What characterizes the organum style developed by early composers?

The organum style, which emerged during the medieval period as a prominent form of early polyphony, is characterized primarily by the addition of new vocal lines to existing Gregorian chants, which are monophonic. This practice involves taking a plainchant melody and adding a second voice that moves in parallel motion, often at a fixed interval, which enriches the texture and harmony of the original melody.

This style marked an important developmental stage in Western music, transitioning from solely monophonic textures to the beginnings of polyphony. The newly added vocal lines create a fuller sound while still retaining the essence of the original chant. Composers began experimenting with various intervals and counterpoint, laying the groundwork for more complex polyphonic techniques that would evolve in later periods.

While the other options touch upon elements related to music history, they do not accurately describe the essence of organum. Monophonic melodies only (the first option) do not capture the evolution represented by organum, which includes harmony and layering of voices. The invention of contrapuntal techniques highlighted in the second option refers to a broader development in music and is more characteristic of later compositions rather than the foundational practices of early organum. Finally, the focus on instrumental music in the last option does not