organum ôr´gənəm [key], in music, compositional technique, developed in Europe during the 10th cent., in which each note of Gregorian chant melody was doubled by another note. In the earliest examples, called parallel organum, the doubling interval was constant, usually the lower fourth or fifth. In the 12th cent., composers began to apply a rapidly moving voice against the slow moving chant melody; the resulting compositions had two or more independent melodies and can be considered the beginning of polyphonic music.
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