Self correction of AccuTuner questions

[Jim Coleman, Sr.]

Hi Kent:

In your answer to Doug H. you are correct in your statement about the
4:2 octave staying the same from C4 to C5. However, in my articles on
Altering the Stretch Numbers in the April and May issues of the Journal
in 1997, I went to great lengths to show from the math that it is necessary
to add-in, beginning at note C5, the amount of reset which is approx. equal
to the amount you have added to the A4 Stretch Number. This is necessary
for maintaining a smooth progression from B4 to C5. This also makes the
octave C4-C5 to be widened by that same amount on a SAT I or SAT II.

The new SAT III has a slightly different scaling formula which does make
the C4-C5 octave slightly wider. If one prefers a tighter octave, one can
invoke a negative Double Octave Beat Control. If one prefers a wider yet
octave C4-C5, one can utilize the new Double Octave Beat Control to increase
the octave width by using a positive DOB. This can be done on the fly
without recalculating the basic FAC Tuning. This is my preferred manner.
However, if one wishes to just automatically widen every tuning like this,
one can set the DOB first and have it figured into the Tuning Record by
doing the STRETCH - MEM after the DOB is set.

Since FAC tunings are predicated upon the idea of controlling the double
octave throughout the piano, the DOB can be used to expand OR contract
the double octave relationships. Naturally, this will also affect the
intermediate single octaves. If one wishes to have more control on the
single octaves, it can be done by altering the DOB along the way. More
on this later.

One can also utilize the altering of Stretch numbers in addition to using
the DOB, so there are many many ways to alter an FAC Tuning. My personal
preference is to use the DOB with plus figures in the treble and minus
figures in the Bass for most pianos except 7' or 9' grands where the FAC
works just fine.

As was pointed out in the above mentioned articles, altering the C6 Stretch
Number affected the top octave primarily. A 1 cent alteration will make
approx. a 5 cent affect at C8. In a similar fashion, altering the F3
Stretch number primarily affects the Bass. One can use combinations of
altering the 3 stretch numbers in parallel or contrary manners to do some
radical changes to the standard FAC tunings. Imagination is probably the
only limitation, but using the DOB is so much easier.

Another area where the DOB facility works quite well is in the area of
uneven scale breaks. I will be writing an article on handling the typical
Acrosonic break area using DOB (Double Octave Beat) control. This should
come out in about two weeks on the email list and perhaps a couple months
later in the Journal. I plan to demo this in KC next week.

Jim Coleman, Sr.

On Thu, 15 Jul 1999, Kent Swafford wrote:

> Doug  Hershberger wrote:
> 
> >In the
> >area of the piano we generally use 4:2 octaves such as the mid range, I
> >sometimes  will tune the octaves aurally and then check to see what the
> >accu-tuner says about it using a FAC tuning on a page of memory. I am
> >talking about a well scaled piano and a FAC that fits pretty well. What
> >seems to be the case with me is that no matter how conservatively I try to
> >make the octave stretch the accu-tuner still says the octave is sharp
> 
> This is a standard feature of FAC tunings, as calculated by the SAT I, 
> SAT II, and the SAT Librarian computer program. I don't have specific 
> knowledge of the SAT III.
> 
> In FAC tunings the notes of octave 4 are tuned at the 4th partial.
> In FAC tunings the notes of octave 5 are tuned at the 2nd partial.
> This means that FAC tunes "direct interval" 4:2 octaves between octave 4 
> and octave 5.
> Check it out. In an FAC tuning, the C4-C5 will generally be tuned as a 
> pure 4:2 octave.
> This means that the C4 value at the 4th partial (C6) will be the same as 
> the C5 value at the 2nd partial (also C6). However, above C4-C5 the 4:2 
> octaves become narrow in almost _all_ FAC tunings. The reading for each 
> note in octave 5 will be lower than the same note in octave 4, and both 
> are being read at the level of the 4:2 coincident partials.  This 
> explains your observations completely.
> 
> Try it and compare the readings between corresponding notes in octaves 4 
> and 5. Raising the A value will not help; a higher A value will _not_ 
> keep the 4:2 octave4-to-octave5 octaves from being contracted in FAC 
> tunings.
> 
> Raising the C value will widen the octave 4 to octave 5 4:2 octaves, but 
> may affect the the rest of the treble too much to be of much value.
> 
> Kent Swafford
>