9/5

Interval information

Ratio	9/5
Factorization	32 × 5-1
Monzo	[0 2 -1⟩
Size in cents	1017.596¢
Names	just minor seventh, classic(al) minor seventh, ptolemaic minor seventh
Color name	g7, gu 7th
FJS name	[math]\displaystyle{ \text{m7}_{5} }[/math]
Special properties	reduced
Tenney height (log2 nd)	5.49185
Weil height (log2 max(n, d))	6.33985
Wilson height (sopfr(nd))	11
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Minor seventh

9/5, the just, classic(al), or ptolemaic minor seventh is often treated as a consonance in 5-limit just intonation, forming a part of such chords such as the 1-6/5-3/2-9/5 minor seventh chord, and the supermajor tetrad, 1-9/7-3/2-9/5 in the 7-limit.

Coincidentally, the ratio between a common "alternative" tuning frequency (A432) and the most common AC electrical frequency (60hz) is exactly 36/5, two octaves above 9/5. This is notably a more consonant interval than the 11/6 formed by the more common tuning frequency of A440, which may lead to a noticeable improvement in consonance when electrically powered instruments or amplifiers are interfered with by AC power.

See also

• 10/9 – its octave complement
• 5/3 – its twelfth complement
• Gallery of just intervals