll run them all and post the results.  The two tools I don't have are an old fashioned strobe disc or a Sutherland Timeline.

[ACHiPo]

What a great idea.  If no objections, I'll try to expand on the testing this weekend as I have the following measurement tools available:

Kuzma Strobi
Platterspeed with 3150 test track
Android RPM Calculator App
Turntabulator for iPhone

I'll run them all and post the results.  The two tools I don't have are an old fashioned strobe disc or a Sutherland Timeline.

Cat,
That would be great.  Thanks!
AC

[YoungDave]

I have used the Feickert speed measurement function that is built into the AdjustPlus setup system - it works well.  I also have a KAB Speedstrobe.  It works really well and can give you a readily apparent visual feel for the adjustments as you make them.

The drawback in both those tools is that they do not work when actually playing music.  If, as has been reported elsewhere (but which I have not personally verified), needle drag affects speed, these two tools are not going to help you identify that.

I have recently purchased, but not yet received, the new Phoenix Engineering Roadrunner tachometer http://www.phoenix-engr.com/#!/page_RoadRunner.  It will provide a continuous speed readout while playing music, to 5-digit precision (3 decimal places).  This device shows great promise as a measurement tool. 

For those turntables powered by synchronous motors, the Roadrunner also can be used to provide a feedback loop to the power supplies made by the same company, providing small frequent corrections in the AC power to the motor, to maintain a constant, correct speed.  I am less certain about its utility in this role, however.  It seems to me that a massive platter, massive flywheel, and powerful motors will possibly respond too slowly to corrective input, and result in overshoot and undershoot errors.  That is also the position of my turntable's designer, Harry Weisfeld.  He believes that a stable power supply and massive rotating parts will be superior to a feedback-corrected power supply.

I don't know - so for the immediate future I will be using only the Roadrunner tachometer to measure speed.  If I find that my turntable's speed varies with varying stylus drag, then I will consider adding the feedback-corrected power supply.

I will report back on the Roadrunner tachometer.

[neobop]

Stylus drag?
https://www.youtube.com/watch?v=RF2XieUlzvk

https://www.youtube.com/watch?v=RE52bsIh_ZA

neo

[catastrofe]

Okay, here is some "scientific" information.  All images are shots of Platterspeed results while playing track 10 of the Analogue Productions test record (3150 HZ tone).  My table is a Bergmann Magne air bearing/linear tracking.  Cartridge is a VDH Frog Gold at 1.47 grams VTF.

This first image is using the Kuzma Strobi as the record weight.  Without the track playing, the strobe drifted ever so slightly to the left.  Once I started playing the track, the strobe stabilized although I could still detect an extremely slight drift.  The shot below shows the Platterspeed results, which would contradict the drift I saw.



This next image adds my iPhone to the top of the Strobi to compare Turntabulator to Platterspeed.  With the test tone playing, Tuntabulator showed 33.37.  Without the stylus in the groove, Turntabulator showed 33.46.



Replacing the iPhone with my Motorola Droid Turbo allowed me to compare the Android app "RPM Calculator" with Turntabulator.  This app only goes to 1 decimal place, and showed 33.4 while the tone was playing.  Without the stylus in the groove it showed 33.5, which matches (with rounding) what Turntabulator showed.

[catastrofe]

Interestingly, placing my phones on top of the center weight did not seem to impact the speed of the table, possibly because the weight was centered over the bearing.

[NekoAudio]

I used Adjust+ and Platterspeed (iPhone 6) and got the same results. So I believe Platterspeed can be considered accurate.

[catastrofe]

I used Adjust+ and Platterspeed (iPhone 6) and got the same results. So I believe Platterspeed can be considered accurate.

Platterspeed is definitely accurate.  It seems that Turntabulator is also accurate.  RPM Calculator is too, but only displays one decimal.

[Halcro]

Stylus drag?
https://www.youtube.com/watch?v=RF2XieUlzvk

https://www.youtube.com/watch?v=RE52bsIh_ZA

neo

More stylus drag...?
http://youtu.be/R3Bf2ODgwdI

[WntrMute2]

There is a way of measuring stylus drag without additional fancy equipment.   I use my KAB strobe UNDER a clear record such as Lucinda Williams' West album.  Play the record and use the strobe to evaluate the changes.   Easy.

[neobop]

There us a way of measuring stylus drag without additional fancy equipment.   I use my KAB strobe UNDER a clear record such as Lucinda Williams' West album.  Play the record and use the strobe to evaluate the changes.   Easy.

You're not really measuring stylus drag, you're measuring its affect on your table as a percentage of speed deviation.  This might seem like technical nit picking, but stylus drag is friction not the end result.  The same can be said for the Sutherland blue light thing.  It displays deviation from absolute speed.

While absolute speed can define an overall characteristic of a table (PRAT), pitch is relative.  Musicians tune to a specific pitch whether it's absolutely correct or not.  If their pitch is the same, one to the other, then they're playing in tune.  What if they get on a gig and the piano is a little out of tune?  They have to tune to the piano.

Wow and flutter, instantaneous speed variations are more noticeable and its measurement is more complex.  You can't really compare manufacturer specs because they use different weighting systems and nobody checks their validity.  They can make up whatever numbers they choose, and they do.  Sometimes they don't even specify how the numbers are derived.

Both absolute speed and wow and flutter - speed deviations, are the Achilles' heel of record playing and one area where digital is superior.  If you want a great sounding record player, I think you should start with rock-steady speed and build from there.
neo   

[Wayner]

There is another element that has not been considered. Back in the old days of rock and roll, there were no computers do drive the music timing like there is today. Most digital music has the bulk of it generated thru MIDI and keeps the music pace constant. There also is no reel to reel to have speed variations to it, unlike the vinyl/analog format (multi-track to master to cutting the stamper).

On some older recordings, the table might be running perfectly, yet the listener might hear the bands pace change. It's not from the table, but from the band itself.

[WntrMute2]

You're not really measuring stylus drag, you're measuring its affect on your table as a percentage of speed deviation.  This might seem like technical nit picking, but stylus drag is friction not the end result.  The same can be said for the Sutherland blue light thing.  It displays deviation from absolute speed.

While absolute speed can define an overall characteristic of a table (PRAT), pitch is relative.  Musicians tune to a specific pitch whether it's absolutely correct or not.  If their pitch is the same, one to the other, then they're playing in tune.  What if they get on a gig and the piano is a little out of tune?  They have to tune to the piano.

Wow and flutter, instantaneous speed variations are more noticeable and its measurement is more complex.  You can't really compare manufacturer specs because they use different weighting systems and nobody checks their validity.  They can make up whatever numbers they choose, and they do.  Sometimes they don't even specify how the numbers are derived.

Both absolute speed and wow and flutter - speed deviations, are the Achilles' heel of record playing and one area where digital is superior.  If you want a great sounding record player, I think you should start with rock-steady speed and build from there.
neo

True enough but we are interested in the effect on speed from the drag of the stylus/groove interface are we not?  If the platter spins at one speed without the record playing and another with then compensation can be applied.   

[SurgeTO]

It seems to me that the Feikert 7" speed test takes into account the effect of the needle on the speed on the LP. So if you're concerned about that, then use this method to adjust the speed!