SAT Part 1 Altering the Stretch numbers

[Jim]

Dear list:

Here is the first of a series of 5 or 6 from Jim Coleman, Sr.



SAT Part 1 - Varying the Stretch

Since so many people on the list are using the Sanderson AccuTuner,
I tho't it would be well to describe the principles relating to the
normal stretch tunings.

When one uses the FAC measurements carefully, the particular piano
will be tuned such that the double octaves will be rather
consistent thoughout the entire piano.  The actual scaling of a
piano may have some strange quircks, especially in the area of the
breaks between bass and treble wire and sometimes across plate
struts.  One can depart from the smooth programming of the SAT to
smooth out these breaks a bit.

In the Tenor section where there is some fore-shortening of the
plain steel wire due to case size limitations, one can gradually
from A#3 down subtract .1 cent per note till the lowest plain string
is reached.  This amount should be progressive and as a deviation
from the normally programmed cents readings.  You can see a specific
example later below.  You can visually discern this fore-shortening
by the hockey stick shape of the tenor bridge or the slight reverse
curvature of the V-bar or Agraffe line.  In the case of an Acrosonic
spinet, you might want to subtract .2 cents. ie an additional -.2
for A3, then an additional -.4 for G#3, and an additional -.6 for
G3.  Since these notes have shorter and thicker strings, their
inharmonicity is greater than normal.  Conversely, the highest wound
strings need to be raised because their inharmonicity is much lower
than usual.  You might try adding say .4 cents to F#3 and also a plus
..4 cent addition for F3, and plus .3 cents addition for E3 & D#3 and
a plus .2 cent addition to D3, and a plus .2 cents addition for C#3.
This will smooth out the beat rates of the major 3rds at the slight
expense of the minor 3rds, but the octaves, 4ths and 5ths will be
more even.  This same principle will work with the new RCT.  Some
pianos such as the Yamaha verticals will need very little of this
type correction.

The main purpose of this series of articles will be to show how to
vary the octave stretch, but before we do, there is one more thing
that needs to be addressed.  This is a method to insure that the
fundamental of A4 will be exactly on A-440.

With the advent of the FAC stretch tuning in the SAT, all notes from
C3 thru B4 are tuned by their 4ths partials.  Due to the necessity of
smooth curve fitting of the 3 measured notes (F3, A4 and C6), the
fundamental of A4 may not always be exactly at A440.  In most cases,
this can be ignored; however, for tuning testing purposes and some
critical recording purposes, you may need to know that the A4 is
right on.

After the 3 measured notes have programmed a tuning on a page of
memory, you can advance to A4 and carefully tune it to stop the LED
rotation.  Then press the Tune button once and the down octave button
twice to get to the fundamental of A4.  Play A4 and if the LED's are
rotating in the sharp direction, touch the up cents button a few times
until the rotation stops. Write this cents number down.  This number
represents how sharp the piano will be tuned if you do nothing about
it.  To correct this, use the down cents button till the same number
is on the minus side of 0.0.  Then use the combination buttons like
this to reset the pitch: hold down the SHIFT button, hold down the
MSR button, release the MSR button, release the shift button.  Now
after pressing the MEM button, you can begin tuning from anywhere and
be assured that the A4 will be right on.  Everything above it will be
progressively sharp, and everything below it will be digressively
flat, but it will fit together well.

Next article will deal with altering the A4 stretch number in order to
stretch the tuning higher in the Treble and flatter in the Bass
because there is a tendency of some technicians to prefer a wider
spread in order to provide better homogeneity through out the piano.

Jim Coleman, Sr.