Mensurix

[Bernhard Stopper]

> If there is some new integrated approach to modelling these factors and 
> obtaining realistic predictions of string behaviour these results would be 
> important, so why not publish them and make them available for discussion, 
> instead of concealing them in a sea of commercial-eze? If the software is 
> actually based on Stulov+Hall then why not say that as these models are 
> well known already?
>

Stephen,

It is not a Hall model, and it is not a Stulov hammer.
The model is derived by higher order differentials, solved with usual 
difference schemes. All what is necessary to build such a model can be found 
in Klaus Jürgen Bathe´s book "Finite Element Methods".
Hysteresis is not a phenomene discovered by Stulov, it is relatively common 
used in finite element models.

For example, besides hysteresis, the Mensurix hammer also considers felt 
friction on the surface caused by the bearing length (causing a movement 
along the string due to the rotation around the hammer axis) and the 
difference in friction caused by the wound strings.
Any jumps in string mass at the break, what can be found on good instruments 
(i.e. the wound strings are thicker than required by calculations with 
static spring/impedance models) are more plausible when simulating with 
Mensurix.

You are right, since it is a commercial program, i don´t publish exactly 
what i am doing, but i hope the information i gave here is at least more 
than nothing.
There is nothing really new in the used theory/models.

But have you ever seen Yamaha open their black boxes when using physical 
modeling in their synthesizers or Bill Gates giving the source code for his 
Windows Kernel?

best regards,

Bernhard Stopper

----- Original Message ----- 
From: "Stephen Birkett" <sbirkett@real.uwaterloo.ca>
To: <pianotech@ptg.org>
Sent: Saturday, April 16, 2005 5:54 AM
Subject: Mensurix


> With the recent resurgence of the P12 tuning threads, I re-visited some of 
> the old posts and came across some about the Mensurix software. This 
> reminded me of some concerns I had had at the time on the subject of 
> applied predictive models ....
>
> Predicting the behaviour of a real physical system with an applied model 
> is a huge can of worms. Any computer savvy person can write software that 
> "incorporates a physical model" and give it a fancy trademark name. For 
> instance, when Bernhard writes:
>>There is also the new Mensurix 5 on the market what is the only scale 
>>program available that uses a physical model of the string, to get more 
>>realistic sound relevant information for scaling.  (the physical model is 
>>build automatically from the string measures of the scale)
> this really doesn't say anything at all about the validity of the 
> predictions derived from that software.
>
> Commercial trumpet blowing is ok and necessary up to a point when trying 
> to sell something. And some level of product secrecy is especially 
> important for marketing software. With models, though, you can't afford to 
> put out a black box and expect people to take it on faith. Secrecy has to 
> be tempered by the damping [now there's some mixed piano metaphors] it 
> places on serious discussion of technical issues and serious evaluation. 
> Transparency is needed before a model can expect to achieve any sort of 
> reputation as a useful predictor of reality.
>
> Now I've never seen any reference to what physical model of the 
> string-hammer interaction is being used in this Mensurix software. Is this 
> information available somewhere? A perfectly respectable model could very 
> well be put together in a couple of hours using a simple nonlinear spring 
> and the old Suzuki modal transmission line for the string (I showed 
> exactly that sort of model at the PTG-Dearborn way back). It would seem 
> pretty sophisticated, especially packaged in a nice interface, and give 
> complicated looking predictions that wouldn't really be much use at all 
> for practical design. An improved model could be put together with a bit 
> more effort and the string bashed using  a Stulov felt hammer according to 
> a Donald Hall hammer string interaction. This one would look 
> super-sophisticated, especially with the Stulov hysteresis, but it 
> wouldn't inspire me with any more confidence as a practical design tool 
> than the simple nonlinear spring. Perhaps Bernhard has some new 
> unpublished model in the Mensurix software? But we need details or we're 
> in the dark.
>
> The other side of this is validation which is the only way for a model to 
> earn confidence. This is touched on a little by the spectral predictions 
> referenced in the Mensurix advertising - predicted vs real spectra - but 
> the lack of details makes it impossible to assess those claims. And 
> spectral predictions are notoriously imprecise as objective measurements 
> of what strings actually sound like (representing a  very wide 
> paintbrush.) This is not to say I don't believe the predicted vs real 
> spectra, just that it's impossible to make a judgement of the model with 
> the information provided. The acid test would be objective, preferably 
> independent, scientific testing of the model predictions in a variety of 
> areas, especially things like "strike point optimization" and "contact 
> ratio", which are somewhat intangible concepts incompatible with intuitive 
> evaluation. After all the software isn't cheap so some expectations should 
> be allowed.
>
>>The time, the hammer is in contact with the string is the main effect of 
>>how
>>many partials and in what weight they will occur.
>>...another important effect on the overtone weighting is the shape 
>>(curvature
>>and width) of the hammer surface.
>>...the contact time itself is affected by the hammer stiffness 
>>(complicated
>>parameters), the hammer mass, hammer damping loss and hammer shape and the
>>strings stiffness, tension and mass.
> If there is some new integrated approach to modelling these factors and 
> obtaining realistic predictions of string behaviour these results would be 
> important, so why not publish them and make them available for discussion, 
> instead of concealing them in a sea of commercial-eze? If the software is 
> actually based on Stulov+Hall then why not say that as these models are 
> well known already?
>


> Stephen
>
> -- 
> Dr Stephen Birkett, Associate Professor
> Department of Systems Design Engineering
> University of Waterloo, Waterloo ON Canada N2L 3G1
> Director, Waterloo Piano Systems Group
> Associate Member, Piano Technician's Guild
>
> E3 Room 3158
> tel: 519-888-4567 Ext. 3792
> fax: 519-746-4791
> PianoTech Lab Room E3-3160 Ext. 7115
> mailto: sbirkett[at]real.uwaterloo.ca
> http://real.uwaterloo.ca/~sbirkett
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