Cents are based on the mathematical concept of logarithms. Logarithms were introduced by the Scottish mathematician John Napier (1550/4-1617). The name comes from *logos* (ratio) and *arithmós* (number). Logarithms are related to powers.

Two to the third power or \( 2^3 \) equals 1 x 2 x 2 x 2:

\( 2^3 = 1 * 2 * 2 * 2 = 8 \)

Two to the fourth power:

\( 2^4 = 1 * 2 * 2 * 2 * 2 = 16 \)

This is a tricky example that shows why we should start with 1:

\( 2^0 = 1 \) (1 multiplied by no 2)

The following figure illustrates the relationship between powers and logarithms:

Two, raised to the third power equals 8 ( \( 2 ^ 3 = 8 \) ). The logarithm indicates the power to which we must raise 2 to obtain 8. The second line reads: base 2 logarithm of 8 = 3. In other words, what power do we have to raise 2 (base 2) to get 8? The answer is 3.

In music we use base 2 logarithms because octaves inherently use this base. To find the frequency of a note an octave away, we need to multiply the frequency of the first note by two. Let us take C2 at 60 Hz. This gives us the frequency of C3:

\[ C3 = 60 * 2 = 120 \]

To get to C4, we multiply by 2, twice:

\[ C4 = 60 * 2 * 2 = 240 \]

Or we can use powers:

\[ C4 = 60 * 2^2 = 60 * 4 = 240 \]

The exponent used is related to the number of octaves:

Note |
Octaves |
Power |
Frequency |

\[ C2 \] | 0 | 0\[ 2^0 = 1 \] | 60 Hz. \[ 60 * 2^0 = 60 * 1 = 60 \] |

\[ C3 \] | +1 | 1\[ 2^1 = 2 \] | 120 Hz.\[ C3 = C2 * 2^1 = 60 * 2 = 120 \] |

\[ C4 \] | +2 | 2\[ 2^2 = 4 \] | 240 Hz.\[ C4 = C2 * 2^2 = 60 * 4 = 240 \] |

\[ C5 \] | +3 | 3\[ 2^3 = 8 \] | 480 Hz.\[ C5 = C2 * 2^3 = 60 * 8 = 480 \] |

Now let's use logarithms:

- Let's use the frequencies of C5 (480 Hz.) and C3 (120 Hz.). The notes are at two-octave distance.
- We divide the frequencies and the result is 4:

\( 480 / 120 = 4 \)

- What is the logarithm base 2 of 4, or what power must we raise 2 to get 4? The answer is 2, just as the number of octaves.

\( log_2(4) = 2 \)

- If we multiply C2's frequency \(2^2 \) we get C4's frequency:

\( 120 * 2^2 = 480 \)

We get the same result by *subtracting the powers*. The power needed to reach C5 from C2 is 3 (see the table above), that of C3 is 1. If we subtract 3 - 1, we get 2, the same result we obtained with \( log_2 (4) = 2 \).

Inadvertently, we are almost at Ellis' formula for calculating cents:

*We divide the note frequencies and find the base 2 logarithms of the result.*

There is only one small detail missing. We will see this in the next section.

It can all be confusing. It is like a labyrinth of mirrors in which it is easy to get lost. You have to go through it many times, with a lot of patience, and little by little you will find your way...

Let's summarize the mathematical concepts learned:

Powers: | \( \color{red}2 \color{blue}^3 \color{black}= 1 * 2 * 2 * 2 = \color{green}8 \) | Multiply 1 by 2 three times |
---|---|---|

Logarithms: | \( log\color{red}_2 \color{black} ( \color{green}8 \color{black} ) = \color{blue}3 \) | At what power should we raise 2 to get 8? |

If you can go from powers to logarithms and vice versa, you can consider the concept understood!

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Published by teoria.com.