A split sharp is a kind of key found in some early keyboard instruments, such as the harpsichord, clavichord, or organ. It is a musical key divided in two, with separately depressible front and back sections, each sounding its own pitch. The particular keys that were split were those that play (C♯/D♭, D♯/E♭, F♯/G♭, G♯/A♭, A♯/B♭) on the standard musical keyboard (the "black keys" on a modern piano).
Second, in older music, tuning was generally not done by equal temperament, which treats note pairs such as A♯ and B♭ as the same pitch. Instead, they were assigned slightly different pitches on enharmonic keyboards (particularly in "meantone temperament"). This allowed certain musical intervals, such as the major third, to sound closer to their ideal just value, hence more closely tuned to just intonation.[a]
In modern usage, split sharps are usually the method of choice for custom keyboards that play 19 equal temperament, which, like meantone, uses different pitches for sharps and flats that are enharmonic in the standard 12 tone.
- For a recent defense of the older tuning practices, see Duffin, Ross (2006) How Equal Temperament Ruined Harmony (and Why You Should Care) W.W. Norton & Co. ISBN 0-393-06227-9.
- See: www.n-ism.org. "Historically, 19-tone keyboards have been constructed...with the rear of the divided black keys often raised."
- Kottick, Edward L. and George Lucktenberg (1997) Early keyboard instruments in European museums. Bloomington: Indiana University Press.