[CAUT] Unison Tuning

[Ed Sutton]

I would like to remind the list of Jim Ellis's articles "Unisons- the
Effect of Tuning on Persistence and Timbre," in the Sept., Oct. and Nov.
1982 _P. T. Journal_.
These articles should be reprinted in the _Journal_, maybe with some study
questions added by Mr. Ellis.
Ed Sutton


> [Original Message]
> From: James Ellis <claviers@nxs.net>
> To: <caut@ptg.org>
> Date: 3/4/2005 10:30:09 AM
> Subject: [CAUT] Unison Tuning
>
> Ladies, Gentlemen:
>
> This is a continuation of a subject under a different title "Sacrifice
(was
> tuners-technology)".  I'm using a new title that addresses the current
> discussion a little better, i.e., the unision going slightly falt when all
> three strings are tuned.  Several things are happening here, and they are
> getting glossed over as generalities, which they are not.
>
> Virgil Smith is correct about some things, incorrect about others.  Jim
> Coleman is correct within the bounds of his statements.  But there is more
> to it than that.
>
> Fred Sturm is right on target here.  Measuring single strings (in a piano)
> to an accuracy of 0.1 cent is puching the limit, if it isn't already past
> it, and that's not the fault of the ETD.  It's just a limitation of pure
> statistics - the data available to the ETD - limited by the decay rate of
> the various paritals and the stability of the string's vibration.
>
> All other things being equal, I would expect the fundamental of the note
to
> go a tiny, tiny, tiny but flat during the "prompt sound" when all three
> strings are tuned due to the mutual coupling at the bridge.  But after
> that, I would expect it to turn around and go the other way during the
> "after-sound" due to the fact that the three strings, sooner or later,
WILL
> go out of phase, no matter how accurately the unison is tuned.  It's a
> basic law of physics.  I'm saying the pitch produced by in-phase strings
> will be ever-so-slightly lower than that produced by out-of-phase strings
> due to the mutual coupling, and that will depend upon how much mutual
> coupling there is, and how fast the decay is.
>
> Another thing no one so far has mentioned is the fact that the bridge
> itself is NOT rock solid.  When pressure is applied to a bridge pin, it
> DOES move - by a microscopic amount - but it moves - and the movement of
> one pin will move the next one a little bit.  Wood grain is springy.  I'll
> bet that if you very carefully measure (on the same note of the same
piano)
> unison tuning going from sharp to flat, you will find this effect is not
> the same as when you tune going from flat to sharp.  I have not done this
> experiment, but that is what I would expect to see if I did.  Again, as
> Fred points out, we are making measurements that are on the fringe area of
> the resolution we can obtain in a real piano, and we are bound to get
> scatter in the results.
>
> One more thing that Fred also mentioned:  If all three strings of a unison
> are within about 0.5 cent of each other, the fundamental will lock in due
> to mutual coupling, and it won't beat, but some of the higher partials
> will.  As you get the unison more closely tuned, the higher partials will
> begin to lock in, and not beat.  I have done those experiments, and they
> prove to be true.  When you aurally fine-tune unisons, you are actually
> listening to the higher-pitched partials, as the fundamentals have long
> since stopped beating.
>
> We are looking at something here that is very complex, and we cannot
> account for it with one single, simple, explanation - but it CAN be
explained.
>
> Sincerely,  Jim Ellis 
>
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