Perfect 4th

5 semitones — open and neutral, the inversion of the 5th

Degree 4Solfège: faNotation: P4

The perfect 4th is an interval of 5 semitones — the inversion of the perfect 5th. It is consonant — open, neutral, slightly suspended. It appears in the minor pentatonic and every major mode except lydian, and is derived from the 4th harmonic (4:3).

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The instrumentTap a note to hear it.
The perfect 4th in the harmonic series
f2f3f3f completes 3 cycles in one period of the sum3 cycles4f4f completes 4 cycles in one period of the sum4 cycles5f6f7f8f9f10f11f12f13f14f15f16fsum4:3 — the higher note vibrates 4 times for every 3 of the lower: harmonics 4 and 3 of one fundamental4:34: the perfect 4th — the interval's degree above the root, as the app writes it4The sum repeats every 3 cycles of 3f — the shorter this is, the more simply the two notes fit together, and the more consonant the intervalrepeats every 3 cycles16 cycles of 3f
Harmonic seriesEach row is one harmonic of the note — n times the fundamental's frequency, about 1/n of its strength — faster and fainter as it climbs. The rows in ink are where the chosen interval first arises. The bottom row is the one your ear actually receives: those rows added, a single wave. The shaded band is one repeat of it — the shorter that pattern, the sooner the ear settles on it as one sound. Harmonics 3 and 4 — the ratio 4:3: a perfect 4th. Together they repeat every 3 cycles of the lower note — the shorter that pattern, the sooner your ear has heard it come round enough times to settle on one sound. Equal temperament tunes it 2¢ wider.

Related

Contained byIntervalsRelatedSolfègePerfect 5thConsonanceDerived fromHarmonic Series