In the 1970s, an underground urban movement known as "hip hop" began to form in the Bronx, New York City. It focused on emceeing (or MCing) over house parties and neighborhood block party events, held outdoors. Hip hop music has been a powerful medium for protesting the impact of legal institutions on minorities, particularly police and prisons. Historically, hip hop arose out of the ruins of a post-industrial and ravaged South Bronx, as a form of expression of urban Black and Latino youth, whom the public and political discourse had written off as marginalized communities. Jamaican-born DJ Clive "Kool Herc" Campbell pioneered the use of DJing percussion "breaks" in hip hop music. Beginning at Herc's home in a high-rise apartment at 1520 Sedgwick Avenue, the movement later spread across the entire borough. On August 11, 1973 DJ Kool Herc was the DJ at his sister's back-to-school party. He extended the beat of a record by using two record players, isolating the percussion "breaks" by using a mixer to switch between the two records. Kool Herc's sister, Cindy Campbell, produced and funded the Back to School Party that became the "Birth of Hip Hop.". Herc's experiments with making music with record players became what we now know as breaking or "scratching."