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Challenging mic vs sensor with independent measurements

  • 1.  Challenging mic vs sensor with independent measurements

    Posted 16 days ago
    No app can self evaluate. The rep for the app cannot use the app to self evaluate. The data collected by the app must be subject to a higher authority measurement like Matlab. It is the only way to get an independent evaluation at a much higher level of accuracy. The app cannot do that.
    An electronic string sensor makes most of the apps tested so far reduce this variance as the app reports, but then the app itself has its own variance due to limited FFT length and window size and limited inter-bin measurement. 
    The particular app is not named because most of the tuning apps have a similar mic placement variance. 
    An app representative told me he saw no significant difference (?) in measuring his Yamaha C7 with the mic and then the sensor. That was simply uncorrelated with vast data I have already collected but not using his app. It also says, effectively, that his app is completely insensitive to mic placement variation, a statement that does not hold up, as we shall see.  
    I don't want to pit app against app. But I had to clear the air with this issue. It left me with no choice, but to do independently have someone conduct an experiment on a Yamaha C7 with his app.
    I had another well respected professional use this same app and go to a Yamaha C7 and take comprehensive measurements. He used 9 different mic positions per note and measured  C1, C2, C3,  C4, C5, C6, C7 and did a screen video recording of what App X was reporting and captured the .wav file audio so that I could then take the audio into Matlab to see what it actually is doing, and correlate it to that app.
    The app in this case could not resolve the variations in the spectra. The mic variance of the 4th harmonic, for example, of C3 was off by almost 1 cent. I typically looked at the first 5 harmonics in Matlab but have all the higher ones of course available. The C6 2nd harmonic was 9 cents off, yes that much. The C7 2nd harmonic was off by 19 (nineteen) cents. The upper register of the piano is literally filled with all kinds of false beats that show up in the spectra in matlab with great precision. We hear this junk with our ears also. The sensor is able to pick out the dominant one as previously shown in my video presentations.
    The app reported the following mic spreads. The actual was far worse with the same data evaluated in Matlab. In Matlab, the variances and ranges were significantly worse and wider than what the app reported, but the app had ranges as bad as 2 cents.
    The ranges as reported in the app were (C1 through C7);
    1.1, 0.66, 2.34, 0.46, 0.21, 033, 0.61, in cents!
    In Matlab the ranges were wider, depending on the length of FFT in the measurement. Since the FFT length and window functions and inter-bin calculations of App X were not known, there was no way of correlating in a general sense. I typically used 500 msec or 1 sec for the FFT length in Matlab. Most apps cannot handle this long so the variances are greater since the timeframes of the windows are less.
    Remember the sensor does not vary and this 'invariance' has previously been presented with extensive tests.
    Here are the details from strike to strike as reported by his app. Again, these are not my readings, but the readings of the app in question, and these were not done by me, but by an independent party.
    These are the mic measurements in cents offset from zero reported by the app:
    C1 = 1.1500    0.0500    0.1100    0.7000    0.5400    0.7000    0.6400    0.1900    0.2800
    Range = 1.1 cents 
    C2 = -0.8200   -0.7300   -0.8500   -0.4300   -0.6200   -0.1900   -0.7100   -0.6600   -0.5700
    Range = 0.66 cents
    C3 = 2.2500    0.3500    0.7300    0.4000    0.2400    0.3300    0.4200   -0.0900    0.0800
    Range = 2.34 cents
    C4 = -0.6100   -0.6800   -0.5500   -0.8400   -0.6600   -0.7400   -0.8900   -1.0100   -0.9700
    Range =  0.46 cents
    C5 = 0.1400    0.2300    0.2200    0.2700    0.0600    0.1000    0.1700    0.1900    0.2600
    Range =  0.21 cents
     
    C6 = -0.2900   -0.2600   -0.1700   -0.2400   -0.3000   -0.5000   -0.2600   -0.3700   -0.2200
    Range = 0.33 cents
    C7 = 0.9800    0.9100    0.5000    0.7600    0.8500    0.7600    0.4700    0.6400    1.0800
    Range = 0.61 cents

    More later, with spectral pictures to come.

    Best to all,

    Steve



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    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
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  • 2.  RE: Challenging mic vs sensor with independent measurements

    Registered Piano Technician
    Posted 16 days ago

    Have you ever considered Comsol Multiphysics as a platform for measurement?



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    Parker Leigh RPT
    Winchester VA
    (540) 722-3865
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  • 3.  RE: Challenging mic vs sensor with independent measurements

    Posted 16 days ago
    MATLAB is the international standard, de facto




  • 4.  RE: Challenging mic vs sensor with independent measurements

    Registered Piano Technician
    Posted 16 days ago

    Steve, the PianoSens is measuring frequencies emanating from the string while the mic is measuring frequencies emanating from the soundboard, how do you verify that the two are identical?



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    Steven Rosenthal RPT
    Honolulu HI
    (808) 521-7129
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  • 5.  RE: Challenging mic vs sensor with independent measurements

    Posted 16 days ago

    Points:

    1) Variance using the mic vs invariance using the sensor. It is an already understood phenomenon that moving the mic causes changes in the resolution process of determining an accurate reading of frequencies partials from position to position. 

    2) The actual reported variance by the app itself vs what the representative says the app reported. The independent study showed large variance in the app itself by moving the mic.  The representative cherry picked a few partials per note that lined up with virtually the same readings in the app with the mic vs the sensor to make it look inconsequential. It is already understood that some partials on some notes on some pianos will not vary much in frequency readings with mic positional changes, but some will. Now we have a statistical study that is needed. So an independent did a study and collected the data using the same model piano as the representative used. That study needed to be done in order to more comprehensively show the representative's results were not comprehensive and indeed were very consequential.

    3) In other words, if you are selling a $1000 app, it is in your best interest to say that there is no need to buy a $600 sensor in addition because it makes no difference. Well, the independent study shows otherwise. It is up to the reader to determine, from the numbers, whether it is consequential or not. It is not up to an app representative to do that. 

    4) The representative has dismissed a user for stating how much various apps were seeing significantly reduced jitter, by saying that the user was not experienced with apps and was not using his app. So what then happened? Later today you will see some new reports by this very user who gathered a room full of expert app users and evaluated this on a grand piano. Stay tuned (pun intended).

    Steve N.



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    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
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  • 6.  RE: Challenging mic vs sensor with independent measurements

    Registered Piano Technician
    Posted 16 days ago

    Steve, variance using the mic aside, was that an answer to my question? This test is using input from different sources, how do you verify that the composition -frequencies- of the two are the same? It seems that this would be essential for cross comparison.



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    Steven Rosenthal RPT
    Honolulu HI
    (808) 521-7129
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  • 7.  RE: Challenging mic vs sensor with independent measurements

    Posted 16 days ago

    Frequencies are set into motion as standing waves on the string, as they are the SOURCE. The soundboard and acoustic waves color this with up to 450,000 eigenmodes of spatial color (ref). The frequencies are not changing but the ability to discern and resolve them do change. Spectral analysis at the highest level is needed. 

    You still miss the most consequential aspect. You have significant variances with the mic. Which mic reading variant do you trust? Why? Is it consequential to YOU? If not, no need to keep debating. Just let it go. Just use your preferred app and your preferred mic and call it a day. I suggest you now let others write their findings, coming up today. Give some room for others, please. 

    Steve N.




  • 8.  RE: Challenging mic vs sensor with independent measurements

    Registered Piano Technician
    Posted 16 days ago

    Okay, thank you, the frequencies do not change at all during the transmission through the soundboard. I'll accept your word on that, out of genuine curiosity, how does one verify this?

    The reason it is consequential is that the ultimate arbiter is our ears, we don't hear the strings directly we hear what is coming out of the soundboard. I'm sorry that this so irritates you. But thanks for your answer.



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    Steven Rosenthal RPT
    Honolulu HI
    (808) 521-7129
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  • 9.  RE: Challenging mic vs sensor with independent measurements

    Registered Piano Technician
    Posted 15 days ago

    Steve R.,

    In theory (to follow your reasoning) , if you're using an ETD, you do not blindly follow the device and allow it alone to make all your decisions but rather you either check aurally as you go, or at some other convenient point to make sure device is working in line to what you want to hear. Why do you do you do this? Because computer algorithms and microphones do not perform exactly as our trained ears and brain perform. If you are using the thing as a "tool" and not a substitute brain, you likely find a need to make a few adjustments due to anomalies, etc. Alternatively you might make the decision to just "let it go" because it's not worth the effort to change it (IOW it's "close enough").

    So, you've already made the determination to "check" the electronics. The use of the sensor does not in any way change that. It simply eliminates (or greatly reduces) the introduction of "garbage" that might enter the ETD and color it's "thinking", giving the ETD a better chance at using its internal  capabilities to give you better answers and hopefully reduce the need to aurally correct it (but no claims are made that it will eliminate the need for checking). 

    So, arguments over supposed micro differences in frequency pickup at the string vs from the soundboard seem basically irrelevant (unless of course we simply want to argue for the sake of arguing).

    Feel free to argue the point I'm making. 

    Peter Grey Piano Doctor 



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    Peter Grey
    Stratham NH
    (603) 686-2395
    pianodoctor57@gmail.com
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