Unison beats good?

[Billbrpt@AOL.COM]

In a message dated 11/6/98 12:50:32 AM Central Standard Time,
pianotoo@imap2.asu.edu writes:

<< > List,
 > "Even the unison strings of a piano sound better when de-tuned to a minute
 > degree (app. 2 cents total spread, corresponding to 2/3 beat per second @
 > a440). Fortunately a good piano tuner attempting to achieve true unison
gets,
 > on the average, a similar result"
 > 
 > Dr Daniel W. Martin
 > H D Baldwin Co
 > Tech Jo. April 1964 >>

The figure above is twice outside the tolerance on the PTG RPT Tuning exam.  I
think most contemporary tuners would consider those to be poor unisons.
Someone else mentioned a possible error in figures.  Could the author have
meant .2¢ (not 2¢)?  If so, the variation from exactly on would be in line
with what I have seen come from the best tuners who have taken the Exam and
whose unisons have been measured in that clinical setting.

There was a story in Scientific American about 20 years ago called "The
Coupled Motion of Strings".  Not having the text for reference, I remember
that it concluded more or less that the best tuners produce this kind of
error.  My personal opinion is that the tuner strives for a perfect unison
which means "no beat".  If there is a 1/2 beat per second or less, the tuner
may be satisfied with it because the beat is simply inaudible. 

 I think it can matter depending on the circumstances.  In a usual, in-home
tuning that I do on a piano say, once a year, I won't listen to a unison long
enough to even know if there is that slow of a beat.  During a concert tuning
however, I may pound away at a unison for a considerable time, just to make
*sure* there is no hint of a beat.

>From what I have learned, the unison is really the only interval where it is
even possible to have absolute perfection and that is the goal.  5ths and
octaves can *sound* pure and thus be perceived as beatless but we know from
the understanding that has come about in recent years that inharmonicity
prevents coincident partials from ever lining up perfectly.  Therefore, there
is always some kind of beat in these intervals whether it is perceptible or
not.

When tuning the 5th and the octave, the tuner may choose to favor one set of
coincident partials over the other or may make a compromise between them in
order to create a desired effect, expanded or contracted, as desired.  With
the unison however, I believe the consensus has it that it is to be absolutely
pure or as close to that as possible.  The very small variances that have been
noted in the unisons of the best tuners are a result, I believe, of the
physical limitations of both the piano and the tuner him/herself.  An error of
.1 or .2¢ is *readable* by an ETD but probably inaudible to the ear.

Furthermore, there is always the dilemma of the False Beat.  Practically no
piano is completely without them.  It is possible that some very skillful and
artful tuners can in effect, cancel out a false beat by countering it with a
deliberate but slight beat in the unison.  In such a case, the three strings
would most surely have as much as (or perhaps even a little more than) a full
cent difference between them.

Sincerely,

Bill Bremmer RPT
Madison, Wisconsin