On a mild Monday afternoon in mid-January, Ester Dean, a songwriter and vocalist, arrived at Roc the Mic Studios, on West Twenty-seventh Street in Manhattan, for the first of five days of songwriting sessions. Her engineer, Aubry Delaine, whom she calls Big Juice, accompanied her. Dean picked up an iced coffee at a Starbucks on Seventh Avenue, took the elevator up to Roc the Mic, and passed through a lounge that had a pool table covered in taupe-colored felt. Two sets of soundproofed doors led to the control room, a windowless cockpit that might have been the flight deck of a spaceship.