# Tenney height

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If n/d is a positive rational number reduced to its lowest terms, then the Benedetti height is the integer nd. Often it is more convenient instead to take the logarithm, usually base 2 (log2), of the Benedetti height, leading to Tenney height. In either form, it is widely used as a measure of inharmonicity and/or complexity for intervals. Alternative terms used include harmonic distance (HD).

## Names

In general mathematics, this measurement is known as log product complexity. With respect to microtonal tuning, this measurement was first described by James Tenney, who himself called it harmonic distance.[1][2][3] This terminology was also used in Paul Erlich's paper A Middle Path[4].

## Computation

### Ratio form

The Tenney height of a ratio n/d is given by

$\log_2 (nd)$

### Vector form

The Tenney height of a p-limit monzo b = [b1 b2bπ (p) (π being the prime-counting function) is given by

$\lVert H \vec b \rVert_1 \\ = \vert b_1 \vert + \vert b_2 \vert \log_2 (3) + \ldots + \vert b_{\pi (p)} \vert \log_2 (p) \\ = \log_2 (2^{|b_1|} \cdot 3^{|b_2|} \cdot \ldots \cdot p^{|b_{\pi (p)}|})$

where H is the transformation matrix such that, for the prime basis Q = 2 3 5 … p],

$H = \operatorname {diag} (\log_2 (Q))$

## Examples

Interval name Ratio (n/d) Monzo Tenney height
Unison 1/1 [0 0
Octave 2/1 [1 1
Just perfect fifth 3/2 [-1 1 2.585
Just major third 5/4 [-2 0 1 4.322
Harmonic seventh 7/4 [-2 0 0 1 4.807