Rhythm

Rhythm (Greek  = 'flow', or in Modern Greek, 'style') is the variation of the length and accentuation of a series of sounds or other events. "Rhythm involves patterns of duration that are phenomenally present in the music" with duration perceived by interonset interval (London 2004, p.4). When governed by rule, it is called meter. It is inherent in any time-dependent medium, but it is most associated with music, dance, and the majority of poetry.

Rhythm in linguistics
The study of rhythm, stress, and pitch in speech is called prosody; it is a topic in linguistics. Narmour (1980, p.147-53) describes three categories of prosodic rules which create rhythmic successions which are additive (same duration repeated), cumulative (short-long), or countercumulative (long-short). Cumulation is associated with closure or relaxation, countercumulation with openness or tension, while additive rhythms are open-ended and repetitive. Richard Middleton points out this method cannot account for syncopation and suggests the concept of transformation.

A rhythmic unit is a durational pattern which occupies a period of time equivalent to a pulse or pulses on an underlying metric level, as opposed to a rhythmic gesture which does not (DeLone et. al. (Eds.), 1975, chap. 3).

Rhythm in music
All musicians, instrumentalists and vocalists, work with rhythm, but in modern music a rhythm section generally consists of percussion instruments, bass and possibly chordal instruments (e.g., guitar, banjo) and keyboard instruments, such as piano. In recent years, music theorists have attempted to explain connections between rhythm, meter, and the broad structure and organization of sound events in music. Some have suggested that rhythm (and its essential relationship to the temporal aspect of sound) may in fact be the most fundamental aspect of music. Hasty (1997, p. 3), for example, notes that "Among the attributes of rhythm we might include continuity or flow, articulation, regularity, proportion, repetition, pattern, alluring form or shape, expressive gesture, animation, and motion (or at least the semblance of motion). Indeed, so intimate is the connection of the rhythmic and the musical, we could perhaps most concisely and ecumenically define music as the 'rhythmization' of sound."

Origins of human appreciation of rhythm
In his series How Music Works, Howard Goodall presents theories that rhythm recalls how we walk and the heartbeat we heard in the womb. However neither would seem to have any survival value in Man's evolution. More likely is that a simple pulse or di-dah beat recalls the footsteps of another person. Our sympathetic urge to dance is designed to boost our energy levels in order to cope with someone (or some animal) chasing us -- a fight or flight response.

Rhythm Notation and the Oral Tradition
Worldwide there are many different approaches to passing on rhythmic phrases and patterns, as they exist in traditional music, from generation to generation.

African music
In the Griot tradition of Africa everything related to music has been passed on orally. Babatunde Olatunji, A Nigerian Drummer living and working in the USA developed a simple series of spoken sounds for teaching the rhythms of the hand drum. He used six vocal sounds: Goon Doon Go Do Ga Da. There are three basic sounds on the drum but each can be played with left or right hand. This simple system is now used worldwide particularly by Djembe players.

Indian music
Again an oral tradition. Tabla players would learn to speak complex rhythm patterns and phrases before attempting to play them. Sheila Chandra an English pop singer of Indian descent created performances based around her singing these patterns. In Indian Classical music the Tala of a composition is basically the rhythmic pattern over which the whole piece is structured.

Western music
Standard Music notation contains all rhythmic information and is adapted specifically for drums and percussion instruments.

Types
In Western music, rhythms are usually arranged with respect to a time signature, partially signifying a meter. The speed of the underlying pulse, called the beat, is the tempo. The tempo is usually measured in 'beats per minute' (bpm); 60 bpm means a speed of one beat per second. The length of the meter, or metric unit (usually corresponding with measure length), is usually grouped into either two or three beats, being called duple meter and triple meter, respectively. If each beat is grouped in two, it is simple meter, if in three compound meter.

Syncopated rhythms are rhythms that accent parts of the beat not already stressed by counting. Playing simultaneous rhythms in more than one time signature is called polymeter. See also polyrhythm. In recent years, rhythm and meter have become an important area of research among music scholars. Recent work in these areas includes books by Maury Yeston, Fred Lerdahl and Ray Jackendoff, Jonathan Kramer, Christopher Hasty, William Rothstein, and Joel Lester.

Some genres of music make different use of rhythm than others. Most Western music is based on divisive rhythm, while non-Western music uses more additive rhythm. African music makes heavy use of polyrhythms, and Indian music uses complex cycles such as 7 and 13, while Balinese music often uses complex interlocking rhythms. By comparison, a lot of Western classical music is fairly rhythmically simple; it stays in a simple meter such as 4/4 or 3/4 and makes little use of syncopation. Clave is a common underlying rhythm in African, Cuban music, and Brazilian music.

In the 20th century, composers like Igor Stravinsky, Philip Glass, and Steve Reich wrote more rhythmically complex music using odd meters, and techniques such as phasing and additive rhythm. At the same time, modernists such as Olivier Messiaen and his pupils used increased complexity to disrupt the sense of a regular beat, leading eventually to the widespread use of irrational rhythms in New Complexity. This use may be explained by a comment of John Cage's where he notes that regular rhythms cause sounds to be heard as a group rather than individually; the irregular rhythms highlight the rapidly changing pitch relationships that would otherwise be subsumed into irrelevant rhythmic groupings (Sandow 2004, p.257). LaMonte Young also wrote music in which the sense of a regular beat is absent because the music consists only of long sustained tones (drones). In the 1930s, Henry Cowell wrote music involving multiple simultaneous periodic rhythms and collaborated with Léon Theremin to invent the Rhythmicon, the first electronic rhythm machine, in order to perform them. Similarly, Conlon Nancarrow wrote for player piano.