Which medieval composer wrote a theory paper on the importance of new rhythms?

Philippe de Vitry

Explanation:

The medieval composer who wrote a theory paper on the importance of new rhythms was Philippe de Vitry. Philippe de Vitry was a music theorist, poet and composer who studied at the Sorbonne. He was also bishop of Meaux and a diplomat and adviser to Charles IV, Philip VI and John II. He is now mostly remembered for his treatise of music Ars Nova.

i think it was Philippe de Vitry