Other namesaugmented fourth, diminished fifth
AbbreviationTT, A4, d5
Interval class6
Just interval25:18, 36:25, 45:32, 64:45, 7:5, 10:7, 13:9...
Equal temperament600
24 equal temperament600
Just intonation569, 631; 590, 610; 583, 617; 563, 637 ...

In music theory, the tritone is defined as a musical interval composed of three adjacent whole tones.[1] For instance, the interval from F up to the B above it (in short, F–B) is a tritone as it can be decomposed into the three adjacent whole tones F–G, G–A, and A–B. According to this definition, within a diatonic scale there is only one tritone for each octave. For instance, the above-mentioned interval F–B is the only tritone formed from the notes of the C major scale. A tritone is also commonly defined as an interval spanning six semitones. According to this definition, a diatonic scale contains two tritones for each octave. For instance, the above-mentioned C major scale contains the tritones F–B (from F to the B above it, also called augmented fourth) and B–F (from B to the F above it, also called diminished fifth, semidiapente, or semitritonus).[2] In twelve-equal temperament, the tritone divides the octave exactly in half.

In classical music, the tritone is a harmonic and melodic dissonance and is important in the study of musical harmony. The tritone can be used to avoid traditional tonality: "Any tendency for a tonality to emerge may be avoided by introducing a note three whole tones distant from the key note of that tonality."[3] Contrarily, the tritone found in the dominant seventh chord helps establish the tonality of a composition. These contrasting uses exhibit the flexibility, ubiquity, and distinctness of the tritone in music.

The condition of having tritones is called tritonia; that of having no tritones is atritonia. A musical scale or chord containing tritones is called tritonic; one without tritones is atritonic.

Augmented fourth and diminished fifth

Chromatic scale on C: full octave ascending and descending About this soundPlay in equal temperament .
Full ascending and descending chromatic scale on C, with tritone above each pitch. Pairs of tritones that are inversions of each other are marked below.
The augmented fourth between C and F and the diminished fifth between C and G are enharmonically equivalent intervals. Both are 600 cents wide in 12-TET. About this soundPlay .

Since a chromatic scale is formed by 12 pitches (each a semitone apart from its neighbors), it contains 12 distinct tritones, each starting from a different pitch and spanning six semitones. According to a complex but widely used naming convention, six of them are classified as augmented fourths, and the other six as diminished fifths.

Under that convention, a fourth is an interval encompassing four staff positions, while a fifth encompasses five staff positions (see interval number for more details). The augmented fourth (A4) and diminished fifth (d5) are defined as the intervals produced by widening the perfect fourth and narrowing the perfect fifth by one chromatic semitone.[4] They both span six semitones, and they are the inverse of each other, meaning that their sum is exactly equal to one perfect octave (A4 + d5 = P8). In twelve-tone equal temperament, the most commonly used tuning system, the A4 is equivalent to a d5, as both have the size of exactly half an octave. In most other tuning systems, they are not equivalent, and neither is exactly equal to half an octave.

Any augmented fourth can be decomposed into three whole tones. For instance, the interval F–B is an augmented fourth and can be decomposed into the three adjacent whole tones F–G, G–A, and A–B.

It is not possible to decompose a diminished fifth into three adjacent whole tones. The reason is that a whole tone is a major second, and according to a rule explained elsewhere,[where?] the composition of three seconds is always a fourth (for instance, an A4). To obtain a fifth (for instance, a d5), it is necessary to add another second. For instance, using the notes of the C major scale, the diminished fifth B–F can be decomposed into the four adjacent intervals

B–C (minor second), C–D (major second), D–E (major second), and E–F (minor second).

Using the notes of a chromatic scale, B–F may be also decomposed into the four adjacent intervals

B–C (major second), C–D (major second), D–E (major second), and E–F (diminished second).

Notice that the latter diminished second is formed by two enharmonically equivalent notes (E and F). On a piano keyboard, these notes are produced by the same key. However, in the above-mentioned naming convention, they are considered different notes, as they are written on different staff positions and have different diatonic functions within music theory.

Other Languages
български: Тритонус
català: Tríton
čeština: Tritón
dansk: Tritonus
Deutsch: Tritonus
eesti: Tritoon
español: Tritono
français: Triton (musique)
한국어: 셋온음
հայերեն: Տրիտոն
hrvatski: Tritonus
íslenska: Tónskratti
italiano: Tritono
lietuvių: Tritonis
Nederlands: Tritonus
日本語: 三全音
norsk: Tritonus
português: Trítono
slovenčina: Tritón (hudba)
slovenščina: Tritonus
suomi: Tritonus
svenska: Tritonus
українська: Тритон (інтервал)
中文: 增四度