Cycle has several meanings in the field of music. Acoustically, it refers to one complete vibration, the base unit of Hertz being one cycle per second. Theoretically, an interval cycle is a collection of pitch classes created by a sequence of identical intervals. Individual pieces that aggregate into larger works are considered cycles, for example, the movements of a suite, symphony, sonata, or string quartet. This definition can apply to everything from settings of the Mass or a song cycle to an opera cycle. Cycle also applies to the complete performance of an individual composer's work in one genre.
Harmonic cycles--repeated sequences of a harmonic progression--are at the root of many musical genres, such as the twelve-bar blues. In compositions of this genre, the chord progression may be repeated indefinitely, with melodic and lyrical variation forming the musical interest. The form theme and variations is essentially of this type, but generally on a larger scale.
Composition using a tone row is another example of a cycle of pitch material, although it may be more difficult to hear because the variations are more diverse.
In the gamelan music of Indonesia, there are nested gong cycles which determine the rhythmic framework of the piece. This sort of cycling is called colotomy. In the same way as specific harmonic cycles determine the genre of many Western pieces (like the blues), gamelan pieces are classified according to their colotomic structures. Some other styles of music, such as gagaku or pi phat, have been analyzed colotomically.
Rhythm in Sub-Saharan Africa is typically generated by multiple cross-rhythmic cycles, in relation to a primary cycle of four main beats. This basic musical period has a bipartite structure; it is made up of two rhythmically opposed cells, consisting of two beats each. Kubik points out that the four-beat cycle is a shorter period than what is normally heard in European music. This accounts for the stereotype of African music as "repetitive." The cycles have a beginning and an end, with the two joining. The lead instrument, or soloist, may temporarily contradict the primary cycle with cross beats and larger phrases, but awareness of the cycle is ever present. In many sub-Saharan and Disapora musics, a key pattern, typically played on a bell, establishes the basic cycle or period.
Different types of musical cycles can overlap. One example is isorhythm, the medieval practice of using melodic and rhythmic cycles in one or two voices. There is a certain sequence of pitch material (known as the color) and a separate sequence of rhythmic values (known as the talea), which is of different length. If the lengths of the two cycles are relatively prime, a complex melody will emerge. Most compositions using this technique end when the two cycles coincide.
A similar process is used in serial music, although the number of different overlapping cycles can be quite large, and encode a wide variety of musical parameters, such as dynamics, articulation, timbre, register, and so forth.