Final answer:
The technique used by the Notre Dame School of Composers to embellish plainchant with multiple melodies creating a more complex polyphonic composition is known as counterpoint.
Step-by-step explanation:
The Notre Dame School of Composers innovated early Renaissance music by embellishing plainchant with multiple melodies, a technique called counterpoint. This development introduced more complex polyphonic compositions, contrasting the monophonic Gregorian chants of the Medieval era. Counterpoint allowed for the interweaving of independent melodic lines, enhancing the texture and harmony of the music.
Demand for music increased during the Renaissance, partly due to the invention of the Gutenberg press, which facilitated the distribution of music and theory. Renaissance music is characterized by modes, richer textures, blended musical strands, and an attention to chord progression. Employed extensively in sacred genres like masses and motets, as well as secular forms such as the madrigal, these advancements shaped the evolution of Western music.