Robert Conrad, Registered Piano Tuner/Technician, Tucson, AZ

FAC Tuning Tweaks

The Tenor Partial Change Tweak


A partial change in a tuning is where the Sanderson Accu-Tuner (SAT) changes partials.   The SAT does this automatically with ‘FAC’ tunings.  You may not have even noticed the ‘jumps’ or ‘hiccups’ in the numbers, at those partial changes.

FAC tunings contain 3 partial changes.

(Click image to enlarge)

In the bass, the FAC tuning uses (listens to) the 6th partial on notes A0 – B2.   The use of the 4th partial begins on C3.    The other 2 partial changes in FAC tunings fall between B4 (4th partial) & C5 (2nd partial), and between B5 (2nd partial) & C6 (fundamental or 1st partial).  This article will only concern itself with the Tenor Partial Change – where the Sanderson Accu-Tuner goes from using the 4th partial (@ C3) to the 6th partial (@ B2).

Even though every partial change in every computerized tuning is important and needs to be checked, the Tenor Partial Change is probably the most important.     Making sure there is no error at the Tenor Partial Change will help the shorter scales sound better.  Once learned, you will probably check/correct the Tenor Partial Change transition on every piano you tune.    You may be somewhat surprised at the size of some of the errors you will be finding and fixing – with a simple offset and a little practice.    Incorporating this quick little tweak into your tuning routine will better fit the FAC tuning to the piano being tuned.

On many small and medium size grands, B2 is the lowest note on the long bridge.   Generally speaking, on those pianos, B2 is rarely a particularly ‘good’ note.    The inharmonicity of B2 can be quite varied.    B2 might be plain wire, or a wound bichord.    Making sure the partial change is correct is a good step in getting the tuning to sound better in this area, across the partial change, and down into the bass.

This article will address the FAC Tuning’s Tenor Partial Change that occurs between B2/C3, and will describe a method for checking the accuracy of this 6th partial to 4th partial transition, and correcting any error found there.

This can be done on any Sanderson Accu-Tuner that has FAC.   These instructions assume you already know:  1., how to measure FAC numbers,  2., how to store that FAC tuning on to a page in your SAT’s Memory, and 3., how to use the ‘Offset’ feature of your SAT (RST/MSR button).

Once you have the FAC tuning stored onto a page in memory, you are ready to check  the accuracy of the FAC Tuning’s Tenor Partial Change, and correct it if necessary.

In the MEM mode, look at the cents setting for C3.   Let’s say it is -3.2 c.  (C3 @ -3.2).   Now look at the cents setting for C#3.   Lets say the cents setting for C#3 is -2.8 c.  (C#3 @ – 2.8).    We now know the ‘difference’ in cents between C3 and C#3 is  -.4 c..    If we then tune B2,  .4 c. lower than C3, using the same partial as C3 (the 4th), we will have a good location for B2.

The 4th partial of B2 is B4.   To tune B2 using the above information, in the Tune mode, put B4 in the Note/Octave window and  -3.6 in the Cents window  (B4  @  -3.6),  and tune B2 on the piano to stop the lights.   (-3.6 c. is .4 c. lower than -3.2 c.)

Once the lights are stopped and B2 is tuned, go back to B2 on the FAC tuning in the SAT, play B2 and see if the lights are stopped.   If they are, the Tenor Partial Change has been computed correctly by the FAC tuning, and no adjustment is necessary.

But if the lights are not stopped a correction is needed.

For example, let’s say the FAC tuning setting for B2 is 2.0 (6th partial).   But after tuning B2 using the 4th partial  (.4 lower than C3, when you play B2), the lights are rotating.   Use the cents buttons to stop the rotation of the lights and observe the (correct) setting for B2.   Lets say when the light’s rotation is stopped the cents window now shows 3.3.    You need to make a correction of +1.3 c. (the difference of the FAC setting of 2.0 and  3.3) to have a smooth transition at the Tenor Partial Change.

Simply offset the SAT by 1.3 cents using the offset feature of the SAT.    Once the correct offset is stored into the SAT, with the SAT on the FAC tuning,  the lights should stop when playing B2.

In this example,  -3.6 (4th partial) = 3.3 (6th partial).    I.e., when B2 is correctly tuned to the 4th partial setting of -3.6,  the 6th partial setting should be 3.3.     The pitch is the same, the difference here is only in how that pitch is measured.    (These numbers are just for this example, of course, yours will vary).

This offset is used for tuning all the notes (in the bass) that use the 6th partial :  A0 – B2.   Don’t forget to remove this offset when you tune above B2!   If later on in the tuning you want to use the FAC tuning/SAT to check some notes in the bass – any note that uses the 6th partial (A0 – B2 inclusively) – you will need to use the Offset correction.

As of mid October 2015, the SAT IV operating system now includes a command feature that addresses the tenor partial change.  It is now possible to account for the partial change error without having to use an offset.

The settings for the 6th partial bass notes are corrected internally, within the SAT IV, so it is no longer necessary to have to remove or add the offset for tuning the bass, in order to have a clean smooth transition between the 4th partial range and the 6th partial range.

SAT IV users should call Inventronics to get the latest update for their SAT IV.    They can then update their own SAT IVs using the SAT UPdater program and the USB port on their SAT IV. Inventronics will send the Updater program, the update, and complete instructions for updating.

Leave a Reply

Your email address will not be published. Required fields are marked *

Piano Tuner Customers Say: