Public Enemy revolutionized hip-hop, expanding the music's sonic vocabulary while raising the stakes for its social impact. Chuck D, the group's leader and conceptualist, claimed at their peak that "rap music is the invisible TV station that Black America never had" and he ensured that Public Enemy addressed the concerns of Black America, picking up a thread left hanging by the radical soul and funk of the late 1960s and early '70s. Samples of this music drove the bracing, cacophonic productions of the Bomb Squad on the early Public Enemy albums for Def Jam, a dense, invigorating collage of beats and noise that underscored the urgency of Chuck D's rhymes.