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Music and mathematics

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Music and mathematics are deeply linked through patterns and numerical relationships. Music theory analyzes elements like pitch, timing, and structure. It uses math to study tempo, chord progression, and meter. While music theory lacks a purely axiomatic foundation in modern mathematics, the basis of sound is mathematical. This field is known as musical acoustics.

Spectrogram of violin
Spectrogram of violin

Sound exhibits a remarkable array of number properties that define how we hear. Composers even use advanced math like set theory and abstract algebra to create new ways of hearing music.

History shows that humans have noticed these connections for thousands of years. Ancient Chinese, Indian, Egyptian, and Mesopotamian cultures studied the mathematical principles of sound. In ancient Greece, the Pythagoreans were the first to investigate musical scales using numerical ratios. They specifically looked at ratios of small integers. They believed that all nature consists of harmony arising from numbers.

HarmonicIdentities.Names.Frequencies
HarmonicIdentities.Names.Frequencies

Even the philosopher Confucius viewed the small numbers 1, 2, 3, and 4 as sources of perfection.

Time and rhythm provide the necessary boundaries for music. Without rhythmic structure, music would not be possible. This structure involves a regular arrangement of pulse, accent, and duration. The modern use of terms like meter and measure reflects how music helped develop arithmetic. It also helped develop the exact measurement of time and periodicity.

Chladini.Diagrams.for.Quadratic.Plates
Chladini.Diagrams.for.Quadratic.Plates

Musical form acts as a plan for extending a short piece of music. This is similar to how an architect uses a plan for a building. Composers use repetition and order to create these structures. Some forms use strict proportions based on powers of 2 and 3.

Every musical pitch corresponds to a specific frequency. We measure this in hertz (Hz), which means cycles per second.

Middle C, or 262 hertz, on a virtual oscilloscope
Middle C, or 262 hertz, on a virtual oscilloscope

A musical scale is a set of these pitches. The most important scale in the Western tradition is the diatonic scale. A key feature of scales is the interval of repetition called the octave. An octave occurs when a frequency is exactly twice that of a starting pitch.

C5 523 Hz oscillogram
C5 523 Hz oscillogram

Higher pitches at twice the frequency are called superoctaves. These include frequencies four, eight, or sixteen times the fundamental. Pitches at half or a quarter frequency are called suboctaves.

C3 131 Hz oscillogram
C3 131 Hz oscillogram

Because octaves grow by doubling, they follow an exponential pattern. For example, an octave from A2 to A3 spans 110 Hz to 220 Hz. The next octave spans 220 Hz to 440 Hz. Each successive octave spans twice the frequency range of the one before it.

4Octaves.and.Frequencies
4Octaves.and.Frequencies

Because we focus on the ratios between pitches, we often call these intervals. We can also use cents to compare the size of these intervals. This mathematical relationship ensures that octaves always sound like the same note name.

There are two main families of tuning systems: equal temperament and just tuning. Equal temperament divides an octave into intervals that are equal on a logarithmic scale. This creates perfectly even scales, but the frequency ratios are irrational numbers.

4Octaves.and.Frequencies.Ears
4Octaves.and.Frequencies.Ears

Just tuning uses rational numbers to create simple frequency ratios. This results in uneven scale divisions but produces different acoustical results. A major difference is the presence of "beats" when notes are played together. This affects whether a sound feels consonant or dissonant to the listener.

Just intonation, specifically 5-limit tuning, uses regular number harmonics. Johannes Kepler presented such scales in his 1619 work, *Harmonices Mundi*. He connected these scales to planetary motion. In just tuning, you find a note's frequency by multiplying the tonic by a ratio. For example, a justly tuned fifth above A4 (440 Hz) is 660 Hz. This is calculated as 440 multiplied by the ratio 3:2. While just tuning sounds very pure, fixed instruments like pianos cannot easily change keys using it.

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🖼️ Images & Media (9)
File:Spectrogram of violin.png
Spectrogram of violin.png
File:Chladini.Diagrams.for.Quadratic.Plates.svg
Chladini.Diagrams.for.Quadratic.Plates.svg
File:4Octaves.and.Frequencies.svg
4Octaves.and.Frequencies.svg
File:4Octaves.and.Frequencies.Ears.svg
4Octaves.and.Frequencies.Ears.svg
File:Middle_C,_or_262_hertz,_on_a_virtual_oscilloscope.png
Middle_C,_or_262_hertz,_on_a_virtual_oscil...
File:C5_523_Hz_oscillogram.png
C5_523_Hz_oscillogram.png
File:C3_131_Hz_oscillogram.png
C3_131_Hz_oscillogram.png
File:HarmonicIdentities.Names.Frequencies.svg
HarmonicIdentities.Names.Frequencies.svg
File:Normalized harmonic identities, names, and frequencies.svg
Normalized harmonic identities, names,...
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