[CAUT] Unison Tuning

[Horace Greeley]

Jim,

...couldn't agree more...very well said.

Thank you very much.

Best.

Horace


At 07:47 AM 3/4/2005, you wrote:
>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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