PEROTIN  

Pérotin was a successor of the composer Léonin in later 12th century Paris, active in his revision of the latters Magnus Liber and in the composition of organum, discant and conductus, as polyphonic practices in Western music developed.

Church Music

Examples of four-voice and three-voice organa by Pérotin survive, representing a significant advance in polyphonic technique. Organum, in its simplest form, consisted of the addition at first of a parallel part, at the distance of a fourth or fifth, to an original plainchant melody. By the 12th century the additional melodic lines were no mere parallel additions to the original but of greater rhythmic and melodic variety, based, as before, on the underlying original plainchant of the traditional Catholic liturgy.