perfect 4th, perfect fourth, p4

The interval which encompasses 4 degrees of a diatonic scale. It is usually close in size to the frequency ratio 4:3, which is ~498.0449991 cents.

In the usual 12-EDO tuning, the perfect 4th encompasses 5 semitones, and is thus exactly 500 cents.

[from Joe Monzo, JustMusic: A New Harmony]

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The interval 4/3 in Just Intonation or the closest approximation to 498 cents (¢) in an equal temperament.

The Diatesseron in Greek theory.

[from John Chalmers, Divisions of the Tetrachord]

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