Overview of FAC Treble Stretch
FAC tuning utilizes a double octave stretch for tuning the treble section of the piano. In this approach, when tuning A6, A4 is used as the reference note to determine the optimal pitch for A6. If additional stretch in the treble is desired, alternative reference notes can be employed. For example, reference notes such as D4, A3, and D3—once tuned to the FAC system—can be used to increase the stretch. The principle is straightforward: the greater the interval between the reference note and the note being tuned, the more pronounced the stretch. Using D4 as a reference for A6, for instance, tunes A6 as a double octave plus a fifth from D4, while referencing A3 tunes A6 as a triple octave from A3.
Step-by-Step: Increasing Treble Stretch
For those new to enhancing treble stretch, it is recommended to begin by using D4 as the reference note for A6. Once D4 is tuned according to FAC, set the tuner to A6 and play D4. Observe the rotation of the indicator lights; typically, the lights will suggest that the FAC setting for A6 is flat. Add enough DOB (Double Octave Beat) until the lights stop rotating when D4 is played. This adjustment sets the DOB amount required for tuning all notes above A4 in the treble. Be sure to remove the DOB setting when tuning notes below A4.
Aural Checks and Fine-Tuning
Aural checks are essential for verifying the new treble stretch. Use as many checks as necessary to ensure the treble is properly stretched. Recommended notes for checking A6 include D4, A4, D5, A5, and D6, with particular attention paid to the fifth interval between D6 and A6. Incrementally increase the DOB, perhaps in 0.1 steps, until a satisfactory stretch is achieved for all the chosen reference notes. Sometimes, raising A6 above the initial double octave plus fifth setting yields an even better result. Although the double octave plus fifth is a safe starting point, further experimentation and listening may reveal that additional stretch is preferable. Some tuners may opt for a compromise between the double octave plus fifth (using D4) and the triple octave (using A3), alternating between these reference notes to find an optimal setting for A6.
Choosing Reference Notes for Stretch
Using D3 or A3 to locate A6 is advised only for longer scale pianos, as on shorter scales D3 can be a poor reference. For longer scales, D3 may serve well in combination with D4 to find optimal locations for higher notes such as A5, A6, and A7. When employing D3, consider its characteristics, as it might be a trichord under high tension or a wound bichord, especially in the tenor area of shorter pianos. With experience, it becomes clear whether D3 is suitable for use as a reference.
Before using D3 and D4 as references, both should be tuned to the FAC system. Set the tuner to A6, alternately play D3 and D4, and observe the light rotation. Another method is to stop the lights at each note, record both settings, and then choose a midpoint as the SAT setting.
Finalizing Treble Stretch Settings
Once the preferred stretch for A6 is determined using D3 and D4, set the DOB to reflect this adjustment. Continue tuning and aural checking with notes such as D5, E5, A5, D6, E6, and A6, focusing on fifths but also listening to octaves. If any interval suggests further modification, easily adjust the DOB to achieve the desired stretch. Over time, experience and repeated tuning across different pianos will help develop a sense for optimal treble stretching. Sometimes, a technician’s ear may lean towards a more familiar, lesser stretch, but listening critically can reveal the benefits of a more expansive treble.
The DOB setting determined for treble should be applied exclusively to notes from A4 to C8.
DOB Ranges and Tuning Devices
Different SAT models have varying DOB ranges. The original DOB range was +/- 2.0, applicable to SAT models I, II, and III. The Standard Model SAT IV also typically features a +/- 2.0 range, which can be checked by holding down the BluShift and Cents UP buttons. The SAT IV “980” model originally had this same range, but firmware updates have expanded the DOB range to +/- 4.0 or even +/- 10.0, depending on the update. This wider range enables more significant treble stretching, such as tuning a triple octave at A7, which is not possible with the original +/- 2.0 range.
To check for a firmware update for your SAT IV, contact Inventronics. Once the update file is obtained, it can be installed via PC.
Using Multiple DOB Settings for High Treble
After establishing the DOB setting for A6, additional DOB can be applied to further stretch the highest octave (A6 to C8). To find a suitable setting for A7, use A4 as the reference note for a triple octave, or D4 for a triple octave plus fifth. Alternately play A4 and D4 with the tuner set to A7 to identify a compromise setting, usually favoring the higher pitch. Write down the selected A7 setting and calculate the DOB needed to achieve it. With only +/-2.0 DOB, reaching the higher A7 setting may be impossible, but expanded ranges on updated SAT models make it feasible.
Each 0.1 DOB increment raises A7 by approximately 0.6 cents. Adjust the DOB incrementally for each note above A6, potentially adding 0.1 DOB per note, every second note, or in larger steps as needed, so that by A7 the desired DOB is reached. Use this setting for the highest notes (A7 to C8).