• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Different Results from Speed Measurement Apps

OldSch00l

OldSch00l

Seeking a Happy Medium
So I got myself a new Atma-Sphere belt for my Empire based on numerous recommendations from other AK members, and with the thought that my speed was off. What I ran into in the process of trying to set the speed correctly was that the 2 different apps I used to measure it gave me significantly different readings.

The app that I had been using for some time was PlatterSpeed. I have a test record with a 1Khz test tone that I would play, and PlatterSpeed would recognize that I was playing a 1K tone and tell me what the _actual_ frequency coming out of the stereo was - and I would then adjust the speed from there until it read 1K.

A week ago or so I came across another app called RPM Calculator. This is one of the apps where you actually set the phone down on the platter and it displays what speed it is rotating at. How accurate this reading is I am not sure.

After setting the speed of the table using PlatterSpeed and a 1K tone so that it is reading 33.3rpm, when I put my phone on the platter and use the other app - RPM Calculator - it tells me that the table is running fast (~34 rpm).

The question is, which should I trust? Does anyone else have experience with using either or both of these apps? My gut tells me that the method PlatterSpeed uses should be more accurate, as I am not sure how accurate the accelerometer in the phone is...
 
Register to hide this ad
Dinosaur here- I always use a strobe disc and a neon light. Various other light sources will work, as long as they modulate with line frequency. Some people doubt their line frequency, but it's invariably almost dead on.

Most people have access to accurate clocks with a second hand. Put something on the platter and time 50 or so revolutions, then calculate the speed. That will be one of the most accurate ways- the more revolutions, the better it is.

My arc template generator will also print very nice large strobe disks, with a mark and instructions for timing- http://www.conradhoffman.com/TemplateGen.zip
 
Last edited:
No experience with either as I am a dinosaur too but I would trust the tone more than the unsecured object rotating on a platform. Perhaps the phone has just a bit of wobble?
 
The tone seems more high tech, but there are too many places where it can go wrong. The signal generator needed to be dead on frequency when they recorded it, and the cutting lathe needed to be dead on speed. Finally, whatever you're checking it with needs a good reference frequency and the software has to be bug free. All those things aren't that difficult, but too many steps are involved that you have no way to verify.

When you measure with a strobe disc or by timing, you're comparing the actual thing you want to measure, with a single reference time/frequency source.

Another thing to consider is wow. With a strobe disc it's easy to see brief variations, without losing sight of the overall drift. With a strobe disc off-center, you'll see wow from the error, but with it perfectly centered you can see what the table itself is doing.

With the timing method, you have the advantage of a very long test period and can get almost unlimited accuracy for the long term speed. Consider that any cheap quartz watch might be within a few seconds a week, which is a few parts in 604800, so the only practical limitation is how many revolutions you're willing to time to get an accurate number of seconds. It's actually the method I'd use as a reality check on any other method because there's so little room for error.
 
Last edited:
Yeah, I'm starting to think I should get either a strobe or possibly try the timing method....

For what it's worth, my phone is firmly positioned on the platter when I am using the RPM Calculator app. I suspect that each phone model's reliability is different regarding it's technical ability to accurately determine it's rotational speed using it's internal sensor suite. Which also leads me to question the accuracy and response of the microphone being used to measure the audible frequency with the PlatterSpeed app....
 
My experience is that the rpm calc app is +/-0.2, I've yet to try the 1k tone because all I have are the audio obstacle records and I've been too lazy to check to see if they have it.
It just seems that NONE of the Quartz lock tables have read 33.3 with rpm calculator, seems suspicious.

IMO

Ben


Sent from my iPhone using Tapatalk
 
Four hundred simoleons?!?!?! I'll stick with a strobe disc and a hockey puck. ;)

Strobe discs are fine. While there may be slight variations in mains current from place to place or time to time, the frequency, 50 Hz or 60 Hz, is really very consistent and the frequency is what the strobe discs depend on.

John
 
OldSch00l said:
So I got myself a new Atma-Sphere belt for my Empire based on numerous recommendations from other AK members, and with the thought that my speed was off. What I ran into in the process of trying to set the speed correctly was that the 2 different apps I used to measure it gave me significantly different readings.

The app that I had been using for some time was PlatterSpeed. I have a test record with a 1Khz test tone that I would play, and PlatterSpeed would recognize that I was playing a 1K tone and tell me what the _actual_ frequency coming out of the stereo was - and I would then adjust the speed from there until it read 1K.

A week ago or so I came across another app called RPM Calculator. This is one of the apps where you actually set the phone down on the platter and it displays what speed it is rotating at. How accurate this reading is I am not sure.

After setting the speed of the table using PlatterSpeed and a 1K tone so that it is reading 33.3rpm, when I put my phone on the platter and use the other app - RPM Calculator - it tells me that the table is running fast (~34 rpm).

The question is, which should I trust? Does anyone else have experience with using either or both of these apps? My gut tells me that the method PlatterSpeed uses should be more accurate, as I am not sure how accurate the accelerometer in the phone is...
Click to expand...

ConradH said:
Dinosaur here- I always use a strobe disc and a neon light. Various other light sources will work, as long as they modulate with line frequency. Some people doubt their line frequency, but it's invariably almost dead on.

Most people have access to accurate clocks with a second hand. Put something on the platter and time 50 or so revolutions, then calculate the speed. That will be one of the most accurate ways- the more revolutions, the better it is.

My arc template generator will also print very nice large strobe disks, with a mark and instructions for timing- http://www.conradhoffman.com/TemplateGen.zip
Click to expand...

ConradH said:
The tone seems more high tech, but there are too many places where it can go wrong. The signal generator needed to be dead on frequency when they recorded it, and the cutting lathe needed to be dead on speed. Finally, whatever you're checking it with needs a good reference frequency and the software has to be bug free. All those things aren't that difficult, but too many steps are involved that you have no way to verify.

When you measure with a strobe disc or by timing, you're comparing the actual thing you want to measure, with a single reference time/frequency source.

Another thing to consider is wow. With a strobe disc it's easy to see brief variations, without losing sight of the overall drift. With a strobe disc off-center, you'll see wow from the error, but with it perfectly centered you can see what the table itself is doing.

With the timing method, you have the advantage of a very long test period and can get almost unlimited accuracy for the long term speed. Consider that any cheap quartz watch might be within a few seconds a week, which is a few parts in 604800, so the only practical limitation is how many revolutions you're willing to time to get an accurate number of seconds. It's actually the method I'd use as a reality check on any other method because there's so little room for error.
Click to expand...

OldSch00l said:
Yeah, I'm starting to think I should get either a strobe or possibly try the timing method....

For what it's worth, my phone is firmly positioned on the platter when I am using the RPM Calculator app. I suspect that each phone model's reliability is different regarding it's technical ability to accurately determine it's rotational speed using it's internal sensor suite. Which also leads me to question the accuracy and response of the microphone being used to measure the audible frequency with the PlatterSpeed app....
Click to expand...


The strobe disc/light thing was always close enough for me. The mix just struck me as funny. You are "OLDSCHOOL" by name, and yes you enjoy analog phono, but are new school enough to use digital phone apps for this purpose. Very interesting.
 
Just sayin, the Timeline can show speed deviations when an arm is lowered onto a record, its that sensitive.

I still don't have one but I wouldn't mind one.
 
I like strobe disk with neon or incandesent lamp better

because you can watch momentary fluctuations in speed, unlike stop watch or tachometer.
 
totem said:
Just sayin, the Timeline can show speed deviations when an arm is lowered onto a record, its that sensitive.

I still don't have one but I wouldn't mind one.
Click to expand...

Sensitivity and accuracy aren't the same thing. Just sayin'. ;)

John
 
KAB strobe/flasher

I've been using the KAB strobe and flasher system for a couple of years now. Because the handheld unit generates the flashes -it's independent of the mains . This seems more than adequately accurate for my purposes and is easily interpreted by the non-audio tech.
 
OldSch00l said:
After setting the speed of the table using PlatterSpeed and a 1K tone so that it is reading 33.3rpm, when I put my phone on the platter and use the other app - RPM Calculator - it tells me that the table is running fast (~34 rpm).

The question is, which should I trust?
Click to expand...

For such big difference, I'd do it the old way: Take one minute to count how many times the disc spins, using the label as reference. Assuming you use the label's top center as the rotation's starting point, 33 1/3 RPM equals 33 turns plus the top center of the label pointing at 4:00 on the next spin. Were we speaking of a difference of 1/8 of a spin, that would be a totally different story.
 
I just put a record on the platter... start up my iPad's stopwatch... and hope for 50 revolutions in 90 seconds. My Pioneer PL-15D consistently does 50 revolutions in 90.4 seconds. Good enough for me.


Sent from my iPad using Tapatalk
 
totem said:
Just sayin, the Timeline can show speed deviations when an arm is lowered onto a record, its that sensitive.

I still don't have one but I wouldn't mind one.
Click to expand...

Platterspeed measures speed down to 0,00286% variations. That fancy lamp will never do that.

Using DR Feickerts own test records this will be very precise some other test records I have used have been recorded at the wrong speed. But still its very precise.
 
You must log in or register to reply here.
Back
Top Bottom