There comes a moment during all the Charlie Parker Jazz Festivals I have seen in Marcus Garvey Park in Harlem when the crowd decides it is truly happy, and pockets of excitement form like chemical reactions onstage and in the audience. The crowd tends to be middle-aged or older — wise, skeptical, funny, good at staging an outburst.

It happened this summer at around 5:30 on Saturday afternoon during a set by the singer Rene Marie. We’d seen Erimaj, a changeable, still-evolving band led by the drummer Jamire Williams that crosses up about 40 years of pop and jazz in good ways. It can sound like Stevie Wonder’s 1970s band jamming on new-jazz harmonies with Spoon. (Its new album is “Conflict of a Man.”) And then the bassist Derrick Hodge, leading a band including the trumpeter Ambrose Akinmusire, playing tight virtuosic funk and gospel.

Ms. Marie has a smart, clear voice; she pushes her principles to the front of her work and playfully demands respect. Early on she sang “This for Joe,” defending the right to sing her own songs. But then she sang older songs, and when she and her band elaborated on “Them There Eyes,” the older couples began to come to the front and dance, interpreting the flow of the music. The energy settled around one particular pair of dancers, and every time they developed a new move, the crowd roared.

And so Roy Haynes, the drummer and bandleader, stepped before a softened, conditioned crowd. He wore a white satin suit with buttons up the legs from the ankle to the knee and performed a short tap dance before he began playing. He asked the audience if it knew how old he was; many, correctly, said 87. He made a show of denying it. At one point he played a solo with mallets, using wood on rims more than felt on drums, and suddenly stopped, seeming to encourage a response from the crowd, which he received. He looked pained. “Not now,” he hissed. “I’ll tell you when.” One minute later: “Now.”

“Y’all sound good,” he judged, sizing us up. “You look pretty good too.” He thought for a few seconds. “How do I look?”

Dedicated to Parker’s spirit if not always his music, the festival happens every year over the last weekend of August, one day in Harlem and another in Tompkins Square Park in the East Village. This year is the festival’s 20th, and extra panels, workshops and performances were added, including a third concert on Friday evening in Harlem, featuring the arranger Miguel Atwood-Ferguson’s new versions of pieces from the Parker album “Bird With Strings,” with Steve Wilson and Jaleel Shaw splitting Parker’s alto saxophone role. Mr. Shaw played in Mr. Haynes’s quartet on Saturday too, and he was a great presence: even toned but strong, relaxed but minutely refined in his control over rhythm.

Mr. Haynes, who first played with Parker in 1949, started with one of Thelonious Monk’s most fractured songs, “Trinkle, Tinkle,” and reduced his drumming to pure rhythm making: no pattern produced twice in a row on the ride cymbal, and no perceptible division between core beats and ornamental fills or flourishes. Everything was core and ornament at the same time.

“I want to see some of the slickest ladies up here,” he suggested, standing at the lip of the stage. Six rose up from the crowd and started aiming at him. “Look what I started,” he said. They swarmed him, kissing him, as he sang the O’Jays song “For the Love of Money.” He ordered someone to play a beat on the drums, and someone rushed forward from backstage to play the funk. One woman waggled her behind toward Mr. Haynes. “Give the drummer some,” he asked. She made a quarter turn and complied.

Various musicians who had played earlier that afternoon, or had come to hang out, stood and sat around the back wall of the stage, watching in amazement. I remembered something like that happening exactly nine years before to the day and probably the hour during a set by Mr. Haynes on the same stage.

Then he switched gears completely, and it took the audience only seconds to switch with him. He called for the standard “Autumn in New York,” one of the ballads Parker played best. Mr. Shaw played with just enough reserved emotion, making the song new, and his; Mr. Haynes toned down and concentrated, minimizing his sound, making it simple but graceful.