Rhythm





Rhythm (from Greek ῥυθμός – rhythmos, "any regular recurring motion, symmetry" ) may be generally defined as a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions." This general meaning of regular recurrence or pattern in time may be applied to a wide variety of cyclical natural phenomena having a periodicity or frequency of anything from microseconds to millions of years. In the performance arts rhythm is the timing of events on a human scale; of musical sounds and silences, of the steps of a dance, or the metre of spoken language and poetry. Rhythm may also refer to visual presentation, as "timed movement through space." and a common language of pattern unites rhythm with geometry. 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.

Anthropology
In his series How Music Works, Howard Goodall presents theories that human rhythm recalls the regularity with which we walk and the heartbeat we heard in the womb. London writes that musical metre "involves our initial perception as well as subsequent anticipation of a series of beats that we abstract from the rhythm surface of the music as it unfolds in time" (London 2004, 4). The "perception" and "abstraction" of rhythmic measure is the foundation of human instinctive musical participation, as when we divide a series of identical clock-ticks into "tick-tock-tick-tock". Neurologist Oliver Sacks states that chimpanzees and other animals show no similar appreciation of rhythm yet posits that human affinity for rhythm is fundamental, so that a person's sense of rhythm cannot be lost (e.g. by stroke). Human rhythmic arts are possibly to some extent rooted in courtship ritual. The establishment of a basic beat requires the perception of a regular sequence of distinct short-duration pulses and, as subjective perception of loudness is relative to background noise levels, a pulse must decay to silence before the next occurs if it is to be really distinct. For this reason the fast-transient sounds of percussion instruments lend themselves to the definition of rhythm. Musical cultures that rely upon such instruments may develop multi-layered polyrhythm and simultaneous rhythms in more than one time signature, called polymeter. Such are the cross-rhythms of Sub-Saharan Africa and the interlocking kotekan  rhythms of the Indonesian gamelan. For information on rhythm in Indian music see Tala (music). For other Asian approaches to rhythm see Rhythm in Persian music, Rhythm in Arabian music and Usul - Rhythm in Turkish music and Dumbek rhythms.

Pulse, beat and measure
(See main articles; Pulse (music), Beat (music)) Most music, dance and oral poetry establishes and maintains an underlying "metric level", a basic unit of time that may be audible or implied, the pulse or tactus of the mensural level, or beat level,  sometimes simply called the beat. This consists of a (repeating) series of identical yet distinct periodic short-duration stimuli perceived as points in time. The "beat" pulse is not necessarily the fastest or the slowest component of the rhythm but the one that is perceived as basic: it has a tempo to which listeners entrain as they tap their foot or dance to a piece of music (Handel, 1989). It is currently most often designated as a crotchet or quarter note in western notation (see time signature). Faster levels are division levels, and slower levels are multiple levels (Wittlich 1975, chapt. 3). "Rhythms of recurrence" arise from the interaction of two levels of motion, the faster providing the pulse and the slower organizing the beats into repetitive groups (Yeston 1976, 50–52). "Once a metric hierarchy has been established, we, as listeners, will maintain that organization as long as minimal evidence is present" (Lester 1986, 77).

Unit and gesture
A durational pattern that synchronises with a pulse or pulses on the underlying metric level may be called a rhythmic unit. These may be classified as; metric - even patterns, such as steady eighth notes or pulses - intrametric - confirming patterns, such as dotted eighth-sixteenth note and swing patterns - contrametric - non-confirming, or syncopated patterns and extrametric - irregular patterns, such as tuplets. A rhythmic gesture is any durational pattern that, in contrast to the rhythmic unit, does not occupy a period of time equivalent to a pulse or pulses on an underlying metric level. It may be described according to its beginning and ending or by the rhythmic units it contains. Beginnings on a strong pulse are thetic, a weak pulse, anacrustic and those beginning after a rest or tied-over note are called initial rest. Endings on a strong pulse are strong, a weak pulse, weak and those that end on a strong or weak upbeat are upbeat.

Alternation and repetition
Rhythm is marked by the regulated succession of opposite elements, the dynamics of the strong and weak beat, the played beat and the inaudible but implied rest beat, the long and short note. As well as perceiving rhythm we must be able to anticipate it. This depends upon repetition of a pattern that is short enough to memorize. The alternation of the strong and weak beat is fundamental to the ancient language of poetry, dance and music. The common poetic term "foot" refers, as in dance, to the lifting and tapping of the foot in time. In a similar way musicians speak of an upbeat and a downbeat and of the "on" and "off" beat. These contrasts naturally facilitate a dual hierarchy of rhythm and depend upon repeating patterns of duration, accent and rest forming a "pulse-group" that corresponds to the poetic foot. Normally such pulse-groups are defined by taking the most accented beat as the first and counting the pulses until the next accent (MacPherson 1930, 5; Scholes 1977). A rhythm that accents another beat and de-emphasises the down beat as established or assumed from the melody or from a preceding rhythm is called syncopated rhythm. Normally, even the most complex of meters may be broken down into a chain of duple and triple pulses (MacPherson 1930, 5; Scholes 1977) either by addition or division. According to Pierre Boulez, beat structures beyond four are "simply not natural". Western rhythms are usually arranged with respect to a time signature, partially signifying a meter usually corresponding to measure length and grouped into either two or three beats, which are called duple meter and triple meter, respectively. If the beats are in consistently even or odd groups of two, three, or four, it is simple meter, if by admixtures of two and three it is compound meter.

Tempo and duration
(See main articles; Duration (music), Tempo) The tempo of the piece is the speed or frequency of the tactus, a measure of how quickly the beat flows. This is often measured in 'beats per minute' (bpm): 60 bpm means a speed of one beat per second, a frequency of 1Hz. A rhythmic unit is a durational pattern that has a period equivalent to a pulse or several pulses. The duration of any such unit is inversely related to its tempo. Musical sound may be analyzed on five different time scales, which Moravscik has arranged in order of increasing duration; : Curtis Roads takes a wider view by distinguishing nine time scales, this time in order of decreasing duration. The first two, the infinite and the supramusical, encompass natural periodicities of months, years, decades centuries and greater, while the last three, the sample and subsample, which take account of digital and electronic rates "too brief to properly recorded or perceived", measured in millionths microseconds, and finally the infinitesimal or infinitely brief, are again in the extra-musical domain. Roads' Macro level, encompassing "overall musical architecture or form" roughly corresponds to Moravcsik's "very long" division while his Meso level, the level of "divisions of form" including movements, sections, phrases taking seconds or minutes, is likewise similar to Moravcsik's "long" category. Roads' Sound object (Schaeffer 1959, 1977): "a basic unit of musical structure" and a generalization of note (Xenakis' ministructural time scale); fraction of a second to several seconds, and his Microsound (see granular synthesis) down to the threshold of audible perception; thousands to millionths of seconds, are similarly comparable to Moravcsik's "short" and "supershort" levels of duration.
 * Supershort: a single cycle of an audible wave, approximately 1/30-1/10,000 second (30-10,000 Hz or more than 1,800 bpm). These, though rhythmic in nature, are not perceived as separate events but as continuous musical pitch.
 * Short: of the order of one second (1 Hz, 60bpm, 10-100,000 audio cycles). Musical tempo is generally specified in the range 40 to 240 beats per minute. A continuous pulse cannot be perceived as a musical beat if it is faster than 8-10 per second (8-10 Hz, 480-600 bpm) or slower than 1 per 1.5 – 2 seconds (0.6-0.5 Hz, 40-30 bpm). Too fast a beat becomes a drone, too slow a succession of sounds seems unconnected. This time-frame roughly corresponds to the human heart rate and to the duration of a single step, syllable or rhythmic gesture.
 * Medium: ≥ few seconds, This median durational level "defines rhythm in music" as it allows the definition of a rhythmic unit, the arrangement of an entire sequence of accented, unaccented and silent or "rest" pulses into the cells of a measure that may give rise to the "briefest intelligible and self-existent musical unit", a motif or figure. This may be further organized, by repetition and variation, into a definite phrase that may characterise an entire genre of music, dance or poetry and that may be regarded as the fundamental formal unit of music.
 * Long: ≥ many seconds or a minute, corresponding to a durational unit that "consists of musical phrases" which may make up a melody, a formal section, a poetic stanza or a characteristic sequence of dance moves and steps. Thus the temporal regularity of musical organisation includes the most elementary levels of musical form
 * Very long: ≥ minutes or many hours, musical compositions or subdivisions of compositions.

Metric structure
(See main articles; Metre (music), Measure (music), Metre (poetry)) The study of rhythm, stress, and pitch in speech is called prosody: it is a topic in linguistics and poetics, where it means the number of lines in a verse, the number of syllables in each line and the arrangement of those syllables as long or short, accented or unaccented. Music inherited the term "meter or metre" from the terminology of poetry. The metric structure of music includes meter, tempo and all other rhythmic aspects that produce temporal regularity against which the foreground details or durational patterns of the music are projected (Wittlich 1975, chapt. 3). The terminology of western music is notoriously imprecise in this area (Scholes 1977). MacPherson (1930, 3) preferred to speak of "time" and "rhythmic shape", Imogen Holst (1963, 17) of "measured rhythm". Dance music has instantly recognizable patterns of beats built upon a characteristic tempo and measure. The Imperial Society of Teachers of Dancing (1983) defines the tango, for example, as to be danced in 2/4 time at approximately 66 beats per minute. The basic slow step forwards or backwards, lasting for one beat, is called a "slow", so that a full "right-left" step is equal to one 2/4 measure. The general classifications of metrical rhythm, measured rhythm, and free rhythm may be distinguished. Metrical or divisive rhythm, by far the most common in Western music calculates each time value as a multiple or fraction of the beat. Normal accents re-occur regularly providing systematical grouping (measures). Measured rhythm (additive rhythm)also calculates each time value is a multiple or fraction of a specified time unit but the accents do not recur regularly within the cycle. Free rhythm is where there is neither (Cooper 1973, 30), such as in Christian chant, which has a basic pulse but a freer rhythm, like the rhythm of prose compared to that of verse (Scholes 1977) See Free time (music). Finally some music, such as some graphically scored works since the 1950s and non-European music such as Honkyoku repertoire for shakuhachi, may be considered ametric (Karpinski 2000, 19). Senza misura is an Italian musical term for "without meter", meaning to play without a beat, using time to measure how long it will take to play the bar (Forney and Machlis 2007, ).

Composite rhythm
A composite rhythm is the durations and patterns (rhythm) produced by amalgamating all sounding parts of a musical texture. In music of the common practice period, the composite rhythm usually confirms the meter, often in metric or even-note patterns identical to the pulse on a specific metric level.

Rhythm in linguistics
Narmour 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.

Rhythm notation
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 (1927–2003), a Nigerian drummer who lived and worked in the United States, developed a simple series of spoken sounds for teaching the rhythms of the hand drum. He used six vocal sounds: Goon Doon Go Do Pa Ta. There are three basic sounds on the drum, but each can be played with either the left or the right hand. This simple system is now used worldwide, particularly by Djembe players. It is noteworthy that the debate about the appropriateness of staff notation for African music is a subject of particular interest to outsiders, not insiders. African scholars from Kyagambiddwa to Kongo have for the most part accepted the conventions—and limitations—of staff notation and gone on to produce transcriptions in order to inform and to make possible a higher level of discussion and debate.— Agawu (2003: 52) John Miller Chernoff 1979 has argued that West African music is based on tension between rhythms. A set of moral values underpins a full musical system based on repetition of relatively simple patterns which meet at distant intervals and call and answer schemes. Values also show up in collective utterances such as proverbs or lineages appear either in phrases that translate as drum talk or in the words of songs. People expect musicians to stimulate participation of all present, notably by reacting to people dancing the music. Appreciation of musicians is related to the effectiveness of their upholding community values.

Indian music
Indian music has also been passed on orally. 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, made performances based on her singing these patterns. In Indian Classical music, the Tala of a composition is the rhythmic pattern over which the whole piece is structured.

Western music
In the 20th century, composers like Igor Stravinsky, Béla Bartók, 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. 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 Thérémin to invent the Rhythmicon, the first electronic rhythm machine, in order to perform them. Similarly, Conlon Nancarrow wrote for the player piano.