Adjusting the treble stretch in an FAC tuning

An FAC tuning uses double octave stretch for tuning the treble.   That means for tuning A6, A4 is being used as the reference note to ‘find’ the location for A6.  However if more stretch is desired, other reference notes can be used.  For instance, if more stretch is desired, different reference notes can be used to locate A4.  The reference notes must have been tuned, but once tuned to the FAC tuning, D4, A3 and D3 can all be used to add stretch to the treble tuning.  The farther away the reference note is from the note being tuned, the more the stretch.   For instance, using D4 as a reference note for tuning A6, will be tuning A6 as a double Octave + 5th from D4.   Using A3 as a reference note will be tuning A6 as a triple octave from A3.
For starters, I’d recommend using D4 as the reference note for finding a new location for A6, and use that DOB setting for all notes above A4.   Once D4 has been tuned to the FAC tuning, on the FAC tuning, step up to A6.  Play D4 and observe the lights rotation,  the lights rotation should indicate that the FAC setting for A6 is flat.   Now add enough DOB to stop the lights on A6 when playing D4.   That’s really all there is to it.  Use this amount of DOB for tuning the treble (above A4).  (Make sure to remove the DOB when tuning below A4).

For some aural checking. . . . .

Use as many aural checks as you want to check the new treble stretch.  Do enough aural checking to make sure the treble is nicely stretched.  Generally speaking, a few good aural checks should be enough. The notes used for the aural checks will need to be tuned using the FAC tuning.

Some notes to tune to be used for checking A6 are D4, A4, D5, A5, and D6.   Pay particular attention to the D6/A6 5th.   It should sound pretty nice.  Don’t be afraid to add a little more DOB- maybe in .1 increments until a nice stretch is found for all the reference notes being used.

It is not at all uncommon to want raise A6 above the initial double octave +5th setting!  Most of the time that pure double octave+5th (D4/A6) is really close, but other times more stretch might sound even better.  Again, let your ear be your guide.  The pure double octave+5 is very ‘safe’, so if the idea of stretching more than what the default FAC tuning contains, sticking with the pure double +5 will be a good place to start.   But after more listening and more experimentation, don’t be afraid to add some more DOB.

Some might want to use an average of the Double octave + 5th with the triple octave (which uses A3 as the reference note).   Simply alternate playing A3 and D4 and find a location for A6 where one will rotate the lights one way and the other the other way.  Just find the compromise and use that DOB setting to tune the treble.    Using D3 (and sometimes even A3) to locate A6 is only recommended for the longer scales.   On the shorter scales D3 is often a ‘bad’ note to use for this.   But on a nice long scale using D3 can be used as a reference note for treble stretching.   It can be used in combination with D4 for finding higher locations for A5, A6 and A7.

(The amount of DOB available varies in different AccuTuner models.  The range of DOB in the SAT I, SAT II and SAT iII is +/- 2.0.   But the DOB range in the SAT IV “980” has been expanded to +/- 10.0!   When using D4 and/or D3 for tweaking the stretch of an FAC tuning, 2.0 DOB will probably not be enough.   After all, the default treble stretch of an FAC tuning is double octaves.  I.e. A7 is tuned as a double octave from A5.  Most of the time, on most pianos, there’ isn’t enough DOB in the standard SAT models to end up with an FAC tuning, tuning a triple octave @ A7.  There’s just not enough DOB to change those doubles into triples.   But a SAT IV “980” has plenty of DOB for this!!)

When using D3 to help find a good location for A6, it is very important to be thoughtful about how ‘good’ a reference note D3 might be.   It may be a very under tensioned plainware trichord, or maybe a wound bichord, and so on.   When designing a scale for the shorter pianos, there are many compromises that need to be made in that tenor area.   So just take that into consideration when using D3 as a reference note to find A6.   D3’s ‘quality’ as a reference note increases on the longer scales.  The longer the scale the farther out of that scaling ‘danger’ zone D3 will be.

With some experience, it will become obvious if D3 is useable or not and how much help it can be for finding a new setting for A6.

Of course, both D3 and D4 will need to be tuned to the FAC tuning before using them as reference notes.  With the SAT set on A6, after tuning both D3 and D4 to the FAC tuning, alternately play D3 and D4 and observe the lights rotation.     Another method is to stop the lights at each and make note of each setting, and then set the SAT to be right in the middle of the two.

Once the sweet spot for A6 is found using both D3 and D4, set the DOB to give you the setting you want @ A6, and then tune the other notes desired for aural checking (D5, E5, A5, D6, E6, and A6).  Pay most attention to the 5ths but keep an ear on the octaves as well.  There may be one particular interval in the aural checks that indicates more or less DOB should be used.  It’s easy to add or subtract DOB and find the stretch you like up there.  A little experience with this will make it easier to find a good sounding treble stretch for the piano.

Sometimes our “tuner’s” ears – especially if this is new to them – will guide us to a more familiar and ‘lesser’ stretch.   But to really ‘hear’ what this new treble stretch sounds like we need to put on our ‘musical ears’.   This needs to be done on a number of different pianos.  Complete tunings on a number of different pianos.  I’ve often felt like I was stretching too much during the ‘mapping’, but then when the piano was finished, I thought I could have gone a little higher.   But this is a personal decision and each of us need to find what that is for us.

Just remember to use this DOB setting for the treble ONLY!!  –  from notes A4 – C8!!

Different model SAT’s have different DOB ‘ranges’.

The DOB ‘range’ is the amount of DOB that can be added or subtracted from the tuning.  The first DOB range was +/- 2.0.   This is the DOB range for SAT models I, II, & III.
The Standard Model SAT IV originally had a DOB range of +/- 2.0 and probably still does.   If you have a Standard Model SAT IV, you can find out what the DOB range is by simply holding down the BluShift + CentsUP buttons.  It will probably go up to 2.0 and then stop.

The SAT IV “980” originally also had the same +/- 2.0 DOB range.  Some new firmware updates have expanded that DOB range to +/- 4.0 or a +/- 10.0 firmware update – depending on the update.

Expanding the DOB range makes it possible to stretch the FAC’s treble to whatever the technician might want to do.  Since the default stretch of an FAC tuning is basically double octaves, if the technician wanted to tune a triple octave @ A7, the original +/-2.0 range just wasn’t enough.   But with the +/-4.0 range, the FAC’s treble tuning can be tweaked to give a triple octave @ A7.
For even more stretch, like tuning a triple octave +5th @ A7, and even higher, the DOB range has been extended to +/-10.0.  This expanded DOB is available thru a Firmware Update that can be done by the user.   To check on a firmware update for your particular SAT IV, just give Inventronics a call.  Once you have the update file, it can be installed into your SAT using your PC.


Using more than one DOB setting for treble stretching.  One for A6 and another for A7.

Once the above method has been used for finding a good location for A6, if desired, DOB can also be used to get even more stretch out in the highest octave (A6 – C8).

The first step is to find out what a good setting for A7 might be.   There are a couple good choices for A7.   For tuning a triple octave, use A4 as the reference note (with SAT set to A7, play A4).   Another choice is to use the same D4 reference note used for A6.   If D4 is used, A7 will be tuned as a triple octave + 5th.   (If D3 is used, A7 will be tuned as a quadruple octave +5!!!)   I’d suggest starting with D4 as the reference note.

Doing this will involve more DOB button pressing and listening than using just one DOB setting for the complete treble.

Just set the SAT to A7 and play D4 and A4 alternatively.  Using A4 will put A7 at the triple octave and D4 will put A7 at the triple octave +5th.   Of course, the A7 setting can be compromised by having one reference note rotating the lights one way, with the other rotating the lights the other way.  Generally speaking, favoring the higher pitch is better.

Once the new setting for A7 has been selected, write it down.

Now all that is needed is to see how much DOB is needed to put A7 at that new setting.

With a range of only +/- 2.0 DOB, there won’t be enough DOB to get A7 that high.   This is why the DOB range has been expanded.   There’s not enough DOB to make a triple octave out of the double octave that is the FAC default.

For those who have the SAT IV or the SAT IV “980” with updated firmware containing the extended range DOB, there is enough DOB to do this.   All the more reason to upgrade to a new SAT IV “980”.

Each .1 DOB affects A7 by .6 c.   So to raise A7 by 2.0 c.  .3 DOB will raise it by 1.8 c.   .6 DOB will raise it by 3.6 c.  .8 DOB will raise A7 by 4.87 c. and so on.   Just figure out how much more DOB is needed to put A7 at it’s new location.

Now there are 2 places in the t reble that need a specific DOB setting.   The A6 DOB setting can be put into the SAT @ A4 and will be used to tune notes A4-A6.   The additional DOB should be incrementally added as the notes above A6 are tuned.   Depending on how much more DOB is needed in the high treble, maybe .1 can be added on each note.   Maybe .1 should be added on every other note.  Maybe add .1 to the first three notes, and then .2 to each of the next 4 notes and then maybe .3 to the each of the  next 5 notes.  Incrementally add DOB so that when A7 is tuned the correct amount of DOB is being used.  Use that DOB for the top 3 or 4 notes (A7 – C8).