ETD accuracy measuring partials

[Richard Moody]

I am sure ETDs measure the fundamental with great accuracy.   This was
covered in Robert Scott's article in Aug PTJ. "Calibration of Pitch
References".

The question I am raising is how accurate are ETDs when measuring partials?

When ETD show a variance of partials on the same instrument I would like to
see if that ETD is tested for accuracy of measurement of those partials.
One test might involve two ETD's.  If both give the same readings, and show
the same variance, yes it can then be assumed the partials are changing.

The reason I question that partials are changing is that it is hard to
logically explain how the partials can change when the fundamental doesn't.
Partials are the vibrating segments of steel wire.  The only way they can
change is for the frequency to change.  Cents is only a measure of
difference between two frequencies.  The partial freq is measured against
the theoritical harmonic frequency.   The difference between these two is
expressed as cents.  It seems reasonable that a steel wire should be
expected to produce the same partials to the same fundamental.   The only
way I can visualize a partial changing frequency is for the length of the
segment to change.  The only way I can see this is for the nodes to get
wider or narrower.

But before all this speculation I would like to see it demonstrated that 2
different machines show the same variance a first machine shows.  With the
wide spread availability of ETD's this should be easy to accomplish.

I know it has been stated and results posted to this list that hammer blow
force influences partials.   As far as I know that was done with one
machine and a weighted key striker.     It could easily done with two or
better 3 machines.  I think this is important because in the original
publications of experients for inharmonicity  Young and others stated that
hammer blow and thus string amplitude had no effect on inharmonicity or
effect that they could measure.  These were reprinted in the Journal in the
50's.   It was from those experiments the inharmonicity formulas used today
were developed.        ---ric