4/1

Interval information

Ratio	4/1
Factorization	22
Monzo	[2⟩
Size in cents	2400¢
Names	4th harmonic, double octave, perfect fifteenth, tetrave, quadruple
Color name	wa 15th
FJS name	[math]\displaystyle{ \text{P15} }[/math]
Special properties	harmonic, highly composite harmonic
Tenney height (log2 nd)	2
Weil height (log2 max(n, d))	4
Wilson height (sopfr(nd))	4
Harmonic entropy (Shannon, [math]\displaystyle{ \sqrt{nd} }[/math])	~3.07644 bits
[sound info]
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English Wikipedia has an article on:

Fifteenth

4/1, the 4th harmonic, double octave, perfect fifteenth, tetrave or quadruple, is the harmonic past 3/1 and before 5/1. It is the first composite harmonic, equal to a stack of two octaves: (2/1)².

It can act as the interval of equivalence in temperaments that omit every other octave, such as meansquared.

See also

• Ed4 – equal divisions of the 4th harmonic