If, as one person put it, when tuning a unison, we are changing the "vowel" sound, what does this really mean? Differences between vowels are caused by different strengths of various partials, rather than by differences in inharmonicity. So how do you change the strength of a partial by making small tension adjustments? The only thing I can think of is that there is a range of tensions where the fundamentals will stay in phase due to sympathetic vibrations, and within this range, other partials may be aligned or misaligned, and this alignment/misalignment affects the net strength of the partial by causing it to be reinforced or not. I have tuned unisons using ETD so that the fundamentals are well- matched, and the resulting sound to me is "hot" (particularly if done across the whole piano), like someone turned the treble knob all the way up, emphasizing some high partials (think tape hiss). Aurally tuned unisons do not have this characteristic. So is the well-tuned unison designed to de-emphasize particular partials? This would seem to be the case. Experiment: tune 2 strings with ETD so fundamentals are in phase. Measure each partial (inharmonicity is as good as any, just need some relative pitch in cents). Retune by ear and remeasure. Which partials align? Which don't? What does the spectral display show for the strength of the partials when the strings are played together? In particular, which partials decreased in strength? -Mark
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