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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.

kevemaher
mijostyn's avatar
mijostyn
8,570 posts
 

@kevemaher 

Trying to do anything over the internet is folly at best. There are way to many uncontrolled variables.

Most of what people say they hear is imagined which is why rigidly controlled studies with a cooperative panel are necessary to say anything.

All audio is personal. We all expect something out of our systems. I want to feel as if I am at a live venue. Needless to say I have never gotten exactly what I expect, close maybe, but not good enough which is why I am still at it. I am a lot closer than I was 25 years ago. This has nothing to do with the enjoyment of music. Most of my listening is done on an inferior workshop system. This is only about the potential performance achievable with todays tech at a less than ridiculous price,

@rauliruegas 

We seem to be like ships passing in the night. Are you saying that you can only achieve a satisfactory level of performance at a live performance and that this is not achievable with a residential system?  I attend a live performance about every other month. The last was Nickle Creek at the State Theater in Portland Maine about one month ago and it was killer. Chris Thile is a major talent. Their recordings are also stellar. Putting them in the media room is easy. Black Midi, not so much. 

All I care about is feeling like I am at a live venue. Many recordings make this impossible but that does not mean that I can not appreciate the voices of Billy Holiday or Enrico Caruso. With many recordings it is. System (includes the room) errors like sibilance and exaggerated high frequencies destroy any possibility.  Amplitude errors are far more pervasive then either IM or Harmonic distortion. What seems to bother me most with turntables is problems that interfere with pitch, more wow than flutter, things like offset spindle holes and warped records.  

mijostyn's avatar
mijostyn
8,570 posts
 

@rauliruegas , Only in instances of unamplified acoustic instruments are you going to perceive a real image at a concert. Many larger concerts have no image at all, they are mono. This does not mean that a stereo system can not create the illusion of real instruments before you. 

kevemaher's avatar
kevemaher OP
426 posts
 

@mijostyn I agree.Electronically shaped and amplified music at concerts is highly processed. It can sound really good or horrible depending on how it is set up. A home system should be able to beat an electronically amplified live concert easily.

Acoustic music, such as that created by a symphony orchestra, piano or organ in a large hall presents music in its natural form. It is difficult to reproduce this sound at home. Resonance induced colorations in a room at home are in the audio band. The resonances in a concert hall because of its size are mostly below audibility, but echo can be heard The concert hall is designed to damp reverberations. There may be poor sounding concert halls, but these are usually quickly corrected.

Music from home systems is highly processed also. We are at the mercy of recording and mastering techs. However, there are a small number of recordings that come very close to the concert hall sound. Solo piano and piano concerto recordings such as "Liszt - Piano Concertos No 1 and 2 Davis Decca VIV 11 (PHASE FOUR )" are my standards. I've found Arthur Salvatore's website, "High-End Audio" to be very helpful for choosing natural sounding LPs.

 

rauliruegas
13,384 posts
 

@mijostyn  : Btw, I attend for several years at least one day each week to listen live MUSIC.

  """ Are you saying that you can only achieve a satisfactory level of performance at a live performance and that this is not achievable with a residential system?  """

 

Obviously is not achievable in any room/system. Period.

 

Like you I like too the home system " illusion " ( fake ) that is central part of the home stereo reproduction but I'm not so anal about like you.

I wonder why you have not Dolby Atmos?

 

R.

mijostyn's avatar
mijostyn
8,570 posts
 

@rauliruegas 

Dolby Atmos? Come on Raul, that stuff is for Mexicans:-) 

What I am saying Raul is only unamplified acoustic instruments present us with a realistic sound field. Everything else is compromised to one degree or another. A great home system is more capable of presenting a realistic impression than the majority of amplified venues. 

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