Pressing the string against the fret reduces the
vibrating length of the string to that between the
bridge and the next fret between the fretting finger and the bridge. This is damped if the string were stopped with the soft fingertip on a
fretless fingerboard. Frets make it much easier for a player to achieve an acceptable standard of
intonation since the frets determine the positions for the correct notes. Furthermore, a fretted fingerboard makes it easier to play
chords accurately. A disadvantage of frets is that they restrict
pitches to the
temperament defined by the fret positions. A player may still influence
intonation, however, by pulling the string to the side to increase string tension and raise the pitch. This technique (commonly called "
bending") is often used by electric
guitarists of all genres, and is an important part of
sitar playing. On instruments with frets that are thicker off the fingerboard, string tension and pitch vary with finger pressure behind the fret. Sometimes a player can pull the string toward the
bridge or
nut, thus lowering or raising the string tension and pitch. However, except for instruments that accommodate extensive string pulling, like the sitar, much less influence on intonation is possible than on unfretted instruments.
Equal temperament Since the
intonation of most modern western fretted instruments is in
12 tone equal temperament, the
ratio of the distances of two consecutive frets to the bridge is Twelfth root of two|\sqrt[12]{2} (the twelfth root of two), or approximately 1.059463. Theoretically, the twelfth fret should divide the string in two exact
halves. To compensate for the increase in string tension when the string is pressed against the frets, the bridge position is adjusted slightly so the 12th fret plays exactly in
tune.
Non-equal temperament ; note
microtonal frets between semitones. Many instruments' frets are not spaced according to the semitones of equal temperament. Some examples are: •
Appalachian dulcimer with frets in a
diatonic scale; • the Turkish
Saz with frets spaced according to the
Makam system of
Turkish folk music; • the Arabic
buzuq with frets spaced according to the
Arabic maqam system; • the Persian
setar and
tar with frets spaced according to the Persian
Dastgah system; • the Turkish
tanbur with as many as 5 frets per semitone, to cover all of the
commas of the Turkish
Makam system. == Variations ==