# 4/3: Ratios

Next Page: 4/4 – Partials of Harmonic Series

## More on Ratios

Music is nothing but ratios and harmonic math, anyways.” ―Andrew Sega

The truest way to understand an interval or chord is with ratios. The numerator divided by the denominator generally ends up being between 1 and 2 (unison 1/1 to octave 2/1), to keep everything within the range of an octave. Each perfect fifth up is x3 for numerator (3, 9, 27, 81, etc. for each 5th) and the denominator is a multiple of 2 to bring the ratio into the octave (3/2, 9/8, 27/16, 81/64 etc.). Each perfect fifth down is 3x in the denominator (3, 9, 27, 81 etc.) and a multiple of 2 in the numerator, again to keep the ratio within the octave (4/3, 16/9, 32/27, 128/81). Each just third up is x5 in the numerator and a multiple of 2 in the denominator (5/4, 25/16, 125/64, etc.). Each just third down is x5 in the denominator and a multiple of 2 in the numerator (8/5, 32/25, 128/125, etc.). Each harmonic seventh up is x7 in the numerator and a multiple of 2 in the denominator (7/4, 49/48, etc.) and each seventh down is x7 in the denominator and a multiple of 2 in the numerator (8/7, 64/49, etc.).

To add two intervals, multiply their ratios and divide them down if necessary to bring them to within a single octave of each other (a fifth and a second is 3/2 x 9/8 = 27/16 or G + D = A; a fifth and a fourth is 3/2 x 4/3 = 12/6 or 2/1, G + F = C). To subtract one interval from another, invert the numerator and denominator of the interval being subtracted and multiply (a fifth minus a third is 3/2 – 5/4, or 3/2 x 4/5 = 12/10 or 6/5 E1b) If necessary, multiply or divide the numerator or denominator by 2 to get a ratio between 1 and 2, and divide both numerator and denominator together by whatever numbers possible to get the simplest number ratio (128/64 down to 2/1, for example).

A few of the most commonly used ratios appear in the Worldwide Musical Web, clustering around the starting note C, but there was no point in calculating ratios with numbers even bigger than the 2048/2025 of D2bb, for example.

This is a small and technical chapter of a much bigger book. If you would like to learn more about both Just Intonation and the 53-equal tuning system, you can buy the entire book, The Grand Unified Theory of Music, in pdf form for \$25 with hundreds of embedded musical examples of scales and chords from all over the world.

A free introduction to what The Grand Unified Theory of Music offers is on this website and includes both text and a few musical examples from each webpage. If you would like to learn more about this chapter and the full contents of this entire e-book, you can buy The Grand Unified Theory of Music for \$25, with hundreds of embedded musical examples of scales and chords from all over the world — and ideas for how to set up your computer system —

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You’ll get a personalized password you can use to see the entire e-book. Inside the full book, you will also get a link to the complete pdf file of this e-book, which you can read on your Kindle or similar device. The links to the hundreds of mp3 sound files – the same ones you can hear on the website — will also be included. This is “Version 1.0” of The Grand Unified Theory of Music. Because it is an e-book, additions, corrections and improvements in the sound may be added at any time. The Grand Unified Theory of Music is Copyright © 2018 by Christopher Mohr. All rights reserved.