The musical interval of a perfect fifth is the relationship between the first note (the root or tonic) and the fifth note in a major scale. It is the inversion of the perfect fourth.

It can be produced by starting on a high note and playing the fifth below or by starting on a low note and playing the fifth above.

A perfect fifth in just intonation corresponds to a pitch ratio of 2:3 or 1:1.5 while in an equal tempered tuning, a perfect fifth is equal to seven semitones, a ratio of 1:27/12 (approximately 1.4983), or 700 cents,two centss smaller.

The perfect fifth is considered the most consonant interval outside of the unison and octave.

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

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