Perotin

Succeeded Leonin at Notre Dame.  He developed organum from the Leonin style by instilling a greater rhythmic accuracy, and by making additions and modifications to the "Magnus Liber Organi".  His tenor voices were written in a series of rhythmic motives that were the precursors of the the rhythmic modes.  He expanded organum to three and four voices.  In addition, his music shows evidence of cannonic imitation.

Perotin was skilled in the art of discant, being described as "optimus discantor," while Leonin was called "optimus organista."