As a touring musician, Jennifer Hartswick knows what she likes. 

“Free concerts in the park are, like, my favorite thing,” the Trey Anastasio Band singer/trumpeter said from the Levitt Pavillon stage in Dayton, Ohio, where she and her tight-and-versatile band played a free concert in the park. 

“It’s like a lost art.”

For 80 minutes in 90-plus-degree temperatures and high humidity, music flowed from the quartet like an American river of soul, rock ’n’ roll, blues, funk and jazz on night felt “like winter” to the Tennessee resident. 

“This is beautiful,” Hartswick said of the weather, as a huge on-stage fan blew toward the musicians in the early evening of the late-summer day. 

Despite the cooling mechanism, Hartswick and guitarist Nick Cassarino struggled at times to keep their instruments in tune, though they and the rhythm section of Nate Edgar (bass) and Conor Elmes (drums) did not struggle in taking listeners on a sonic tour of American music. Hartswick is an engaging frontwoman, a powerful vocalist who holds notes for impossibly long periods and a horn section unto herself, but Cassarino is the on-stage energizer. He plays solos that match his animated stage presence, which riled up concertgoers all evening long.

So when Hartswick ceded the stage to him – “You can thank me later,” she said – to lead the band through B.B. King’s “How Blue Can You Get,” she also proved herself a generous and wise bandleader. As Hartswick looked on from beside the drums, Cassarino preceded to tear the Levitt to shreds, belting like an authentic bluesman and responding to his boss’ trumpet solo with a six-string ripper that found him stalking the front of the bandstand, getting on his tiptoes and generally taking control of the concert for 10 minutes.

“Remember when I said ‘You can thank me later?’ It’s later,” a beaming Hartswick said as many in the brown grass of the parched lawn stood and applauded the guitarist and band.

The balance of the show found Hartswick pulling songs from a master list and blending originals like the strutting “You Can’t Take it Back” and the funky “By the River,” which gave space for each instrumentalist to solo, with barn-busting covers such as Ray Charles’ “Drown in My Own Tears,” which made the sauna-like atmosphere of downtown Dayton that much more steamy.