Why Can a Clavichord Change Pitch After the Key Is Down?

On a modern piano, the hammer rebounds immediately after striking the string, so finger pressure cannot alter a note's pitch once the key is down. A clavichord works differently. The small metal tangent at the far end of the key strikes the string and remains against it until the finger releases the key. It both begins the vibration and defines one end of the string's speaking length.

Because this mechanical connection remains unbroken, a player can vary finger pressure slightly during a sustained note, changing string tension and the fundamental frequency. This produces the effect called Bebung. It is often described as vibrato, but it is neither repeated striking of a note on a modern piano nor quite the same as violin vibrato. What matters to the ear is not a large wavering pitch, but a very quiet tone acquiring breath and emphasis while it continues.

Acoustic experiments confirm that tangent velocity affects loudness, while pressure after the key has descended can also influence the fundamental frequency. This control comes with clear limits: the clavichord is extremely quiet, and excessive pressure can make pitch unstable. Its expressive character lies precisely in this narrow range of continuing contact between finger and string. For modern pianists, the comparison is instructive. A piano cannot reproduce Bebung, but that does not mean a long note is musically finished; balance, the entry of later notes and the handling of time can still give an unchangeable sound direction.

https://www.metmuseum.org/art/collection/search/503444
https://pubmed.ncbi.nlm.nih.gov/20968387/
https://www.hpschd.nu/clav.html