Perfect fourth

The perfect fourth or diatessaron, abbreviated P4, is the interval between the first note (the root or tonic) and the fourth note (subdominant) in a major scale. It is the inversion of the perfect fifth.

Related Topics:
Interval - Major scale - Inversion - Perfect fifth

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A perfect fourth in just intonation corresponds to a pitch ratio of 3:4, while in an equal tempered tuning, a perfect fourth is equal to five semitones, a ratio of 1:25/12 (approximately 1:1.3348), or 500 cents, about 1.955 cents wide.

Related Topics:
Just intonation - Equal tempered - Cent

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The perfect fourth, although considered a perfect interval like the unison, octave, and perfect fifth, is actually considered a dissonance.

Related Topics:
Unison - Octave - Perfect fifth

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Conventionally, the strings of a double bass and a bass guitar are tuned by intervals of perfect fourths, while all strings but one of a guitar are tuned to intervals of perfect fourths.

Related Topics:
Double bass - Bass guitar

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