Chanticleer. (Wernher Krutein/Wernher Krutein)

Louis Botto founded the all-male choir Chanticleer in 1978 to perform music of the Middle Ages and early Renaissance. On Sunday, the current formation of the group closed out this year’s Georgetown Concert Series, which has presented two complete seasons at St. John’s Episcopal Church on O Street NW.

Chanticleer’s original mission was to sing music destined for a small consort of male voices, from countertenor to bass. In recent years, the San Francisco-based choir has focused more on arrangements of folk and popular songs, as well as mixed-choir repertory, music not originally meant for male ensemble. The membership, which numbers 12, includes three countertenors stretched, sometimes uncomfortably, into the soprano range. The group does not sing enough Renaissance music these days to be considered specialists, and its performance of 16th-century motets by Palestrina, Victoria and Guerrero mostly sounded rushed and unshaped. Intonation often did not lock into place except on final chords and, even then, not always.

Much of the rest of the program consisted of adaptations, beginning with “O frondens virga,” from Hildegard of Bingen’s “Ordo virtutum,” embellished with drones and a modern polyphonic refashioning of the final phrase. The group showed its most beautiful sound in Mendelssohn’s “Wasserfahrt,” because the piece was allowed to be slow and quiet, and because the composer intended it for men’s voices. Pieces for mixed voices could work, because of the admirable range of Chanticleer’s sopranos, but the Chanticleer sound, with a lot of forced loudness, often draws out their shrillness. That trademark wall of vocal tone was heard to excess in contemporary pieces by Stacy Garrop and Eric Whitacre and in effective arrangements of songs by Joni Mitchell and Ann Ronell.

Downey is a freelance writer.