Playing string harmonics produces high pitched tones, often compared in timbre to a whistle or flute.
[1][2] Overtones can be isolated "by lightly touching the string with the finger instead of pressing it down" against the fingerboard (without stopping).
[2] For some instruments this is a fundamental technique, such as the Chinese guqin, where it is known as fan yin (泛音, lit.
(Resulting harmonic sound: two octaves and a major third above the first finger or new fundamental.
This results in a high-pitched sound which is particularly discernible on an electrically amplified guitar as a "squeal".
The note is fretted as usual, but instead of striking the string the excitation energy required to sound the note is achieved by tapping at a harmonic nodal point.
The open string technique can be extended to artificial harmonics.
This technique is used by effect devices producing a magnetic field that can agitate fundamentals and harmonics of steel strings.