Quarter tone in the context of Gérard Grisey

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.

In the musical system of ancient Greece, an octave species (Greek: εἶδος τοῦ διὰ πασῶν, or σχῆμα τοῦ διὰ πασῶν) is a specific sequence of intervals within an octave. In Elementa harmonica, Aristoxenus classifies the species as three different genera, distinguished from each other by the largest intervals in each sequence: the diatonic, chromatic, and enharmonic genera, whose largest intervals are, respectively, a whole tone, a minor third, and a ditone; quarter tones and semitones complete the tetrachords.

The concept of octave species is very close to tonoi and akin to musical scale and mode, and was invoked in Medieval and Renaissance theory of Gregorian mode and Byzantine Octoechos.

In music theory, a neutral interval in 24 TET (including extensions), (but also known as a submajor interval, or as a superminor interval, in Just Intonation), is an interval that is neither major nor minor, but is, instead, in-between them.

In 12 TET, these intervals are a quarter tone sharper than minor intervals and a quarter tone flatter than major intervals. For example, the minor third is tuned at 300 ¢, while the major third is a semitone (100 ¢) sharper (400 ¢), and so the neutral third lies between them at 350 ¢.