Мұзыкалық нотациядағы өзгерту белгілері

Musical note not in the current key signature

In musical notation, an accidental is a symbol that indicates an alteration of a given pitch. The most common accidentals are the flat and the sharp , which represent alterations of a semitone, and the natural , which cancels a sharp or flat. Accidentals alter the pitch of individual scale tones in a given key signature; the sharps or flats in the key signature itself are not considered accidentals. An accidental raises or lowers the following note—and any repetition of it in the same measure—from its regular pitch, overriding the key signature. A sharp raises a note's pitch by a semitone and a flat lowers it by a semitone. Double sharps or flats may also be used, which alter the unmodified note by two semitones. Accidentals apply to all subsequent instances of the same note within the measure unless canceled by another accidental. If a note with an accidental is tied, the accidental continues to apply, even if the note it is tied to is in the next measure. If a note has an accidental and the note is repeated in a different octave within the same measure the accidental is usually repeated, although this convention was not always universal. The modern accidental signs derive from the two forms of the lower case letter b used in Gregorian chant manuscripts to signify the two pitches of B, the only note that could be altered. The "round" b became the flat sign, while the "square" b diverged into the sharp and natural signs.

Double accidentals raise or lower the pitch of a note by two semitones (or a whole tone). This applies to the written note, ignoring key signature. An F with a double sharp applied raises it a whole step so it is enharmonically equivalent to a G.

Usage varies on how to notate the situation in which a note with a double flat (or sharp) is followed in the same octave in the same measure in the same staff by a note with a single sharp (or flat). Some publications canceling the double accidental, such as simply using the conventional sign like a flat or sharp, etc., for the latter note, (as the modern practice,) whereas others use a combination such as a natural and flat or natural and sharp (shown below), instead, (as the older practice). In addition, also refer to the documentation: 'Double natural'

Composers of microtonal music have developed a number of notations for indicating the various pitches outside of standard notation. One such system for notating quarter tones, used by the Czech Alois Hába and other composers, is shown. In the 19th and early 20th centuries, when Turkish musicians switched from their traditional notation systems—which were not staff based—to the European staff based system, they refined the European accidental system so they could notate Turkish scales that use intervals smaller than a tempered semitone. There are several such systems, which vary as to how they divide the octave they presuppose or the graphical shape of the accidentals. The most widely used system (created by Rauf Yekta Bey) uses a system of four sharps (roughly +25 cents, +75 cents, +125 cents and +175 cents) and four flats (roughly −25 cents, −75 cents, −125 cents and −175 cents), none of which correspond to the tempered sharp and flat. They presuppose a Pythagorean division of the octave taking the Pythagorean comma (about an eighth of the tempered tone, actually closer to 24 cents, defined as the difference between seven octaves and 12 just intonation fifths) as the basic interval. The Turkish systems have also been adopted by some Arab musicians. Ben Johnston created a system of notation for pieces in just intonation where the unmarked C, F, and G major chords are just major chords (4:5:6) and accidentals create just tuning in other keys. Between 2000 and 2003, Wolfgang von Schweinitz and Marc Sabat developed the Extended Helmholtz Ellis Just Intonation (JI) pitch notation, a modern adaptation and extension of the notation principles first used by Hermann von Helmholtz, Arthur von Oettingen, and Alexander John Ellis that some other musicians use for notating extended just intonation.

The three principal symbols indicating whether a note should be raised or lowered in pitch are derived from variations of the small letter b: the sharp and natural signs from the square "b quadratum", and the flat sign from the round "b rotundum". The different kinds of B were eventually written differently, so as to distinguish them in music theory treatises and in notation. The flat sign derives from a round b that signified the soft hexachord, hexachordum molle, particularly the presence of B. The name of the flat sign in French is bémol from medieval French bé mol, which in modern French is bé mou ("soft b"). The natural sign and the sharp sign derive from variations of a square b that signified the hard hexachord, hexachordum durum, where the note in question is B. The name of the natural sign in French is bécarre from medieval French bé quarre, which in modern French is bé carré ("square b"). In German music notation, the letter B or b always designates B while the letter H or h – a deformation of a square b – designates B. In the High Middle Ages, a widespread musical tradition was based on the hexachord system defined by Guido of Arezzo. The basic system, called musica recta, had three overlapping hexachords. Change from one hexachord to another was possible, called a mutation. A major problem with the system was that mutation from one hexachord to another could introduce intervals like the tritone that musicians of the time considered undesirable. To avoid the dissonance, a practice called musica ficta arose from the late 12th century onward. This introduced modifications of the hexachord, so that "false" or "feigned" notes could be sung, partly to avoid dissonance. At first only B could be flattened, moving from the hexachordum durum (the hard hexachord) G–A–B–C–D–E where B is natural, to the hexachordum molle (the soft hexachord) F–G–A–B–C–D where it is flat. The note B is not present in the third hexachord hexachordum naturale (the natural hexachord) C–D–E–F–G–A. Strictly speaking the medieval signs and indicated that the melody is progressing inside a (fictive) hexachord of which the signed note is the mi or the fa respectively. That means they refer to a group of notes around the marked note, rather than indicating that the note itself is necessarily an accidental. For example, when a semitone relationship is indicated between F and G, either by placing a mi sign on F or a fa sign on G, only the context can determine whether this means, in modern terms, F G or F G, or even F–G. The use of either the mi sign on F or the fa sign on G means only that "some kind of F goes to some kind of G, proceeding by a semitone". As polyphony became more complex, notes other than B required alteration to avoid undesirable harmonic or melodic intervals (especially the augmented fourth, or tritone, that music theory writers referred to as diabolus in musica, i. e., "the devil in music"). Nowadays "ficta" is used loosely to describe any such un notated accidentals. The implied alterations can have more than one solution, but sometimes the intended pitches can be found in lute tablatures where a fret is specified. The convention of an accidental remaining in force through a measure developed only gradually over the 18th century. Before then, accidentals only applied to immediately repeated notes or short groups when the composer felt it was obvious that the accidental should continue. The older practice continued in use well into the 18th century by many composers, notably Johann Sebastian Bach. The newer convention did not achieve general currency until early in the 19th century.