A Few Turntable Measurements using the RPM Android App

I found this Android phone app for TT rotation. Phone is Pixel 4a. Thought I'd try this app out. I'm skeptical of these phone apps. Accuracy is always an issue.

I have four tables. I took 5 readings for the first table in order to see what the repeatability is. The "absolute" RPM, RPM peak to peak, and 2 sigma  range readings were very, very repeatable. Consequtive RPM readings differed by a max of  0.01 RPM. Two sigma varied by 0.01% ( 2 sigma means that 86% of the readings were within the stated value). I personally would use 3 sigma, but that's a personal quibble.

I've measured all four of my tables. I am very certain that the results are very repeatable. I measured with no LP, LP rotating,  LP on and Stylus engaged, and phone offset from center. RPM was the same for all cases, The 2 sigma showed a  0.01% rise (really small). The reading at the edge of the LP was different. And scary to do!

Here's the results:

1. DD-40 #1, RPM = 33.32,  2 sigma = 0.07% (63 dB)

2. DD-40 #2, RPM = 33.27,  2 sigma = 0.09% (61 dB)

3. Acoustic Signature WOW XXL, RPM = 33.17,  2 sigma = 0.10% (60 dB). This varied 0.02% from reading to reading (after running the table for 10 minutes, this noise diminishes), but the 2 sigma stayed the same.

4. Denon DP-57L, RPM = 33.25,  2 sigma = 0.02% (74 dB).


I then went back to DD-40 #1. Using the RPM app, I set the mean speed to be 33.25. The strobe on the table was slowly moving! I checked against the strobe on the Cardas test LP and yes, the RPM speed accuracy was wrong. I reset TT speed using the strobe. The RPM app measured 33.23 again. I must conclude that although the RPM app is very repeatable, the absolute accuracy is not. The wow result (2 sigma variation) remains the same.


I measured the 45 RPM on DD-40 #1. RPM = 44.91, 2 sigma = 0.05%, so the 45 RPM is fairly accurate and the 2 sigma is lower.


This app makes no distinction between wow and flutter. It's all reported in the wow reading (wow and flutter are the same thing by nature, the only difference is the frequency range).


I'm surprised by the poor performance of the WOW XXL table. This a modern, belt driven table, with a massive platter. It is 5 years old. There's no way for the user to adjust the RPM. The variation in the speed is similar or slightly higher than the 40+ years old Micro Seiki DD-40 tables, which don't have crystal oscillator driven speed control. The WOW XXL takes about 10 minutes before the very high frequency variations settle. Now, I don't know much about the internal workings of the app. Helpful would be better accuracy (or the AC frequency in my house is not 60 Hz). Bandwidth is not reported.

The DP-57L performance is outstanding!. This TT was made in the 80s. And the DD-40 tables are not bad, but are as good as or better than the WOW XXL.

In summary, in my opinion, the RPM Android App is very useful. The absolute accuracy is a bit off, but the repeatability is very good The wow measurement is also quite good.

128x128Ag insider logo xs@2xkevemaher

The Wow XXL does have adjustable speed, but it is not well documented.  There are 2 tiny buttons on the back of the table.  Each push of a button will either slightly raise or lower the speed.   I don't recall which button raises or lowers, so you will have to experiment.  This won't change variations, but at least will allow the RMP to get closer 33.33. 

Dear @kevemaher  : Good that you shared those measurements that speaks by it self what I knew of the Denon quality.


I still own two Acoustic Signature old top of the line TT's alog Denon, Technics, Luxman and the like. Inside the external PS in my TT's I can fine tunning its speed and you can do it with your table too:


"" The Wow XL is driven by an ultra-precise synchronous motor that employs a 20MHz microprocessor that provides “perfect” speed stability and fine-tuning. Two small recessed buttons on the back of the ’table allow ±0.1% speed adjustments, so you can dial-in the speed during initial setup. I checked the speed after I set up everything, and it was spot on. I checked it three weeks later, and things were still spinning correctly. It’s safe to assume that once you initially set the speed, you can leave it be without worrying—it’s always good to check speed if you move the ’table, though. The motor is extremely quiet, too. Fitting the belt was easy, and once the motor was turned on any twists were straightened out after a few revolutions. Two stainless-steel buttons are located to the left of the platter, an on/off button and a 33/45 button to easily switch speeds. Turn the turntable on, and a red LED blinks above the speed button until the precise speed is reached.  ""



Regards and enjoy the MUSIC NOT DISTORTIONS,


I have to say that the RPM app should be bought before you spend a lot on a strobe. I have the manual Clearaudio Device - its' good but the App is just so consistent and sensitive. I used a spray can lid to place my phone on when i use the app (for decks without a weight with a flat top). Slightly off-topic but i very much doubt that the phone weight will skew the reading once the deck is up to speed what say you guys


My concern is that the weight of a cell phone placed eccentrically on the platter will per se skew the reading, especially for wow and flutter. Furthermore, is there independent evidence that the rpm readout is accurate? I thought there was some doubt about that. Repeatable, perhaps, but accurate to for example +/- 0.1 rpm? Or even +/-1.0 rpm? I dunno.

I can’t see how a small off center mass would alter the wow and flutter.... if the platter is level. But like "animal" above I also use a small plastic bowl over the spindle so the phone can be centered.

The app I’m using is called RPM speed and wow. Fun stuff. I used it to gauge how well my fishing weight platter mod worked. I glued four four oz lead fishing weights around the perimeter of the platter. I was careful to balance it by teetering it on a marble. Then I used the app to see the change. Went from 0.18 to 0.14 with the extra pound. Platter went from a massive 2.4 up to an incredibly heavy 3.4  pounds!  🙄  The table is a Music Hall 2.3, so fun to mod, and it needs it.