Refining FAC Tunings: Procedures and Best Practices

Refining FAC Tunings: Procedures and Best Practices

This document provides a detailed guide for refining FAC tunings using the AccuTuner IV, emphasizing recommended settings and step-by-step procedures to achieve accurate results. It introduces the “A Multiplier Default” parameter, advises setting it to 0.8 for optimal double octave contraction, and explains how midrange stretch adjustments can be made for precision tuning. The outlined process includes making corrections in the tenor register, ensuring each step is based on technical guidance for reliable and consistent outcomes.

Introduction

This section outlines a comprehensive approach for refining FAC tunings using the AccuTuner IV.

Setting the A Multiplier Default

The “A Multiplier Default” parameter was introduced to help align an FAC tuning’s A4 note closely with the standard A440 pitch.   If necessary, the “A Multiplier Default”  can also be adjusted to expand the stretch. Modifying the midrange stretch offers precise control over the FAC tuning process.

Step-by-Step Measurement and Correction Procedure

1. Tune A4 to A440 and Measure the 4th Partial

Begin by tuning A4 to A440. Record the location of its 4th partial  This value is necessary for later corrections, particularly after making PCC adjustments in the treble register.

2. Measure and Store FAC Numbers

Measure all FAC numbers as usual and save the tuning data to a memory page. This ensures the data can be reliably referenced during the tuning process.

3. Lower the Tenor Partial Change (from B2/C3 to G#2/A2)

Lowering the tenor partial change helps eliminate discrepancies within the temperament region, supporting dependable aural verification. On shorter scale pianos, this adjustment may move the partial change onto the bass bridge. Consult instructional materials for details on lowering the tenor partial change.

4. Utilize the Partial Change Correction Feature

Begin at the treble partial change (B5/C6), and correct any error there with the PCC feature.   Review and adjust the other partial change above A4 (B4/C5) in the FAC tuning. Then, use the PCC’s ‘C8 adjustment’ to correct and refine A4’s placement. Complete the process by correcting the tenor partial change now located between G#2/A2.

5. Verify FAC Measurement Consistency

After storing FAC numbers, cross-check measured values for consistency, focusing on areas using the same partials. Early identification of anomalies allows for timely corrections. If discrepancies arise, review the measurement process and repeat readings as needed for accuracy. Once all corrections are implemented, the FAC tuning will be free from inconsistencies caused by transitional errors at partial changes.

Advanced Tuning Techniques

Resolving partial discrepancies enables more accurate tuning in the A2–A4 range, and allows for accurate optimizing of the midrange stretch. Recommended notes for assessment are A2, D3, E3, A3, D4, E4, and A4. Once a decision has been made to either contract or expand the stretch in the midrange, the Double Octave Beat (DOB) function is a global parameter affecting overall stretch.    Before making subjective adjustments, verify tuning accuracy and confirm with at least two aural indications. Where tonal irregularities persist, consider instrument-specific scaling factors rather than excessive corrections to the tuning’s settings.

**Once key reference notes are established, creating a tailored tuning sequence can increase operational efficiency. Instructions for this process are provided in the relevant instructional materials.**

Technical Guidance for Double Octave Adjustments

After lowering the tenor partial change, the setting for A2 may be below -4.0 c. (when using the 4th Partial).   According to Al Sanderson (Appendix E, SAT Manual), if A2 falls below -4.0 cents, the double octave may be excessively wide.  Some pianos do require an A2 setting lower than -4.0 settings for optimal compromise, but most don’t.   Critical listening to intervals such as A2/E3 fifth, A2/A3 octave, and A2/E4 twelfth is advised. Adjust DOB to contract the stretch and retune as necessary.

The DOB function on AccuTuner enables fine-tuning of the and adjusting of the stretch: each 0.1 DOB lowers A3 by 0.2 cents and A2 by 0.4 cents—positive DOB values widen and negative values contract the stretch.

After lowering the tenor partial change, applying PCC, and confirming A4 at A440 using the C8 tweak, use DOB if A2 is at -4.0 cents or lower. Adjustments made with DOB do not compromise PCC results.

Guidelines for Setting the A2 Location

To determine the optimal A2 setting, start by tuning A4 to A440, then experiment with progressively wider A2–A4 double octaves.  Starting at a 1.0 c. wide A2/A4, widen it by .5 c. at a time and listen to how it sounds (from 1 to 6 cents). There will be a width where the interval becomes too wide for your  aural ‘taste’, and will then serve as your personal reference. An analysis of approximate 300 tunings shows the average A2 setting is around -3.3 cents.  Some instruments require more extreme values nearing -6.5 cents.

Recognizing and accommodating these requirements is vital for professional outcomes. The AccuTuner provides specialized tools for challenging scenarios, but thoughtful and careful judgment is essential in their use.

Every piano is unique; identifying the ideal A2 value requires hands-on experimentation. Following the outlined process ensures ongoing improvement with minimal additional effort.