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Tritone

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A tritone is a specific musical interval that spans exactly three whole tones. In the system of 12-tone-equal temperament, this interval divides an octave exactly in half. An octave consists of 12 semitones, or 1200 cents, meaning a tritone covers 6 semitones or 600 cents.

Comparison of tritones
Comparison of tritones

Because of this symmetry, the tritone plays a special role in various musical structures. It is often described as a restless or unstable sound. This instability makes it a vital tool for composers looking to create tension or movement within a piece of music.

Music theorists use two different ways to define what counts as a tritone. Under a narrow definition, only the augmented fourth is considered a tritone. An augmented fourth is created by widening a perfect fourth by one semitone without changing the letter names. Under this narrow view, a diatonic scale like C major contains only one tritone, which is F–B. However, a broad definition is much more inclusive. This version includes augmented fourths and diminished fifths, which are created by narrowing a perfect fifth by one semitone.

This broader view means a diatonic scale actually contains two tritones per octave, such as F–B and B–F in C major. It can even include rare intervals like doubly augmented thirds or doubly diminished sixths.

The way a tritone functions depends heavily on the type of scale being used. In a major scale, the augmented fourth appears between the fourth and seventh scale degrees. In a natural minor scale, a diminished fifth occurs between the second and sixth degrees. Harmonic minor scales are more complex, containing both an augmented fourth and a diminished fifth. Melodic minor scales change depending on whether the melody is ascending or descending.

Scales that contain these intervals are called tritonic, while those without them are called atritonic.

In traditional functional harmony, the tritone is a primary source of dissonance. This dissonance creates a strong urge for the notes to move toward a resolution. For example, diminished triads and dominant seventh chords contain tritones that push toward the tonic, or the home key. Augmented sixth chords also use tritones spelled as augmented fourths. The Italian and German sixth chords each contain one augmented fourth. In contrast, the French sixth chord is built from two superposed augmented fourths that are a major second apart.

Tritone substitution
Tritone substitution

These chords often resolve by moving in contrary motion to create a sense of stability.

The history of the tritone is marked by a long period of avoidance. During the Middle Ages and the Renaissance, it was classed as a dissonance and often rejected. Medieval ecclesiastical singers frequently avoided the interval in religious music. Early theorists like Guido of Arezzo even suggested moving the hexachord system to avoid the F–B tritone. Some historical accounts even refer to the interval as "the devil in music."

While there are no known records of singers being punished by the Church for using it, the association with the devil became a lasting cultural idea. This nickname often referred to the clash between notes like "mi" and "fa" from adjacent hexachords.

As music moved into the Baroque and Classical periods, composers began to use the tritone in a controlled way. They utilized it within the tension-release mechanism of tonal music. By the Romantic period, composers used the interval more freely to exploit its expressive and dark connotations. Franz Liszt used the tritone to suggest the atmosphere of Hell in his Dante Sonata. Richard Wagner used timpani tuned to C and F to create a brooding feeling in the second act of his opera, Siegfried.

Siegfried Act 2 prelude
Siegfried Act 2 prelude

Hector Berlioz also used massive B and F chords to create a "tonal wrench" during a transition in his work, Faust.

In the 20th century, the tritone became a neutral structural tool rather than just a source of tension. Claude Debussy used the interval to convey sudden, overwhelming power in his cantata, "La Damoiselle Elue."

In twelve-tone music and serialism, the tritone is often viewed as a neutral interval. It can play a major role in structural systems, such as the axis system used by Béla Bartók. Benjamin Britten also utilized the interval for emotional impact. In his "War Requiem," he used a tritone between C and F-sharp to create a somber and ambiguous atmosphere.

Britten - Serenade prologue
Britten - Serenade prologue

Even in popular music, the tritone remains influential, such as in Leonard Bernstein's "West Side Story."

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🖼️ Images & Media (18)
File:Siegfried Act 2 prelude.png
Siegfried Act 2 prelude.png
Wagner, Prelude to Act 2 of Siegfried.wav
File:Debussy la Damoiselle Fig 30.png
Debussy la Damoiselle Fig 30.png
Debussy, la Damoiselle Elue, Fig 30.wav
File:Debussy Quartet 2nd movement, bars 140-7.png
Debussy Quartet 2nd movement, bars 140-7.png
Debussy Quartet 2nd movement, bars 140-7.wav
File:Tritone substitution.png
Tritone substitution.png
Tritone substitution.mid
File:Comparison of tritones.png
Comparison of tritones.png
Just diminished fifth on C.mid
Just augmented fourth on C.mid
Pythagorean augmented fourth on C.mid

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