There are 3 partial changes in an FAC tuning. From the top down here are their locations:
The Treble Partial Change: B5/C6
The Middle Partial Change: B4/C5
The Tenor Partial Change: B2/C3
Here are the new and improved locations for each of those partial changes:
The Treble Partial Change should be lowered to G#5/A5
The Middle Partial Change should be lowered to A4/A#4
The Tenor Partial Change should be lowered to G#2/A2
The treble partial change is lowered so that A5 uses the fundamental (1st Partial) instead of the 2nd Partial. Using the fundamental @ A5 makes tweaking the treble stretch easier. Using the fundamental @ A5 allows us to see exactly the width of the A3/A5 double octave, and makes it easier to use the D4/A5 12th for stretching the treble. Since A6 is using the fundamental, it is easier to tweak the treble using D4 as the reference note and see and hear the widths of the D4/A5 12th, and the D4/A6 19th when determining a new stretch for the newly tweaked FAC tuning.
The default partial used in an FAC for notes C5 – B5 is the 2nd partial. If the treble partial change is left as it is, A5 is using it’s 2nd partial for the tuning and a conversion is necessary to tweak the treble accurately and easily for a good sounding location for both A5 and A6. Without lowering the partial change so that A5 is using it’s fundamental rather than it’s 2nd Partial, the conversion that’s necessary is too complicated and takes too much time and effort – especially compared to simply lowering the partial change from B5/C6 down to G#5/A5. That takes care of it. Using the fundamental for A5 makes tweaking the treble much faster, easier, and more accurate.
The Middle partial change is probably the least important of the 3. The only reason I’ve heard for lowering this one is to remove any ‘tail’ that can be created within the FAC tuning’s calculation. Some tuners have commented they found Bb and B ended up being too sharp. After lowering this partial change and the treble partial change, the 2nd Partials will be used form A#4 – G#5. Again, this partial change is the most optional of the three, but if you’re doing the other two, why not do this one? All three will need to be corrected anyway. Once you learn how to do these each one will only take a few seconds.
The Tenor Partial Change. is the most important one to lower. And if you only do one, lower the tenor partial change.
Lowering the Tenor Partial change down to G#2/A2 puts that partial change onto the bass bridge in most pianos – all except the long scales. On most verticals and virtually all the grands under 6′ the FAC partial change of B2/C3 ends up at the low end of the long bridge. This area of the piano is fraught with issues. If we can get the partial change out of this area, we are doing our tunings a favor. The transition from plain wire to wound bichords, as well as the transition from the long bridge to the bass bridge. Having a partial change in there, just adds to the issues.
Lowering the tenor partial change down to G#2/A2, getting it off the long bridge and down onto the bass bridge is not only a good thing for the tuning, it’s really easy to do. It only takes seconds.
So why not just just get into the habit of lowering them all? Once they are all relocated, the next tweak is to correct any potential errors there are with each one. The AccuTuner has a feature to help do this. We call it the Partial Change Correction feature, (PCC for short). PCC takes care of the math and makes the correction by pressing only 2 buttons. It’s easy and fast.
Once the partial changes have been lowered AND corrected, the tunings will sound better because any potential errors at those partial changes have been eliminated. Being able to tend to these partial changes is unique to the Sanderson AccuTuner. None of the other tuning software programs can do this. And too, the AccuTuner only has 3 partial changes whereas most of the other software ETDs, will have 5 partial changes in their tunings!! They actually have more of a need to correct their partial changes, but with those other systems, there’s just no way to do it. The AccuTuner only has 3 partial changes and they are easy to fix!
Once all the partial changes have been relocated and corrected, tweaking the treble stretch can really set your tunings apart from anyone and everyone who’s NOT doing these tweaks!