Unison coupling

[Ron Nossaman]

>In your comment below about the pitch rise which you noted as dropping
>in about a half second I believe is just the normal pitch drop which
>we have been talking about for some time.

* Hi Jim. Maybe, maybe not. That pitch drop of one string after the first
half second is no problem. It has a good clear reasonable explanation. The
progressively FASTER pitch drop, through approximately the same Hz ranges,
after the second and third string are tuned in is one of the things that
I'm curious about. That one hadn't been discussed at all as far as I know
until I mentioned it, and Kent confirmed that he had noticed the same
thing. So far, still, no one else seems to have tried this, or they have
and aren't talking. What has been widely reported, measured, discussed, and
demonstrated to be verifiable without instrumentation is the apparent
(aurally, with interval checks) pitch drop through the dwell (long term)
phase. That's the portion of the envelope where all the tuning checks are
done, and that was what I was originally hoping to tie in with soundboard
assembly impedance when I first (rashly) mentioned it. Though it's all
almost certainly related, this changing rate of pitch drop in the first
half second is something entirely different that I stumbled across in my
first attempt at taking pitch measurements, and I can't seem to get that
point across. The precise timing of the long term pitch drop shouldn't be
that critical, since it's relatively stable for a fairly long period. On
the long term pitch drop seen when adding the second/third string, the
amount of pitch change was what everyone was concerned about and has been
discussing. On the short term pitch drop, the change in the TIMING of the
drop with the addition of the second and third string was of more interest
to me than the amount of pitch change. That short term drop happens too
quickly for me to get any dependable accuracy of pitch measurement anyway,
but the change in the rate of drop is quite dramatic and obvious.    


>If you have occasion to borrow a SAT, you can play a note repeatedly
>(perhaps 4 blows per second) then you can isolate the prompt pitch
>and actually measure it. 

* That's the plan, when I get some time to chase it around a little. If I
can get pitch readings at peak attack, and mid dwell with one, two, and
three strings, and some idea of the timing of the peak pitch drop with one,
two, and three strings, perhaps I can get some correlations. 



>Back in the 60s when I did a lot of measuring of inharmonicity of piano
>strings, I decided that plucking the strings would give the most
>consistent results because when striking the string the pitch was changing
>too rapidly to get consistent results due to the moment in time that the
>measurement was taken. 

* This is interesting. Has anyone measured a pitch drop from one, to two,
to three strings by plucking instead of hammering? It seems like a
reasonable way to separate the peak pitch from this test too.


> Then, when it comes to trying to tune within .01 cents,
>as I pointed out in a Journal article about a year ago, this is ridiculous.

* Yea, well, I was only looking for generally predictable trends rather
than "truth" to twelve decimal places, so that one doesn't disturb me much.

Thanks Jim, maybe what I think I'm looking at makes more sense to a few
more folks now. I appreciate it. 
Ron N