String coupling.

[Kent Swafford]

on 6/20/00 7:25 PM, Ron Nossaman at RNossaman@KSCABLE.com wrote:

> tuning each
> string of a unison as perfectly as I was able to the Tunelab display, the
> unison did indeed drop when all were sounded together, just like you said.
> Also in every case, the unison sounded rougher than I can tune it aurally.
> Touching up aurally, the unison pitch drop disappeared again, or was
> greatly reduced. Checking each string individually against the display,
> they weren't precisely the same anymore, but the unison as a whole was on
> pitch and sounded good.
> 
> Why?
> 
> Right or wrong, I think it's because there's no reason to assume that the
> partial structure of all three strings in a unison is identical, and they
> in fact aren't.

So this variable is a mismatch in inharmonicity, just as we experience every
day in wound bass strings.

This is but one variable with which we are dealing. There is every reason to
think that there are also other variables at work.

Another variable is the pitch envelope of a sounding note. Piano strings do
not necessarily vibrate at a stable pitch, but rather can vibrate at a
continuously changing frequency. We know this because out VTD's exceed the
stability of vibrating piano strings and can display the changing pitch
while a note is sounding; this is the cause of the VTD's display changing
speed and/or direction while a string is sounding. Two strings which have
similar pitch envelopes can be tuned together no matter how unstable;
strings that have different pitch envelopes cannot really be tuned together.

Another variable which is rarely discussed is the behavior of a VTD display
in the presence of more than one frequency. Does the VTD display the lower
pitch, the higher pitch, the average pitch, the loudest pitch, or a random
combination of all the above? This is an important question to ask, isn't
it? Do we know the answer? I don't think we do.

In order to answer the questions about string coupling, we need to know a
bit more about how VTD's work, in my opinion. If we are going to claim that
3 strings vibrating together do so at a frequency different from the same 3
strings vibrating individually, we must learn about how blended frequencies
are displayed on a VTD. We concentrate on the fact that readings seem to
change, but do we know enough about VTD behavior to know that the
frequencies actually change, or does the inevitable mix of frequencies just
display differently?

Kent Swafford

PS -- In RCT-speak, "full-blush" is not accurate enough when tuning unisons.
When we are dealing with pitch envelopes, in order for a unison to be clean,
and assuming that the envelopes of the 3 strings are similar, the full-blush
must happen at the same time/place in each of the 3 envelopes.

KES