Cycle has several meaning in the field of music. Acoustically, it refers to one complete vibration, the base unit of Hertz being one cycle per second.[1] 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. 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.[2]
A cycle can also mean a section which is repeated or repeatable indefinitely, with the end of a preceding repetition leading to the beginning of a succeeding repetition. Cycles may be melodic, harmonic, rhythmic, or based on some other musical dimension. Cycles may begin at any point in a composition or in relation to another cycle, contain or consist of cycles, and may be varied upon repetition.
Harmonic cycles 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.
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The music of both India and Indonesia are noted for their cyclical approach to rhythms. In Indian classical music, a specific rhythmic structure known as a tala is repeated through the length of the raga, and used as a basis for improvisation of the drum parts.
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.
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.