All these years later, we’re still talking about Woodstock. But what about the Harlem Cultural Festival, which took place over six weeks during that same summer of 1969? A new documentary—the directorial debut of Ahmir “Questlove” Thompson—brings to light 47 reels of rollicking footage that capture the energy of the crowds, the top talent (from Stevie Wonder to Nina Simone to B. B. King), and the sobering context of the festival, which came a year after Martin Luther King Jr.’s assassination. “It was a crazy, crazy, crazy period,” says one of those interviewed in the film. “We needed something to reach out and touch us. We needed that music.” —J.V.