Vide: https://www.speech.kth.se/music/5_lectu...dinal.html

(I do wonder, in addition, if the age of the strings has any effect. Would rust and stretching affect the pitch or at least the amplitude of longitudinal vibrations? The envelope? Or would they instead affect the main vibrations, so we hear the longitudinal vibrations differently? Both, I would guess, but perhaps not in the same way, or to the same degree...)

I have come across this video with a restrung NY Steinway. Key 8 (listen around 6 seconds in) has a different longitudinal mode, about 3 semitones flatter than what is heard in Pianoteq at the default string length. To match the L-mode pitch to the video, I had to increase the string length to ~3.15m. While this fixes the discrepancy, it also changes the inharmonicity, which might not be desirable if one wants to match to a specific piano, e.g. a piano in the house, a highly requested piano, or an exotic 330+cm beast (Borgato 333, Rubenstein R-371, Klavins VCG, etc.)

Allowing tunable L-modes would allow string-length changes to not sound dissonant due to out-of-tune L-modes fouling an otherwise fine preset, as well as give a greater range of tonal possibilities for the hardcore fxp tweakers.