An appearance on Marian McPartland’s Piano Jazz radio broadcast often sheds light on unexplored aspects of an artist’s career as the host conducts her intrepid, conversational interviews. Here, we have both illuminating conversation and Shirley Horn’s musical essence: heartfelt ballad singing at crawling tempos, spot-on piano accompaniment, and deep-in-the-keys swing.

Unless she knew you well, Horn could be a reluctant conversationalist. In this setting, though, she sheds some light on her career and musical philosophy, saying that the “good music” her parents played at home (notably, Billie Holiday and Count Basie) deeply influenced her. At four, she started piano lessons, and as a teenager, she studied at Howard University. Horn also reflects fondly on a time in Washington, DC when she ran a jazz club, The Place Where Louis Dwells.

But it is the music that captivates. The most surprising moment comes at the start: a solo piano tour de force on “(Our) Love Is Here to Stay.” Horn plays in and around the insistent beat, although she never marks it in straight four. And, as is her wont, she reharmonizes the song to her own taste.

In their duets, host and guest alike swing, giggle, swagger and shout encouragement. They wend their way through three warhorses—”Cherry,” Charlie Parker’s “Billie’s Bounce” and Duke Ellington’s “Love You Madly”—as well as an improvised “Shirley’s Blues.” These rough-and-tumble outings are more jovial sparring than cutting contests; the pianists urge one another into abandon, bringing to mind earlier days when Horn would open her sets with a couple of long piano trio numbers. Here both pianists really dig into their blowing choruses. Elsewhere on the program, McPartland shines in her solo outings, Strayhorn’s “Blood Count” and a reflective “Guess I’ll Hang My Tears Out to Dry.”

The highlights of this broadcast, though, are Horn’s ballads. She offers sumptuous accompaniment to her “under-the-skin” vocals (quoting annotator Paul de Barros) on “I Could Have Told You,” “Violets for Your Furs” and “There’s No You.” Among the best of all her ballad performances, these pieces reveal understated yet palpable emotion, art without artifice.