Tone cluster in the context of Semitone

In Western music theory, a chord is a group of notes played together for their harmonic consonance or dissonance. The most basic type of chord is a triad, so called because it consists of three distinct notes: the root note along with intervals of a third and a fifth above the root note. Chords with more than three notes include added tone chords, extended chords and tone clusters, which are used in contemporary classical music, jazz, and other genres.

Chords are the building blocks of harmony and form the harmonic foundation of a piece of music. They provide the harmonic support and coloration that accompany melodies and contribute to the overall sound and mood of a musical composition. The factors, or component notes, of a chord are often sounded simultaneously but can instead be sounded consecutively, as in an arpeggio.

In music, extended chords are certain chords (built from thirds) or triads with notes extended, or added, beyond the seventh. Ninth, eleventh, and thirteenth chords are extended chords. The thirteenth is the farthest extension diatonically possible as, by that point, all seven tonal degrees are represented within the chord (the next extension, the fifteenth, is the same as the root of the chord). In practice however, extended chords do not typically use all the chord members; when it is not altered, the fifth is often omitted, as are notes between the seventh and the highest note (i.e., the ninth is often omitted in an eleventh chord; the ninth and eleventh are usually omitted in a thirteenth chord), unless they are altered to give a special texture.

Chords extended beyond the seventh are rarely seen in the Baroque era, and are used more frequently in the Classical era. The Romantic era saw greatly increased use of extended harmony. Extended harmony prior to the 20th century usually has dominant function – as V, V, and V, or V/V, V/ii etc.

Charles Edward Ives (/aɪvz/; October 20, 1874 – May 19, 1954) was an American modernist composer, actuary and businessman. Ives was among the earliest renowned American composers to achieve recognition on a global scale. His music was largely ignored during his early career, and many of his works went unperformed for many years. Later in life, the quality of his music was publicly recognized through the efforts of contemporaries like Henry Cowell and Lou Harrison, and he came to be regarded as an "American original". He was also among the first composers to engage in a systematic program of experimental music, with musical techniques including polytonality, polyrhythm, tone clusters, aleatory elements, and quarter tones. His experimentation foreshadowed many musical innovations that were later more widely adopted during the 20th century. Hence, he is often regarded as the leading American composer of art music of the 20th century.

Sources of Ives's tonal imagery included hymn tunes and traditional songs; he also incorporated melodies of the town band at holiday parade, the fiddlers at Saturday night dances, patriotic songs, sentimental parlor ballads, and the melodies of Stephen Foster.

Drone music (also known as drone-based music, or simply drone) is a minimalist genre of music that emphasizes the use of sustained sounds, notes, or tone clusters called drones. It is typically characterized by lengthy compositions featuring relatively slight harmonic variations. La Monte Young, one of its 1960s originators, defined it in 2000 as "the sustained tone branch of minimalism." Music containing drones can be found in many regional traditions across Asia, Australia, and Europe, but the genre label is generally reserved for music originating with the Western classical tradition. Elements of drone music have been incorporated in diverse genres such as rock, ambient, and electronic music.

In music or music theory, secundal is the quality of a chord made from seconds, and anything related to things constructed from seconds such as counterpoint. Secundal chords are often called tone clusters more generally, especially when non-diatonic. "[Any] three or more pitches in secundal relationship may correctly be referred to as a tone cluster." Chords which may be considered as built from sevenths, because of musical inversion, are secundal. Polychords may create secundal chords.

The secundal harmony in Ross Lee Finney's "Playing Tag" provides "accentuation and forward motion", as well as the basis for the "fragmentary melody":

Leo Ornstein (born Lev Ornshteyn; Russian: Лев Орнштейн; c. December 11, 1895 – February 24, 2002) was an American experimental composer and pianist of the early twentieth century. His performances of works by avant-garde composers and his own innovative and even shocking pieces made him a cause célèbre on both sides of the Atlantic. The bulk of his experimental works were written for piano.

Ornstein was the first important composer to make extensive use of the tone cluster. As a pianist, he was considered a world-class talent. By the mid-1920s, he had walked away from his fame and soon disappeared from popular memory. Though he gave his last public concert before the age of forty, he continued writing music for another half-century and beyond. Largely forgotten for decades, he was rediscovered in the mid-1970s. Ornstein completed his eighth and final piano sonata in September 1990 at the age of ninety-four, making him the oldest published composer in history at the time (a mark since passed by Elliott Carter).

The Tides of Manaunaun is a short piano piece in D♭ Major by American composer Henry Cowell (1897–1965). It premiered publicly in 1917, serving as a prelude to a theatrical production, The Building of Banba. The Tides of Manaunaun is the best known of Cowell's many tone cluster pieces.