This Is Your Brain on Music: The Science of a Human Obsession

Rhythm, tempo, and meter are closely related concepts associated with the duration of notes and the pace of a piece of music. Tempo describes how fast or slow a song is, generally referring to the beat, or “tactus,” which reflects how one would naturally tap their foot or snap their fingers along with a song. Tempo plays a big role in conveying emotions: Slow songs generally seem sadder, while fast songs typically come across as more upbeat and energetic. Tempo is processed in the cerebellum, and most people can recall tempo quite accurately, typically with only a 4% deviation from the original.

In songs, some beats are perceptually stronger, as though the musicians are playing them louder or heavier. These heavy beats distinguish the meter of the piece. In Western musical tradition, the standard duration of a note is four beats, and the most common pulse is a “quarter” note, which is a fourth of a whole note. The most common meter is therefore four quarter notes grouped together, written 4/4, with the strongest emphasis on the first quarter note in the group and the secondary emphasis on the third. The lyrics and melody of a song do not necessarily line up with its beat, often incorporating rests and cutting across beats for emotive effect. Other common meters in traditional Western music are the 3/4 meter (used in waltzes) and the 2/4 meter. All these meters have small integer ratios, which the human brain processes more easily than larger musical integer ratios, although other meters such as 5/4, 6/8, and 7/4 exist. Determining the meter of a piece of music can be difficult, and laypeople often conflate similar rhythms like 4/4 and 2/4.

Loudness is a fairly self-explanatory descriptor, except for the caveat that it is a purely psychological phenomenon resulting from the brain’s interpretation of auditory stimulus. Loudness is logarithmic, like pitch (rather than additive, like amplitude), and is measured in decibels (dB). A decibel is a ratio of sound levels that, like percentage, is dimensionless, but acousticians typically discuss sound levels in reference to a standard level of 20 micro pascals of sound pressure, approximately the lower threshold of hearing for most people. These units are referred to as dB (SPL), and prolonged exposure to approximately 120 dB (SPL) can cause permanent damage to the extremely sensitive human ear. Many people enjoy loud music, but even subtle changes in loudness can dramatically impact the mood of a piece.

Key and harmony govern expectations about pitch in music. Key is the tonal context of a tune, and while it can vary throughout a song, it necessarily lasts long enough to shape expectations. Keys are commonly used in Western music and are named for the central notes they gravitate toward. Harmony generally refers to countermelodies or chords played in conjunction with the main melody of a piece to affect its perceived pitch. Certain notes, when played in conjunction with other notes or chords, sound dissonant, while others sound consonant. Consonant harmonic intervals sound generally pleasing, while dissonant ones are more disquieting and even unpleasant. The combination of these features and the relationships between them characterize a song. Although the human brain processes separable elements of music immediately and individually, the brain also processes them collectively. The conscious mind plays some part in analyzing music, as is evident in the impact that experience and attention can have on processing. Although some areas of the brain have been mapped and associated with specific functions, many questions about the precise cognitive mechanisms by which the brain processes music remain unanswered.