Chapter II

Physical-Acoustic Foundations of Musical Matter

The wave nature of sound, the harmonic series and equal temperament

3.1 The Wave Nature of Sound: Frequency, Amplitude and Timbre

From a strictly physical standpoint, sound is a longitudinal mechanical wave that propagates through an elastic medium by successive cycles of molecular compression and rarefaction. Three fundamental parameters define the identity of any musical sound:

• Frequency (Pitch): Determines whether a sound is low or high, measured in Hertz (Hz).
• Amplitude (Intensity): Relates to the volume or strength of the sound, measured in decibels (dB).
• Timbre: The tone colour that lets us tell a guitar from a piano even when they play the same note.

3.2 The Harmonic Series and the Physical Justification of Consonance

When a guitar string or the strings of a piano are struck, they do not vibrate only as a whole. The string divides simultaneously into geometric fractions (half, thirds, quarters, fifths, and so on), generating secondary frequencies that resonate together with the fundamental frequency.