What is a collection of art songs, unified by poet, narrative, musical style, or composer?

I believe the correct answer is: song cycle.

The collection of art songs, unified by poet, narrative, musical style, or composer are called song cycle or program music for instrumental music associated with story, poem, idea, or scene. First song cycle was “Il Canzoniere” or “Rime Sparse” written by Italian humanist poet Francesco Petrarca to his belove Laura.

pitch- the definition of pitch is as follows:

"the quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone."