A Few Turntable Measurements using the RPM Android App

I should point out that the RPM app has not been independently verified for rpm accuracy. As I reported above, the repeatability is good.

The WOW 2 sigma reported by the app has also not been verified. In particular, the method of calculating the WOW has not been described. For example, is it the standard way of measuring? Is it weighted?

I can say that this app is good for comparing turntables and modifications to tables. The absolute accuracy of the reported rpm and wow is unknown. I would find it difficult to compare findings from this app to manufacturer's published measurements.

@ossicle2brain One way to find out how much weight is too much is to add weight to the table, then measure the RPM and WOW with the app. Continue to add weight until the speed changes or the WOW increases. This will probably happen before anything breaks.

But be aware. Too much additional weight may cause long term damage to the motor moving parts due to the increased load. It is very difficult to estimate that without long term measurements or manufacturer's recommendations.

@duckmanst3 Hi, I'm not questioning the accuracy of the hardware, although that would be nice to know. I'm concerned about the logic and math used to make the calculation. That info has not been published and probably won't be because (I bet) the person who created this app was doing it for fun, not for the rigor needed to develop a product for sale.

Yeah, using a phone for this measurement has little to no affect on the performance of the table.

Some belt driven tables take a long time to get to speed and settle, longer if weight is added. If he app starts before the TT has a settled speed, the measurement result will be invalid.

@ossicle2brain My Acoustic Sounds WOW XXL table is an excellent case. From a cold start, it needs a push on the platter rim to begin spinning.  One never knows when it is up to speed. There is no feedback. The REW app provides some idea. The app has a delay prior to beginning measurement. The WOW barely gets to speed before the measurement starts.

The motor used in the WOW has minimal torque, just the opposite to that of the Technics SL-1200  or the Denon DP-57L or DP-88.. I cannot think of a reason why AS decided to do this. I can't see an engineering reason.

@lewm I have not been able to find specs on the Nottingham or the Walker tables. It is quite difficult to make comparisons on table performance without basic speed and vibration specs. I will never buy a table again without seeing these specs.

One's ears are far less sensitive than the equipment used to measure table speed and vibration performance.

@terry9 Like with many quantities, the speed aspects of turntable rpm can be described as a mean surrounded by skirts on either side. I say this with trepidation, because the turntable noise is not a stochastic (random) phenomenon. It can have resonances, for example. However, narrowing the width of the frequency spread and diminishing the signal from resonant sources is a worthy goal.

Some say that a turntable that has poor rpm control cannot bring out all the nuance that a high end cartridge can pick up from an LP. This reason alone is why some people are interested in the stability of the RPM. The human ear is not a good instrument to evaluate rpm. One may prefer one or an other method of rpm control because the sound of one is more pleasing than the other. Comparisons based solely on listening is obviously important. This type of comparison is not quantifiable by nature. Specs are there to provide a guide to potential users.

Engineers develop a product based on numerical specifications that the company's sales and marketing generates. Engineers use test instrumentation to measure and compare design approaches. Without a formal methodology and explicit specifications, engineers do not know what nor how to build a product. And importantly, when to stop engineering and consider the problem solved.

Measuring performance parameters of instruments is crucial to product development.

Any company that does not report these values via a spec sheet is denying the customer one way to evaluate and compare different instruments. Some customers need to see these specs because they provide a baseline for the performance of the instrument.

Not publishing a spec prevents that from happening. Often known code words or phrases are used to appeal to the emotions of particular enthusiasts. These are not specs. Perhaps some don't care. I do.

@mijostyn The belt is brand new. Just put it on about a month ago. The old belt had stretched. The measurements I reported using the RPM app were done with the new belt.

 I was shocked by the poorer performance of the WOW. Acoustic Signature does not publish specs for speed stability, wow, flutter and rumble.

Seems that AS relies on the marketing of their special spindle material, the huge platter and the brass inserts to impress buyers. Must be good performance with all those buzz words, right. A simple measurement shows the difficulty of relying on bling rather than real measured performance. I was fooled. I bought it. One of my biggest audio gear mistakes. Won't happen again.

@brev Yah, it is fun making these measurements. I wish that the developer would publish his/her methodology. For example, what algorithm is used for the WOW calculation? Is it one of the standards?

I don't think we'll find out any time soon. Apps are usually closely guarded secrets.

But he/she could indicate which standard he/she is following, if any. Without this knowledge, it is impossible to compare RPM results to manufacturers' published performance.But relative performance between tables is valid.

@rauliruegas Hi, Thanks for the link. Surprisingly, the wow and flutter reported for the Double X by the author of the article you referenced is the same as the wow value I reported above for the AS WOW XXL using the RPM app. This result is encouraging, but not enough for me to trust completely, because the method of analyzing the data may be different.

There is no denying that the Double X measured wow value is 5x higher than the 0.02% I measured for the DP-57L table using the RPM app. Even more damning, the Double X it is worse than the wow reported for the Micro Seiki DD-40, an "entry level"  turntable.

The rumble spectrum is also quite informative. Although I can't make a 1:1 comparison with my (unpublished) results because gain and reference voltages may differ, I can say that the rise in noise from the 500 Hz baseline to the peak at 10Hz is about 60 dB for the Double X table in the article. I'm using the blue curve. This may be an incorrect trace, but there is no legend to indicate what the conditions were for each curve. My results indicate only a 30 dB rise for the DD-40. This is a 30 dB (30X) difference!!! Perhaps the region around the Double X was particularly high in vibration on the day of measurement. Or the line filtering in the Double X power supply is poor design or faulty.

One can also see the on the same chart a 50ish Hz peak.frequency. It rises 60dB above the baseline. The source is not identified, but is probably the AC line frequency. My measurements used a rumble track on the Hi-Fi News test record. The AC peak for the DD-40 is not visible, buried in the noise, which is already lower than the Double X.

It is very obvious now why Acoustic Signature does not publish these specifications. It could be very difficult to explain why a 70s "entry level" table beats their Double X for wow, flutter and rumble.

With all this now under our belt, can one say which table sounds better?

No.

But if one had to pick a table based on these results, the choice is clear.

I am also boggled to read that the reviewer summarized that the Double X performance as "high end".

How low do wow, flutter, and rumble have to be before they become inaudible in a "typical" listening situation? If the value is higher than that of every measurement result shown here, then the better performance of the DD-40 and DP-57L is not really needed. The Double X performance will be indistinguishable from those tables. But I think the answer is that since the manufacturer cannot control the conditions that a buyer will use its product, the manufacturer must strive to equal or beat the performance of the other "high end" tables.

If none of those publish these specs either, then my entire discussion is meaningless, since there's no way to determine from measurements which table is "better". Listening is always a very good method, but is usually highly compromised in any showroom environment. Perhaps listing is the only spec to test for. But how many people purchase a table without extensive listening to it prior to that purchase? I'd wager most do.

@terry9 There is a well-defined method for measuring wow and flutter and rumble, which only differ in frequency and source, but not in nature. This method turns out to be quite complicated. Whether the RPM app developer used this method or not is not disclosed. This makes comparison between published results and the RPM app results dubious. I do think that comparisons between tables using the same app (and phone) are valid qualitatively. That's why I feel sanguine about the comparisons I've made and reported.

If a manufacturer clearly states the method used (there are standards), then it can be used as a valid comparison between this table an others measured using the same method. It happened that I did measure the same wow 2 sigma as the spec sheet for the DP-57L and the DD-40. This may be coincidence. If a manufacturer does not provide a spec based on a standard protocol, then no valid conclusion can be made, obviously.

I find it difficult to believe that a manufacturer would not measure their product according to the well-accepted protocol. Engineering must have used some quantifiable method to characterize their creation. Engineers need a goal to reach. They need a goal that tells them that they've reached the goal and can freeze the design, stop development and move on to the next problem.Sales and marketing can decline to publish the results for a variety of reasons. Whatever the reasons, I feel a bit queasy without reported specs. I made this mistake with the WOW XXL. I will never do it again.

The test only goes to 200Hz. Any software and hardware (computer with A/D if chosen to do digitally) will have plenty of bandwidth (sample rate) to provide accurate results. The actual test uses a different frequency (3kHz or 3.15kHz), This frequency is detected, not speed. This makes the measurement more accurate because integration (averaging) times can be very short.

Implementation of the standardized protocol with all due attention to the accuracy of the test gear can accurately reproduce kHz frequencies. But only the errors that show up below 200Hz will be used to develop the result. If your hypothesis is correct, there is no method known today to capture errors from frequencies higher than 200Hz.The spec would have to change.

I have been in Engineering my entire career developing products for medical research, defense and communication at the highest level. What I've stated above is a part of how the development process works. Specs are designed so that they are measurable. If it is found that a method does not capture all the errors known, then the spec method is changed. Development cannot proceed without a measurable goal. In fact, turntable engineers may have an in-house spec to reach, knowing that meeting the in-house spec will guarantee that the industry standard method will produce the desired performance.

I don't presume to be an expert in measurement methods for characterizing turntables. I'm learning. Meanwhile, I call on my work patterns to inform me how I would proceed if developing a table. Differences in my approach to turntable engineers approaches may differ in details, but are the same in nature.

I do agree that some things are difficult to quantify. Turntable performance is not one of them. Whether one prefers this or that table is an emotional decision, a valid concern.Wow, flutter, and rumble measurements are quantifiable and repeatable (and agreed on).

@mijostyn I use REW for room characterization. It is freeware. The functions appear similar.

@terry9 Thank you very much! And thank you for joining in. I'm having fun learning how other real users think about audio and audio gear. I can't get that here in this countryside location.

Thanks to everyone else also.

@rauliruegas Thanks for the links. Great reading material. Seems like companies use whatever measurement protocol they feel is appropriate. This is very similar to the "alphabet soup" of specs that exist in the Optics and Electronics engineering world.

I thought about starting a new thread, but the conversation on this one is a good intro into my next question.

"How does one choose between belt drive (including string, fishing line etc...), direct drive and idler drive?"

There seems to be two crowds, direct drive vs all the others. I've had both. I had a bad experience with the AS table, but that could be an isolated problem. I really don't have a preference.

Very curious to hear ideas!

Is there any scientific data that indicates how a person with "normal" listening abilities perceives audio distortions? What are the lower limits or perception? Is there an emotional reaction to different frequencies?

The commonly accepted sating that "even order sounds "good" and odd order sounds bad" is ubiquitous. Is there scientific data to back that saying up?

If there are studies of this perception, I would really like to read references to that data.

I have difficulty accepting commonly asserted "facts" unless there is data that has been peer reviewed.

Pleas note that I am not bashing anyone. I am looking for explanations that are based on studies not commonly accepted sayings.

@rauliruegas  I would like to understand what type of studies have been made before I make the effort to design and perform the tests needed.

Since my last post I have been searching. I have found one (links below) that seems to be quite thorough and rigorous.

https://archimago.blogspot.com/2020/01/internet-blind-test-is-high-harmonic.html

http://archimago.blogspot.com/2020/06/blind-test-results-part-ii-is-high.html

http://archimago.blogspot.com/2020/05/blind-test-results-part-i-is-high.html

It may not answer all questions on this subject, but does provide some thought provoking results.

@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 @mijostyn 

Dolby is mass entertainment, not traditional music. I may be a :"wonderful" "immersive" experience, but it is not music.

This discussion has veered way off topic. Probably time to cap it off.

Thanks to everyone for contributing. I have learned quite a bit about how real audiophiles think about this great hobby. I'm not one yet. I may get there.

@rauliruegas I appreciate your willingness to continue this discussion.

However, I have learned much more than I needed from this conversation. I don't regret any of the comments made on this forum. For me however, the need for exchange of ideas has passed.

And I have have acted upon what I've learned.

A Technics SL-1200G Silver is on its way to me. I will have it this weekend.

This will be another learning experience for me.

This purchase is a direct result of your recommendation for "high end" turntables. I thank you for that great tip.

@rauliruegas I apologize.