Introduced in 2019, 3-part tuning is the most significant change to the generation of TuneLab tuning curves since its launch in 2001.
3-part tuning starts with the selection of three different intervals for the bass, treble, and mid-range of the scale. The calculation of the tuning curve proceeds note-by-note from the mid-range outward, just as in aural tuning, gradually blending into the intervals chosen for the bass and treble. It is especially well-suited to perfect 12th tunings by selecting 12ths for all three intervals.
The note-by-note calculation is better able to take advantage of more inharmonicity readings when they are available, and thus follow the irregularities in the inharmonicity pattern of non-ideal pianos. 3-part tuning will become the default mode for TuneLab, while still maintaining the option of using the “classic” TuneLab tuning curve defined by four parameters and conforming to just the bass and treble interval selections.
The graph above shows a typical tuning curve generated by 3-part tuning. You can change the bass, middle, and treble intervals, and you can vary the positioning of the middle interval. These selections are separate from the bass and treble interval selections in the "classic" TuneLab tuning curve. Those older interval selections do not affect the tuning curve in 3-part tuning mode, but they still determine the intervals displayed in the deviation curve. In this way you can use the classic TuneLab interval selections or evaluate a 3-part tuning curve in terms of intervals other than the ones that 3-part tuning is using.