How music works

Sound is a vibration travelling through the air as waves of pressure. The rate of vibration, its frequency, determines pitch: faster vibrations sound higher. The note A above middle C is commonly tuned to 440 vibrations per second.

When the frequency of a note doubles, we hear the same note an octave higher. This relationship feels so natural that musical traditions around the world treat notes an octave apart as versions of the same note.

A scale is a set of notes used to build melodies. Western music divides the octave into twelve equal steps called semitones, and the familiar major and minor scales use seven of them. Many other systems exist: Indian classical music uses ragas with subtle pitch inflections, and much folk music worldwide uses five-note pentatonic scales.

Timbre, or tone colour, is why a violin and a flute playing the same note sound different. Real instruments produce a fundamental frequency plus a series of fainter higher frequencies called overtones, and the mix of overtones gives each instrument its character.

The beat is the steady pulse you tap your foot to. Tempo is how fast that beat goes, measured in beats per minute. Beats are grouped into bars by a time signature: marches often count in twos or fours, while waltzes count in threes.

Rhythm is the pattern of long and short sounds laid over the beat. Syncopation, stressing notes that fall between the main beats, creates the forward-driving feel of jazz, funk and much Latin and African music. West African drumming traditions often layer several interlocking rhythms at once.

Melody is a sequence of notes heard one after another. Harmony is notes heard at the same time. Three or more notes sounding together form a chord, and the simplest chords, called triads, stack alternate notes of a scale.

Chords create tension and release. Some combinations sound stable and restful; others sound unresolved and pull toward a resolution. A great deal of popular music uses just a handful of chords in repeating patterns, while jazz and classical composers use richer harmonies and unexpected changes. Major keys often sound bright and minor keys darker, although culture strongly shapes how we hear them.

• Verse and chorus: the backbone of most popular songs, with changing verses and a repeated chorus.
• Twelve-bar blues: a set chord pattern that shaped jazz, rock and roll and much more.
• Theme and variations: a melody presented and then transformed in successive sections.
• Rondo: a main theme that keeps returning between contrasting sections.
• Symphony: a large orchestral work, usually in several movements with contrasting tempos and moods.

Researchers have found that listening to music we love can activate the brain's reward system, releasing dopamine, especially around moments of anticipated resolution or surprise. Music also synchronises groups of people, which may explain its central place in rituals, dances, protests and sports.

Every known human culture makes music, and bone flutes found in caves in Germany are over 40,000 years old. Whether music evolved for social bonding, courtship or as a by-product of language and hearing is still debated, but its universality suggests it is deeply rooted in human nature.