[CAUT] Unison Tuning

[Fred Sturm]

On 3/4/05 7:33 PM, "Don" <pianotuna@yahoo.com> wrote:

> Hi Fred,
> 
> I picked the Baldwin because the three wires were clean sounding--and it is
> piano that is very stable, and has been so for several years. It also
> happened to be one that I was working on.
> 
> I did not take measurements of the outside strings. There were no audible
> beats when I ghosted at the 2,3,4,5 and 6th partials on the three string
> unison, nor on the single string when I did the same. Nor could I hear any
> when I simply played the note. I don't quite trust ghosting to show falseness.

    The thing is, a unison can sound utterly perfect to the ear, and easily
measure 0.2 to 0.3 cent variance between strings. If you don't measure each
string, you won't know if the two outer strings happened both to be 0.2
cents flat of the middle one, for instance: equal to the unison on average.
    This morning I tuned a Steinway A for a concert. Nice piano which I
recently restrung, solid in pitch, clean sounding strings throughout, easy
to rend pins and strings. So I did a bit more experimentation. I read 7
unisons, scattered from B2 to mid octave 6. Same procedure as before: three
successive reading of each string within 0.1 cents of one another, and the
average pitch of each string within 0.1 cents of the other two. I just use
RCT in tune mode, using the measure button on the right (which fills in a
result in the offset window). Click the measure button and immediately
thereafter play the note. And then play again (careful to use the same
force) and look at the display to make sure it is "dead on" (full blush,
stopped cold).
    My results were interesting. For two of the unisons, the unison was
consistently 0.2 to 0.3 cents flat of the average pitch of the individual
strings. For one unison, the unison was consistently about 0.15 cents sharp.
The rest were too close to the individual string measurements to call one
way or another. What struck me was the consistency of the readings of the
two notes that did show the unison to be measurably flat. I repeated the
procedure a couple times to be sure, and kept getting the same consistent
readings.
    Again, of some intellectual interest, but of no significance whatsoever
to the daily tuning of pianos, IMO. Of more interest and use might be a wide
sample of testing of unisons where the individual strings were measurably
different from one another, say 0.5 cents spread. And then measuring the
unison to see what resolution the machine found.
Regards,
Fred Sturm
University of New Mexico