Pinpointing the actual birthday of a musical genre can be an inexact science. Did rock n' roll really begin with Elvis' swinging hips or before that in nondescript blues-oriented jam sessions in the South? Where did the blues itself start? One of the reasons hip-hop is unique is that we basically agree on an exact moment of origin.

While it is sometimes contested, August 11 is widely believed to be hip-hop's birthday. Today, in 1973, Kool Herc put together one of his famous soundsystems for his sister's birthday party at 1520 Sedgwick Avenue in the Bronx. This wasn't the first time that Herc attempted to DJ, but was certainly the moment that he displayed the genius move of putting the same record on two turntables simultaneously. One housed an original track, which he cut and flipped on rhythm. The other was just used for a song's break beat -- a move that accentuated the vocals on the first turntable and gave them a hard beat to navigate over.

"Kool Herc brought the idea of the Jamaican soundsystem to America," says Marcus Reeves, a journalist and the author of 'Somebody Scream! Rap Music's Rise to Prominence in the Aftershock of Black Power.' "His innovation was bringing the break beat to the sound of this new movement. He would just kind of drop a needle on the record, and just kind of go back and forth."

It sounds simple enough, but what Herc did on August 11 was a completely new innovation in sound. It still forms the basis of the hip-hop we listen to, love, party to and argue about to this day.