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Why can pressing a string against a fingerboard make a note slightly sharper?
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stringed instrument
A Japanese musician plucking the strings of a koto with the right hand to generate a pitch and pressing the strings with the left hand to alter the tone.
When you press a string against a fingerboard on a stringed instrument, the note produced can become slightly sharper than expected. This occurs because the act of pressing the string down to the fingerboard stretches the string, which slightly increases its length and tension.1
According to Mersenne’s laws, the frequency of a vibrating string is directly proportional to the square root of its tension. Because the downward pressure increases the tension, the resulting pitch is raised, making the note sound sharper than it would if the string remained at its original tension. This effect is a common challenge for instrument makers and players, who must account for these physical realities when setting up instruments or performing.21