Rhythm

• 1. Introduction

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  Rhythm comes from the Greek word rhythmos, meaning any regular recurring motion or symmetry. At its broadest, it describes a movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions. That single idea stretches across an astonishing range of time. The same word that names the riff in a rock song, lasting seconds, can also name cyclical natural phenomena that repeat over microseconds, or over minutes, hours, or even many years. So what holds together a heartbeat, a line of poetry, a building's row of windows, and the interlocking drums of West Africa? The answers reach back into human evolution, down into the limits of perception, and out across cultures that learned to count time in entirely different ways.

• 2. Rooted In Survival

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  Joseph Jordania suggested that the sense of rhythm developed in the early stages of hominid evolution through natural selection. Plenty of animals walk rhythmically and hear the heartbeat in the womb, yet only humans can be entrained into rhythmically coordinated vocalizations and shared activities. Jordania tied this to the battle trance, a specific neurological state he argued was crucial to the defense system of early hominids. The rhythmic war cry, the shaman's rhythmic drumming, the rhythmic drilling of soldiers, and combat forces listening to heavy rhythmic rock music all draw on one power. Rhythm can fuse separate individuals into a shared collective identity, where members place the group's interests above their own safety. Neurologist Oliver Sacks observed that some parrots can know rhythm, but chimpanzees and other animals show no similar appreciation of it. Sacks wrote that there is not a single report of an animal trained to tap, peck, or move in synchrony with an auditory beat. He acknowledged the objections of pet lovers and the Lipizzaner horses of the Spanish Riding School of Vienna, yet doubted whether such animals truly dance or merely respond to subtle visual or tactile cues from nearby humans. Sacks also held that the human affinity for rhythm is so fundamental it cannot be lost, even by stroke. Human rhythmic arts may be rooted, to some extent, in courtship ritual.

• 3. The Limits Of Perception

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  A continuous pulse cannot be heard as a musical beat if it runs faster than 8 to 10 per second or slower than one every 1.5 to 2 seconds. Too fast a beat becomes a drone. Too slow a succession of sounds seems unconnected. Musical tempo is generally specified between 40 and 240 beats per minute, a window that roughly matches the human heart rate and the duration of a single step or syllable. A pulse must also decay to silence before the next one arrives if it is to be truly distinct, because perceived loudness is relative to background noise. For this reason the fast-transient sounds of percussion instruments lend themselves to defining rhythm. Moravcsik arranged musical sound across five time scales of increasing duration. The supershort, a single cycle of an audible wave, is not heard as a separate event but as continuous pitch. The short is on the order of one second. The medium level, a few seconds or more, is where rhythm in music is actually defined, allowing a motif or figure to form. The long level spans many seconds or a minute and carries musical phrases. The very long covers minutes or hours and whole compositions. Curtis Roads took a wider view with nine time scales, reaching from microseconds in the sample domain up to natural periodicities of months, years, decades, and centuries that sit outside music entirely.

• 4. Strong And Weak

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  Rhythm may be defined as the way one or more unaccented beats are grouped in relation to an accented one. It always involves an interrelationship between a single strong beat and either one or two weak beats. This regulated succession of opposites runs through the dynamics of strong and weak, the played beat against the implied rest, and the long note against the short. Most music, dance, and oral poetry maintains an underlying metric level, a basic unit of time called the pulse or beat. The beat is not the fastest or slowest component but the one perceived as fundamental, the tempo to which listeners entrain as they tap a foot. In western notation it is most often a crotchet, or quarter note. Maury Yeston described rhythms of recurrence as arising from two levels of motion, the faster providing the pulse and the slower grouping the beats. Once a metric hierarchy is established, listeners maintain it as long as minimal evidence is present. The poetic term foot refers, as in dance, to the lifting and tapping of the foot in time, and musicians speak of upbeat and downbeat, on and off the beat. A rhythm that accents another beat and de-emphasises the expected downbeat is called syncopated. Even the most complex meters break down into chains of duple and triple pulses. According to Pierre Boulez, beat structures beyond four in western music are simply not natural.

• 5. When Rhythm Bends Tempo

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  Andranik Tangian used the leading rhythm of Promenade from Moussorgsky's Pictures at an Exhibition to show a strange difficulty. The same rhythm can be heard as it is, or as the first three events repeated at double tempo. Which reading wins depends on context, and Tangian explained this through the principle of correlative perception, where data are perceived in the simplest way. Drawing on Kolmogorov's complexity theory, simplest means the representation that minimizes the memory required. In his table, the rhythm without pitch needs 6 bytes when read as it is and 7 when read as a repeat, so the plain reading wins. Add a repeating melodic contour and the balance flips, because the redundancy makes the repeat the cheaper description. The more redundant the musical support of a pattern, the more robust its recognition under stretching or compressing, so distortions register as tempo changes rather than rhythmic ones. Skrjabin's own performance of his Poem op. 32 no. 1, transcribed from a piano-roll recording, contains tempo deviations spanning 5.5 times. Such freedom is strictly prohibited in Bulgarian and Turkish music built on additive rhythms with complex duration ratios. There, even a minor tempo deviation is not heard as accelerando or ritardando but as a change in rhythm, breaking the musical meaning.

• 6. Measured, Free, And None

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  Metrical or divisive rhythm, by far the most common in western music, calculates each time value as a multiple or fraction of the beat, with accents recurring regularly to form measures. Measured rhythm, also called additive rhythm, still measures values against a unit, but its accents do not recur regularly within the cycle. Free rhythm has neither, as in Christian chant, which keeps a basic pulse but flows more like prose than verse. Some music has no meter at all. Graphically scored works since the 1950s and the Honkyoku repertoire for shakuhachi may be considered ametric. The Italian term senza misura means without meter, playing without a beat and using time itself to measure how long a bar will take. Dance music sits at the opposite extreme, with instantly recognizable beat patterns built on a characteristic tempo and measure. The Imperial Society of Teachers of Dancing defines the tango as danced at approximately 66 beats per minute. Its basic slow step forward or backward lasts one beat and is called a slow, so a full right-left step equals one measure.

• 7. Carried By Voice

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  In the Griot tradition of Africa, everything related to music has been passed on orally. Babatunde Olatunji, who lived from 1927 to 2003, built a simple series of spoken sounds for teaching hand-drum rhythms. He used six vocal sounds, Goon, Doon, Go, Do, Pa, Ta, for three basic drum sounds, each struck with the left or right hand. John Miller argued that West African music is built on tension between rhythms, with one dominant rhythm interacting with independent competing rhythms that oppose or complement it. Moral values underpin a system based on repeating simple patterns that meet at distant cross-rhythmic intervals and on call-and-response form. Proverbs and lineages appear translated into drum talk or woven into song words, and audiences expect musicians to spark participation by reacting to dancers. Indian music has also travelled orally. Tabla players learn to speak complex rhythm patterns and phrases before attempting to play them. Sheila Chandra, an English pop singer of Indian descent, built performances around singing these patterns. In Indian classical music the Tala is the rhythmic pattern over which an entire piece is structured.

• 8. Breaking The Beat

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  In the 20th century, Igor Stravinsky, Bela Bartok, Philip Glass, and Steve Reich wrote rhythmically complex music using odd meters, phasing, and additive rhythm. Olivier Messiaen and his pupils pushed complexity further to disrupt any sense of a regular beat, a path that led to the irrational rhythms of New Complexity. John Cage noted why this matters. Regular rhythms cause sounds to be heard as a group rather than individually, so irregular rhythms let rapidly changing pitch relationships stand out instead of vanishing into rhythmic grouping. La Monte Young removed the beat another way, writing music made only of long sustained drones. In the 1930s, Henry Cowell wrote music with multiple simultaneous periodic rhythms and worked with Leon Theremin to invent the rhythmicon, the first electronic rhythm machine, to perform them. Conlon Nancarrow turned instead to the player piano. Rhythm also lives in speech, where isochrony is one of the three aspects of prosody alongside stress and intonation. Syllable-timed languages such as Spanish and Cantonese give roughly equal time to each syllable, while stress-timed languages such as English and Mandarin Chinese space stressed syllables evenly and squeeze the unstressed ones between them.