was Accu-Tuner now tuning question

[Kent Swafford]

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