A 75-foot headphone cord plugged into Aunt June’s stereo system wound through furniture in the living room, across the kitchen floor and down a narrow stairwell into a pair of headphones attached to a 10-year-old Howie Cort. She was focusing on matching the beat of songs, one by one, from her cousin Greg’s record collection. From Strawberry Alarm Clock to The Doors, Aretha Franklin and more, Howie sat in that basement as much as she…