Pianotech

Expand all | Collapse all

Dispelling the 'Myth' of the Missing Fundamental

  • 1.  Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-22-2024 03:17
    • Dispelling the 'Myth' of the Missing Fundamental
    • Video Presentation YouTube Link: 
    • https://youtu.be/Gj0xobcBpdM
    • There is a widely held 'myth' called 'the missing fundamental' in the bass register of a piano. 

    • * This myth is very unfortunate and very untrue.
      * I am here today to dispel that myth once and for all with irrefutable evidence. 
      * Is the fundamental present all the way down to A0. Of course!
      * This evidence was collected from a PianoSens sensor on a large concert grand, a Fazioli F308. However, I did a similar experiment over 15 years ago using an instrumentation quality microphone on a Steinway D and got a similar result.
      * As you watch the video and hear the explanation, you will clearly and unequivocally see that there are clean, pristine periods of repetition at the fundamental frequency all the way down to A0. 
      * You will see the spectral view of the time domain showing that the fundamental A0 is down only 9 dB from the 2nd harmonic A1. A factor of 9 dB is still very easily heard by human perception even at that frequency.
      * I also show just how 'messy' the transient response is from the hammer strike moment, compared with the PianoSens sensor.


    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------


  • 2.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-22-2024 06:25
    Interesting discussion. What I have always understood is that "missing fundamental" refers to the challenge that the soundboard faces in radiating these low frequencies, not the strings. When you realize that the wavelength at frequencies below 30 Hz is more than 10 meters, you can imagine that.




  • 3.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-22-2024 07:59

    Yes, this is very interesting. 

    Chris Chernobieff has demonstrated to me that the base frequency of a soundboard (new or old) is around 49hz (Chris, correct me if I'm wrong here).

    Is it possible that the string is in fact generating the fundamental but the soundboard simply is not amplifying it? And as noted, the smaller the piano the worse the situation?

    It would make sense that the pianosens pickup could detect it whereas the mic would not.

    Peter Grey Piano Doctor 



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



  • 4.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-22-2024 09:58
    Hi Peter,

    As I stated in the video, I did this years ago on a Steinway D with a really mic having a flat response below 20 Hz. I placed the mic very close to the lowest string. As you know, the string is so skinny compared to the soundboard that it doesn’t make much sound, because it cannot move much air. I still got a spectral component of the fundamental, and still saw the repetition in the time domain of the fundamental frequency. it was not as strong as it was on the Fazioli. It was down more than 12 dB but still present.

    Respectfully,
    Steve




  • 5.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-22-2024 10:05

    Ahh yes...I forgot that point. 👍 

    Edit: Would be interesting to try this on a PSO (piano shaped object [not the other one]) 😉 

    Peter Grey Piano Doctor 



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



  • 6.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-23-2024 23:24

    Thanks for the Honorable mention!

    Yes, my tests have shown that most soundboards are between 49-51 Hz on average. Some have been as high as 60 hz. I believe now that they should be 55 hz and no one has ever figured out how to get them at that frequency or perhaps even tried, which is what i am developing at the moment.  55 hz is obviously important as it will put the board at the same harmonic/overtone series when a piano is tuned to A- 440, Consequently you would want a board to be at 54 hz if the instrument is going to be tuned at A=432 etc.  Interestingly enough, its also possible that when they are first crowned the hz is high, then as they age the pitch comes down eventually to 55hz and then the piano has that great broken in sound. 

    Back to the Lab,

    -chris



    ------------------------------
    Chernobieff Piano Restorations

    "The Piano Whisperer"
    Maker of the finest maximum output piano soundboards. (Osage Orange Bridge Caps, Norway Spruce Panels, Engineered Ribs, Sustain Bar)

    Inventor of Inertia Touch Wave (Real Dynamic Inertia Control and Smoothness)

    865-986-7720 (text only please)
    ------------------------------



  • 7.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-22-2024 13:41

    • There is a widely held 'myth' called 'the missing fundamental' in the bass register of a piano. 

    Really? Missing? Where did you learn about this? I always thought it was well a known fact that while the fundamental in the lower bass register is of such a low level as to be unusable, (in tuning), and usually inaudible in performance, it has, nevertheless, always been there. 



    ------------------------------
    Geoff Sykes, RPT
    Los Angeles CA
    ------------------------------



  • 8.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-22-2024 13:52

    Geoff, the top tech at a major conservatory (don’t want to name him) has a whole lecture on how the fundamental is missing. He has a lot of credibility among piano tuners. I showed him this and he was ‘amazed’. Also, ‘every tech’ I have know over the years believes this ‘missing fundamental’ myth. I have encountered a top ETD maker who also sweared that the fundamental is missing. Again, I showed him this. He still reallywas not convinced and just 'excused' it as a result of the sensor's ability to pick up the string movement. I then told him about my old experiment years ago on the Steinway D using a mic. I think if one uses a mic, one must capture the string very close and capture some of the air movement of the string. Perhaps only the largest concert grands have a soundboard large enough to capture anything at all. However, one must do this offline with high resolution FFT windows, my specialty of course. Maybe it is just the people I have cited and hung around who believe this and maybe every other tech believes like you. I don’t have a statistical group survey, ha ha ha!




  • 9.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-22-2024 14:07

    Just google 'missing fundamental piano' and a lot of things come up

    Here is one from 2010 on PianoWorld. https://forum.pianoworld.com/ubbthreads.php/topics/1790672/1.html



    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 10.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 00:12

    You are correct, Geoff, that it was not universally assumed to be entirely absent.  For example, in Physics of the Piano, Nicholas Giordano does indeed refer to it as "the missing fundamental", but in the text itself he makes it clear that the fundamental need not be gone entirely, just weak enough to be "essentially inaudible".  Rather, he uses the term in reference to the phenomenon that human hearing will perceive a note at the fundamental frequency even when that frequency is missing or very weak:

    if the fundamental component of this tone [A0] is so weak as to be essentially inaudible [emphasis mine], why do we perceive the pitch of this note to correspond to that of the missing fundamental at 27.5 Hz? Why don't we perceive the pitch of this tone as 55 Hz, corresponding to the very weak second partial, or 82.5 Hz corresponding to the somewhat stronger (but still weak) third partial?  This is the puzzle of the missing fundamental.

    The phenomenon of the missing fundamental has been known for nearly two hundred years, and has gotten the attention of many well-known physicists, including Georg Simon Ohm, . . . Thomas Johann Seebeck . . . and later Helmholtz. The way we perceive tones with weak or missing fundamentals has been clearly established through many listening tests, making this a case in which the perception of musical tones can teach us something about how humans sense pitch.

    This is on pages 130-131 if you want to read the rest. So I think what we have here is just a misunderstanding (perhaps widespread among piano techs) of what was really meant in the first place by "missing fundamental". The point, at least the way Giordano tells it, is that we have the ability to perceive missing or weak fundamentals based on higher partials -- not that the fundamental is truly missing in the low registers of the piano.



    ------------------------------
    Nathan Monteleone RPT
    Fort Worth TX
    (817) 675-9494
    nbmont@gmail.com
    ------------------------------



  • 11.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 09:22

    Nathan wrote: "So I think what we have here is just a misunderstanding (perhaps widespread among piano techs) of what was really meant in the first place by "missing fundamental". The point, at least the way Giordano tells it, is that we have the ability to perceive missing or weak fundamentals based on higher partials -- not that the fundamental is truly missing in the low registers of the piano."

    There is a simple, low tech demonstration of this. Equipment needed: Handkerchief, tape measure, house keys, one grand piano with lid open.

    1) Measure and determine the midpoint of A0.

    2) Raise the damper of A0 and hold it up (sostenuto pedal).

    3) Wrap the folded handkerchief around a fingertip.

    4) Press down A0 at the midpoint.

    5) Lift hand quickly, setting A0 into motion in its first mode.

    6) What do you hear? Anything?

    7) While the A0 is still visibly moving, touch with the loosely held house keys, lightly and quickly, near the strike point of the string.

    8) What do you hear?

    Comments: The piano has little capacity to transduce a 27.5 Hz vibration into sound waves, and the human ear has limited ability to transduce a weak 27.5 Hz signal into a perceived sound. (You might try biting the piano rim or plate to test if you can hear more by direct conduction.)

    The production of difference tones is a fun game to play with flutes or recorders. Any two notes that represent adjacent partials of an overtone series can produce a "faux" fundamental. Playing 18th century French flute duets, I've been nearly convinced that the "faux bass line" was an intended compositional effect.

    A response curve of human hearing shows our lesser ability to hear at lower frequencies. The difference tone of higher partials is necessary to "hear" the fundamental...whatever "hear" means in this case. Look at the relative effort required to play forte tones on a violin or a double bass.



    ------------------------------
    Ed Sutton
    ed440@me.com
    (980) 254-7413
    ------------------------------



  • 12.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-23-2024 09:02
    I have always assumed that A0 has a fundamental and the myth hasn’t penetrated to me, anyway. My understanding is that the fundamental of A0 is so weak compared to its higher partials that it is pretty inaudible. In organ building a 32’ pipe is needed for the fundamental of A0 but the combination of a 16’ and and 8’ pipe can give the illusion of hearing A0. I expect I’ll hear about it if my understanding is wrong.

    Bob Anderson, RPT
    Tucson, AZ




  • 13.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-23-2024 09:59

    There will always be a fundamental.  The question is what is the relative strength of the various partials.  Steinways have well balanced fundamentals at A0

    Mason & Hamlins even more so.  Bosendorfers go lower but their fundamental is relatively weaker.  Many other pianos fall between these extremes. A

    grand piano with a substantial hardwood rim or an upright with a strong back construction will generally have a stronger fundamental.



    ------------------------------
    Parker Leigh RPT
    Winchester VA
    (540) 722-3865
    ------------------------------



  • 14.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-23-2024 11:01
    The interaction of two frequencies that differ by a perfect fifth, i.e. with a ratio of 3:2, will produce a subharmonic an octave below the lower note. If you tap out the 3:2 rhythmic pattern, you'll notice that every third impulse of the 3 frequency coincides with every second impulse of the 2 frequency, reinforcing or strengthening it. This reinforcement generates/is a real impulse at 1/2 the fundamental frequency of the lower pitch, one octave below it. 
      I think if you sound a pipe at half the length of the lower pitch, there is no partial from the shorter pipe whose frequency is 3/2 the fundamental of the longer pipe to generate the suboctave. 

    Mark Schecter
     | |   | | |   | |   | | |   | |   | | | 






  • 15.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-23-2024 13:48

    Mark,

    A 'subharmonic' does not exist in a linear process because what you describe is not an actual spectral component if you do a Fourier Transform of the waveform. The only way it can be a spectral component is a nonlinear system, wherein two harmonics are 'mixed' or effectively multiplied together as in modulation, creating actual sum and difference frequencies from the modulation.

    Steve



    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 16.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-23-2024 19:12

    That is why I often use the fifth as a reference whentuning the low bass.



    ------------------------------
    Parker Leigh RPT
    Winchester VA
    (540) 722-3865
    ------------------------------



  • 17.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-23-2024 20:06
    Parker, better yet, use the 12th, not the 5th. —Steve




  • 18.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-23-2024 21:06

    For tuning the lowest notes on a nice piano, since I am tuning 12 TET based on the octave (i.e., ET), I will often start with a double octave for initial placement. Then testing with a progression of seventeenths (5:1), and on a good day I can also bring in minor sevenths (7:4) or minor sixths (8:5) as additional testing and with their slightly improved accuracy over the seventeenth..

     

    Mark, resonance works well going from a string that is partial #2 or #3 (as well as higher partials) down to the fundamental string. But for me the strongest resonance created is always equal to the partial in frequency. Maybe with non-linearities the fundamental might also be there, but much reduced in amplitude. Regards, Norman.



    ------------------------------
    Norman Brickman
    Potomac Piano Service
    Potomac, Maryland
    potomacpiano@verizon.net
    https://potomacpiano.com
    (301) 983.9321
    ------------------------------



  • 19.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 00:29

    Peter has 'challenged me' indirectly (ha ha) to do the A0 with my Neumann KM183 mics. Then I use the same parameters of Matlab as I did before when I captured the A0 with the PianoSens sensor.

    The pic is below. Double click it to see it better. The top view is amplitude vs time. The startup is messy compared with my prior presentation using the sensor, but there are still very clearly defined periods of A0 that I have marked.

    Now look at the spectral view on the bottom. Look at the 3rd and 6th levels as the highest of the first 10 harmonics, but look at the fundamental which is only 5 dB below the 2nd harmonic. Amazing. So, it all boils down to how to set up the experiment and how to perform the frequency analysis.

    Best,

    Steve

    A0 with Mic


    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 20.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 14:41

    Colleagues, 

    There is big difference between 'acoustics' and 'psycho-acoustics'. There is a big difference between what we 'think' is so, and what we can 'measure' as so!

    Some things are hard to find evidence of, but we know to be true, but the best is when there is some evidence so that it is not 'blind faith' but 'evidence-based' faith. It is my job to base every statement on actual evidence that is non-contradictory to all other evidence. 

    For example, I posted above the evidence of measured data of the harmonic levels of both the sensor data (the original post and video that started this) and microphone data (last night and above post) of the first 10+ harmonics of A0, showing both the time and frequency domain. The measured harmonic magnitude levels were different due to the EQ of the two pickup devices, but both showed the full evidence of the presence of a significant level of A0 fundamental. If you google 'missing fundamental' there are lots of hits and this is what started me on the venture for the post. I am glad I took the time to actually make the measurements and post the data.

    I explained in an earlier post that there is no such thing as a subharmonic in reality unless there is an actual spectral component, which cannot come from a linear system but it can come from a strong non-linearity that creates a spectral component that is the result of the subtraction and addition of two frequencies.

    Hope that helps!

    Respectfully submitted,

    Steve



    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 21.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 15:10

    I was arguing that the term "Missing Fundamental", used correctly, referred to a psychoacoustic phenomenon in the first place -- not an acoustic one.  Wikipedia seems to agree with me as well, for what it's worth: Missing fundamental - Wikipedia

    Wikipedia remove preview
    Missing fundamental - Wikipedia
    A harmonic sound is said to have a missing fundamental, suppressed fundamental, or phantom fundamental when its overtones suggest a fundamental frequency but the sound lacks a component at the fundamental frequency itself.
    View this on Wikipedia >

    .

    I don't doubt that some piano technicians have gotten this mixed up, even prominent ones.

    (edited to fix the wikipedia link)

    ------------------------------
    Nathan Monteleone RPT
    Fort Worth TX
    (817) 675-9494
    nbmont@gmail.com
    ------------------------------



  • 22.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 15:15
    Nathan, I cannot emphasize enough the importance of evidence-based data in these discussions. Without evidence-based real data and precise measurements, all things devolve into endless debate. —— Respectfully, Steve




  • 23.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 15:18

    I don't follow. Do you feel like I'm not providing enough evidence as to what the correct interpretation of the term is?  Do you mean that you want to see evidence of the legitimate psychoacoustic phenomenon?



    ------------------------------
    Nathan Monteleone RPT
    Fort Worth TX
    (817) 675-9494
    nbmont@gmail.com
    ------------------------------



  • 24.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 15:27

    Not anyone specifically. Take no offense, please. I don't think many understand just how much work it is to make engineering tests / measurements and explain the results in precise language. Engineers usually get paid handsomely to do this kind of work in commercial and military fields with a paying customer. The quality of my work I post is at that level because I have been doing it for major customers for 40 years. I am doing this signal processing research on piano, only because I want to educate serious PTG members who want to learn about the subject. I post things that we normally cannot find in the prior piano research journals. I am just giving away the time and effort. I do hope one day people appreciate it. It distracts me from my current paid customer tasks and sometimes I just think it is falling on deaf ears and I should just stop and go back to my professional signal processing work.




  • 25.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 16:21

    @Steven,  I didn't see this message when I wrote my post below, so I hope you don't take that as being an unappreciative response. I've enjoyed watching your videos and reading your posts, and I appreciate being confronted with new ideas that challenge my current understanding. 



    ------------------------------
    Anthony Willey, RPT
    http://willeypianotuning.com
    http://pianometer.com
    ------------------------------



  • 26.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 16:38

    So, I think there's a couple things that really might ease your path if you acknowledged them.  First, you're not the only person in here with an engineering background, who could be making more money doing something else.  Second, if you really stuck to posting hard data as you advocate, I think you'd see a lot fewer protests.  The problem, for me, comes in with claims like
     * "There is a widely held 'myth' called 'the missing fundamental' in the bass register of a piano." (I've tried to explain that "the missing fundamental" refers to something different than assumed here.)
     * "So let's say your standard deviation error is 0.5 cents from acoustic interference. The square root of 88 is 9.38, so if you have increased the probability of the spread of out-of-tune-ness by at least 5 cents or more." (This is simply incorrect, that's not how standard deviation works. I tried to gently explain that but you then claimed you were uninterested in talking about statistical models.  Why did you present one in the first place then?)

    Again, I think your device is interesting, and I think several of your findings are interesting.  But I don't think it's in anyone's best interest for me to ignore it when I spot something in a claim that looks incomplete or incorrect.  I think we can learn a lot from you here, but I think you can learn from us too if you're willing to listen.



    ------------------------------
    Nathan Monteleone RPT
    Fort Worth TX
    (817) 675-9494
    nbmont@gmail.com
    ------------------------------



  • 27.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 17:17

    Nathan,

    Please send us your resume bio. I have attached mine. Obviously you want to keep hammering me on the square root of 88. I more than clarified the variances by another means. You are ignoring my clarifications. So I guess I have no choice but to refer you to my bio. I have attached it. We can compare.

    I am being hammered. Take my responses that followed as the right answer. I welcome your data you will be collecting, your signal processing insights and analyses, and your conclusions from your actual data. I welcome your statistics you will be gathering, the actual variance measurements, the spectral analysis on the interferences and the window of the FFT and your FFT intra-bin algorithms you will describe that show the PPM of the intra-bin accuracy, and many other things that you have great expertise in. We need more people like you doing this work. We need highly credentialed signal processing engineers with books, papers, patents, so that we can trust their work output. If you have these skills, I welcome that. I have an MIT professor friend who is probably the top person in the DSP field, a pioneer, checking my work. So far he approves 100%. Nice to know. We were colleagues back in the 80’s when DSP and high quality spectral analysis was being invented at Bell Labs and MIT. I was in the DSP department at Bell Labs and he was at MIT.

    Best,

    Steve

    SRN Bio





  • 28.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 17:33

    Nice try, but I fear my background is far humbler than yours.  And yet I was still able to find and demonstrate an error in your math, and point out something you missed w/rt the correct meaning of missing fundamentals.  If you require extensive credentials before you're willing to listen to such simple corrections, I simply cannot provide them.  Have a nice day.



    ------------------------------
    Nathan Monteleone RPT
    Fort Worth TX
    (817) 675-9494
    nbmont@gmail.com
    ------------------------------



  • 29.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 17:39

    Hammer me forever without reading my clarifications. Get your own MIT DSP professor to review my work and my replies, I will then listen. What if I simply declare to the world out loud that I was only trying to show how the Gaussian Curve would give us more and more outliers with larger numbers of notes? Yes, the square root of the variance is the standard deviation. The standard deviation is also the RMS value. The RMS value comes from a significant number of measurements. There is an old expression “Torture people until they cry ‘uncle’. What are you trying to prove? That on a small technicality that was more than clarified, that you sill relentlessly not let to until the 'big boy' cries 'uncle' and then you can strut around saying you took down the big boy? Is this all about some ego thing? 

    HERE is what I propose you do. Start taking your own measurements and set up a great methodology of experiments. Take the data into Matlab. Show us your algorithms and describe your experiments. Then I will more than gladly welcome your engineering expertise and painstaking work. 

    Respectfully 

    Steve






  • 30.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 18:39

    Steve-

    Piano technicians are simple folk trying to support themselves practicing a rather antiquated trade in a shrinking corner of a musical world that is rapidly changing. Most of us do not understand at your level of detail what you are writing about. We see the streaming arguments and think "Enough."

    If you have invented something that can help  our work, demonstrate and communicate clearly how to use it within the constraints of our daily work and you will soon have a group of eager followers, happily promoting your product. Learn from your friend Frank I. how he developed PianoScope through extended communication with piano technicians.

    This would be very helpful to your potentially much larger audience.



    ------------------------------
    Ed Sutton
    ed440@me.com
    (980) 254-7413
    ------------------------------



  • 31.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 19:23
    Ed,

    My video on False Beats is a very good example.

    My video on frequency invariance is a testament to having a reliable method.

    My videos ARE a testament to how a tuner can get better results.

    My videos on how one can tune string by string the unisons IS the killer testament and the cornerstone of the invention. Carl Lieberman himself said that is a GAME CHANGER.

    I rest my case.

    Steve




  • 32.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 20:09

    Steve --

    I know I said I'd keep quiet and just watch for a while but...

    > "Is this all about some ego thing? "

    You a funny guy!



    ------------------------------
    Geoff Sykes, RPT
    Los Angeles CA
    ------------------------------



  • 33.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 20:23
    Thanks, Geoff. We all need to examine our hearts and ask ourselves “how should we communicate” in a way that endears us to be open and say it with love and respect. I appreciate your remark! —Steve




  • 34.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 16:15
      |   view attached

    Ed Sutton wrote, "The piano has little capacity to transduce a 27.5 Hz vibration into sound waves, and the human ear has limited ability to transduce a weak 27.5 Hz signal into a perceived sound." This hits the nail on the head in my opinion. I don't think anybody is saying that a (roughly) 27.5 Hz wave doesn't exist on the vibrating string of A0. It clearly does. But it's unimportant enough that we can ignore it. 

    Just for fun I recorded A0 on my Yamaha U1 using a ~$100 AT2020 condenser mic. (Not recording studio equipment, but probably better than most human ears) Here's the frequency spectrum, plotted on a dB scale. 

    You can find a 26.8 Hz "fundamental" peak about 27 dB below the strongest "4th harmonic" peak, which is something like 7-8x softer. But that doesn't take into account the human perception of loudness. Even if the fundamental were as strong as the 4th harmonic, we humans would still hear it around 40-50 "phons" softer. There's no point IMO in trying to tune a harmonic that no tuner, pianist, or audience will ever hear. 

    Another consideration: a couple people have mentioned difference tones...that we can perceive a 27.5 Hz tone even though the first harmonic is basically absent. Those difference tones come from the interaction of higher harmonics, and those higher harmonics are more widely spaced than lower harmonics because of inharmonicity. In fact, when I take the autocorrelation of the FFT of my sample, I find a peak at 27.6 Hz, a full 48 cents above the "fundamental" frequency of 26.84 Hz. Admittedly I'm out of my depth here, but I would speculate that the difference tone would be more audible than the fundamental. 

    To be clear, I'm excited to try out Pianosens for several reasons. Detecting the missing fundamental isn't one of those reasons. I'm more excited about being able to ignore the leaf blower outside, which, of course, was present when I made the attached recording. 



    ------------------------------
    Anthony Willey, RPT
    http://willeypianotuning.com
    http://pianometer.com
    ------------------------------



  • 35.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 19:44

    Here are a couple of papers from the Journal of the Acoustical Society of America that may be related. The ASA has a deep reservoir of quantitative analysis of different aspects of sound production in pianos. Here and here



    ------------------------------
    Steven Rosenthal RPT
    Honolulu HI
    (808) 521-7129
    ------------------------------



  • 36.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 20:09
    Hi Steven,

    Most of the prior art does not take into account the ‘linear’ and the ‘nonlinear’ aspect of the harmonic analysis. Perhaps you saw my explanation on the nonlinear aspect which causes the sum and difference frequencies, whereas the linear model does not cause this sort of modulation.

    I’ll check them out.

    Thanks.

    Steve




  • 37.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 21:18

    Steve, I've seen you refer to it but I missed the explanation. Would you refer me to that or tell me what you mean by "linear model"?

    The first paper does say that the so called phantom partials are largely due to the non-string components of the piano.



    ------------------------------
    Steven Rosenthal RPT
    Honolulu HI
    (808) 521-7129
    ------------------------------



  • 38.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 21:34

    Sure. A nonlinearity between two harmonics can be modeled as a multiplication or modulation. Say, if you had a 200 Hz and 300 Hz frequency superimposed, they would not create a 'subharmonic' of 100 Hz in a linear system. In a non-linear system, the 200 and 300 Hz signals would be multiplied and create 'sum and difference' frequencies, so you get get a 100 Hz and 500 Hz modulation sidebands! Very small non-linearities would result in very small components at 100 and 500 Hz. That would be called the 'modulation index' or factor. Best, Steve



    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 39.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 21:16

    Hi Anthony,

    Thanks for collecting the data above. I sent you a private note on this and it may be something others want to use so we have apples to apples. I use the start of the FFT at the zero crossing before the first initial peak value sample. I usually use 1-second-long FFT. Try to collect the data with a great omni mic that has a -3dB point at or below 20 Hz. You could add +3dB to the 27Hz value for example. I have a couple of Behringer mics that I am no longer using them so if anyone wants them I can sell them. I place the mic as close to the string as I can and try several locations along the string and compare. The string does not move much air but every little bit helps.

    Try getting access to a great 9' concert grand like a Steinway D. You should see a large improvement of the lowest harmonics.

    There are folks who think this is all irrelevant to real-world tuning. Partly true and partly not. The sensor has such a better organized initial transient in the first 120 msec, if you look at the original post and video I made. The more organized structure of the sensor tells us a lot about what we can 'trust' more.

    Your sensor is shipping out next week!

    Best,

    Steve



    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 40.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 21:30

    Here is an apples for apples comparison on C2. The first 50 msec transient startup in the time domain. Look at how messy the situation is acoulstically with the mic vs the sensor. There is nothing wrong per se with the mic. It is the string getting the whole acoustic 'system' going in the bridge and soundboard that is making things incoherent. This has been what we use up to the current date for feeding our ETD's. Every pickup point of the mic will have a different view and hence a different representation to the ETD. The frequency peaks of the underlying waveform are still there but harder to discern with a mic or with the human ear, causing large variance position to position.

    Double click on the image for a better close up view.

    Respectfully submitted,

    Steve

    C2 transient startup


    ------------------------------
    Steven Norsworthy
    Cardiff By The Sea CA
    (619) 964-0101
    ------------------------------



  • 41.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Registered Piano Technician
    Posted 01-24-2024 22:28

    Steve, okay, so by linear, you mean the signal of the string alone. I get that the linear signal is clearer, certainly more ETD friendly. But are you saying that the signal modifications caused by the acoustic 'system' aren't relevant or need to be accounted for?  Don't the non-linear signals affect the audible beats? Not so much for tuning unisons, but for finding the right interval relationships in tuning the piano as a whole, temperament, stretch, etc. Your assertion is that all the necessary information can be derived from the linear model. As you say, the end result is non-linear, it's not a 1:1 relationship between the signal of the string and the audible signal of the piano. Not trying to be argumentative, I just don't understand. 



    ------------------------------
    Steven Rosenthal RPT
    Honolulu HI
    (808) 521-7129
    ------------------------------



  • 42.  RE: Dispelling the 'Myth' of the Missing Fundamental

    Posted 01-24-2024 23:07
    Steven Rosenthal,

    A linear system is one that obeys the laws of superposition. If you had a 200 Hz signal and a 300 Hz signal and you add them together (sum), they are independent and co-exisit with no output other than both of them simultaneously existing. We call that ‘orthogonally’.

    In a nonlinear system, there is some sort of multiplication going on between the signals, not just addition. If you multiply each one independently (a gain) you still have obeyed the law of superposition. If you multiply them together as in a mixer or modulator in a radio communication system, you have a nonlinear system.

    Imagine that you have now some unison strings coupled at the bridge. If the bridge does not completely isolate the unisons, they bridge is essentially coupling them in a nonlinear manner. This is a classic example of what happens in piano. The strings modulate against each other and you get a sum and difference from that modulation.

    You can ‘google’ the term nonlinearity or ‘nonlinear system’ and also watch some interesting YouTube lectures on this.

    Hope this helps. My point on the subharmonics was that we can psycho-acoustically perceive a 100 Hz note from a pure superposition of 200 Hz and 300 Hz but if we do a spectral analysis, we may not actually get a 100 Hz signal in the spectrum. Technically the spectral component has to exist for us to say that it is there in reality. If there is a nonlinearity between the two independent frequencies then we can get a sum and difference resulting in actual spectral components at 100 Hz and 500 Hz.

    Best,
    Steve