Modulation (music) in the context of "Modern jazz"

In music, an arrangement is a musical adaptation of an existing composition. Differences from the original composition may include reharmonization, melodic paraphrasing, orchestration, or formal development. Arranging differs from orchestration in that the latter process is limited to the assignment of notes to instruments for performance by an orchestra, concert band, or other musical ensemble. Arranging "involves adding compositional techniques, such as new thematic material for introductions, transitions, or modulations, and endings. Arranging is the art of giving an existing melody musical variety". In jazz, a memorized (unwritten) arrangement of a new or pre-existing composition is known as a head arrangement.

Jazz improvisation is the spontaneous invention of melodic solo lines or accompaniment parts in a performance of jazz music. It is one of the defining elements of jazz. Improvisation is composing on the spot, when a singer or instrumentalist invents melodies and lines over a chord progression played by rhythm section instruments (piano, guitar, double bass) and accompanied by drums. Although blues, rock, and other genres use improvisation, it is done over relatively simple chord progressions which often remain in one key (or closely related keys using the circle of fifths, such as a song in C Major modulating to G Major).

Jazz improvisation is distinguished from this approach by chordal complexity, often with one or more chord changes per bar, altered chords, extended chords, tritone substitution, unusual chords (e.g., augmented chords), and extensive use of ii–V–I progression, all of which typically move through multiple keys within a single song. However, since the release of Kind of Blue by Miles Davis, jazz improvisation has come to include modal harmony and improvisation over static key centers, while the emergence of free jazz has led to a variety of types of improvisation, such as "free blowing", in which soloists improvise freely and ignore the chord changes.

Bebop or bop is a style of jazz developed in the early to mid-1940s in the United States. It is characterized by a fast tempo, complex chord progressions—with rapid chord changes, changes of key, and substitute chords—along with virtuosic improvisation based on a combination of harmonic structure, scales, and occasional references to the melody.

Bebop developed as the younger generation of jazz musicians expanded the creative possibilities of jazz beyond the popular, dance-oriented swing music-style to a new "musician's music" that was not as danceable and demanded close listening. As bebop was not intended for dancing, it enabled the musicians to play at faster tempos. Bebop musicians explored advanced harmonies, complex syncopation, altered chords, extended chords, chord substitutions, asymmetrical phrasing, and intricate melodies. Bebop groups used rhythm sections in a way that expanded their role. Whereas the key ensemble of the swing music era was the big band of 16–18 musicians playing in an ensemble-based style, the classic bebop group was a small combo that consisted of saxophone (alto or tenor), trumpet, piano, guitar, double bass, and drums playing music in which the ensemble played a supportive role for soloists. Rather than play heavily arranged music, bebop musicians typically played the melody of a composition (called the "head") with the accompaniment of the rhythm section, followed by a section in which each of the performers improvised a solo, then returned to the melody at the end of the composition.

A transition is a passage of music composed to link one section of music to another. Transitions often function as a moment of transformation and may, or may not in themselves, introduce new, musical material.

Often in music, the transition is the middle section or formal function, while the main theme is the beginning, and the subordinate theme is the ending. It may traditionally be a part of the sonata form's exposition in which the composer modulates from the key of the first subject to the key of the second, though many Classical era works move straight from first to second subject groups without any transition.

A borrowed chord (also called mode mixture, modal mixture, substituted chord, modal interchange, or mutation) is a chord borrowed from the parallel key (minor or major scale with the same tonic). Borrowed chords are typically used as "color chords", providing harmonic variety through contrasting scale forms, which are major scales and the three forms of minor scales. Chords may also be borrowed from other parallel modes besides the major and minor mode, for example D Dorian with D major. The mixing of the major and minor modes developed in the Baroque period.

Borrowed chords are distinguished from modulation by being brief enough that the tonic is not lost or displaced, and may be considered brief or transitory modulations and may be distinguished from secondary chords as well as altered chords. According to Sheila Romeo, "[t]he borrowed chord suggests the sound of its own mode without actually switching to that mode."

There is a long tradition in classical music of writing music in sets of pieces that cover all the major and minor keys of the chromatic scale. These sets typically consist of 24 pieces, one for each of the major and minor keys (sets that comprise all the enharmonic variants include 30 pieces).

Examples include Johann Sebastian Bach's The Well-Tempered Clavier and Frédéric Chopin's 24 Preludes, Op. 28. Such sets are often organized as preludes and fugues or designated as preludes or études. Some composers have restricted their sets to cover only the 12 major keys or the 12 minor keys; or only the flat keys (Franz Liszt's Transcendental Études) or the sharp keys (Sergei Lyapunov's Op. 11 set). In yet another type, a single piece may progressively modulate through a set of tonalities, as occurs in Ludwig van Beethoven's 2 Preludes through all the Major Keys, Op. 39.