Playing a string harmonic (a flageolet) is a string instrument technique that uses the nodes of natural harmonics of a musical string to isolate overtones. Playing string harmonics produces high pitched tones, often compared in timbre to a whistle or flute. Overtones can be isolated "by lightly touching the string with the finger instead of pressing it down" against the fingerboard (without stopping). For some instruments this is a fundamental technique, such as the Chinese guqin, where it is known as fan yin (泛音, lit. "floating sound"), and the Vietnamese đàn bầu.