Key signature A minor as each accidental may be notated explicitly as required, or the piece may be modal or atonal. An example is Bartók's Piano Sonata, which has no fixed key and is highly chromatic. If not bound by common practice conventions, microtones can also be notated in a key signature; which microtonal symbols are used depends on the system. The common practice period conventions are so firmly established that some musical notation programs have been unable to show nonstandard key signatures until recently. The use of a one-flat signature developed in the Medieval period, but signatures with more than one
Music of southern China Perfect-fourth transposition of the melody ("fan") also occurs, though the tonal centre remains constant. Four or five main modes ("diao") are traditionally identified. However, while elsewhere in China such modes are mainly defined by absolute pitch and by the degree of the pentatonic scale that is taken as the key-note (thus setting the intervals of the scale), the xianshi conception of mode, rather like the Indian raga system, includes motif, ornament and intonation. Pitch is not absolute but the scale is usually constructed on a key-note approximating to western concert F – F#. Modes are pentatonic but all derive from