Early in the documentary “Mixtape Trilogy: Stories of the Power of Music,” directed by Kathleen Ermitage, the composer and pianist Vijay Iyer, striving to describe the power of music, says, “I don’t want to say ‘magical,’ but I do.” This film, relatively modest in scale but broad in ambition, offers three stories of music makers and devotees.

It’s a mixed bag, alternating conventional homily with genuine, substantial analysis. Dylan Yellowlees’s adventures as an Indigo Girls superfan, which inspired not only her own coming out as gay, but led her to embrace activism, working for the National Center for Transgender Equality, are uplifting. Nevertheless, the section in which Amy Ray and Emily Sailers, of Indigo Girls, break down both the musical and verbal development of “Go,” Yellowlees’s favorite song of theirs, is meatier.

Next, the essayist and academic Garnette Cadogan and Iyer compare notes on their experience of racism. Iyer’s musings on the condition of being an American of South Asian descent working in the Black art form of jazz develop into a fascinating mini-disquisition on Iyer’s fascination with Detroit-based techno. It’s a music he feels is explicitly shaped for dancing in the face of oppression.

In these sequences, artist and admirer interact on camera; that’s not the case with the architect Michael Ford and the rapper Talib Kweli. But their discrete ideas about music building community are compassionate and, in Ford’s case, unique. His architectural designs are directly inspired by hip-hop lyrics, and he founded a children’s camp based on his ideas.

The music from the artists featured here is fine indeed, but the actual movie’s underscore, credited to an entity called “Scorebuzz,” is unmitigated treacle. As De Niro’s Jake LaMotta said in “Raging Bull,” “it defeats its own purpose.”

Mixtape Trilogy: Stories of the Power of Music
Not rated. Running time: 1 hour 33 minutes. Rent or buy on most major platforms.