“Human beatbox” Doug E. Fresh is one of the pivotal figures of hip-hop, who can accurately imitate drum machines and effects with just his mouth and a microphone. His early collaborations with Slick Rick — ”The Show” and “La Di Da Di” — are among the genre’s foundational hits. Funk Flex is more than just a DJ. He’s a hip-hop institution, a radio and club mainstay who has helped some of New York’s biggest artists and hits break out and continues to keep his finger on the pulse of hip-hop and R&B. These SummerStage alums are back with an old-school park jam reminiscent of hip-hop’s humble and joyous beginnings, celebrating the art form in which they’ve invested their lives, in the borough in which it was born.