Once the rage in Rocinha, Rio's biggest slum, hardcore funk dance parties have become tamer since police reasserted control last November after expelling drug barons who ruled the area for 30 years.

High up in a crudely constructed bare-concrete home in the favela of Mangueira, a Funk Carioca beat crackles from tinny smartphone speakers. It's the rhythm of Rio de Janeiro's vibrant hillside ...