Perfect fifth

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Template:Infobox Interval The perfect fifth or diapente is a musical interval which is responsible for the most consonant, or stable, harmony outside of the unison and octave. It is a valuable interval in chord structure, song development, and western tuning systems. The prefix perfect identifies it as belonging to the group of perfect intervals (Perfect fourth, Perfect octave) so called because of their extremely simple pitch relationships resulting in a high degree of consonance. The perfect fifth is historically relevant because it is the first accepted harmony (besides the octave) of gregorian chant, a very early formal music composition. The perfect fifth occurs on the root of all major and minor chords (triads) and their extensions. It is one of three musical intervals that span five diatonic scale degrees; the others being the diminished fifth, which is one semitone smaller, and the augmented fifth, which is one semitone larger. The Solfege of the perfect fifth is "Do - So". A helpful way to recognize a perfect fifth is to hum the starting of twinkle twinkle little star, which is a familiar perfect 5th. The perfect fifth is abbreviated as P5 and its inversion is the perfect fourth.

1 Use in chords
2 Use in tuning and tonal systems
3 See also
4 External link

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Use in chords

Due to its high level of consonance, the perfect fifth contributes very little to the overall harmonic effect of any chords containing it (power chords excepted). In any situation that necessitates the omission of notes from a chord, such as for practical reasons of fingering, for example, the note forming the perfect fifth above the chord's root can often be safely omitted, its absence being barely, if at all, noticeable.

A bare fifth or open fifth is a chord containing only a perfect fifth with no third. The closing chord of Mozart's Requiem is an example of a piece ending on an open fifth, though these "chords" are common in Christian Sacred Harp singing and throughout rock music, including hard rock, metal, and punk music, where they are called power chords if played with distortion or overdrive. Power chords often have octave doubling (i.e. their bass note is doubled one octave higher, e.g. F3-C4-F4).

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Use in tuning and tonal systems

A perfect fifth in just intonation, a just fifth, corresponds to a pitch ratio of 3:2, while in 12-tone equal temperament, a perfect fifth is equal to seven semitones, a ratio of 1:2^7/12 (approximately 1.4983), or 700 cents, about two cents smaller.

The just perfect fifth, together with the octave, forms the basis of Pythagorean tuning.

The circle of fifths is a model of pitch space for the chromatic scale (chromatic circle) which considers nearness not as adjacency but as the number of perfect fifths required to get from one note to another.

The strings on violins, violas, and cellos are all tuned to perfect fifths unless in scordatura.

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