It's not always easy to measure influence in hip-hop.

Sometimes, for an artist, it's an abstract thing: principles, subject matter, the ideology of a rapper's ideas and ideals. 

Sometimes it's a surface-level aesthetic approach: the sound, the production style, or a particular sensibility.

Then there's the vocal performance. Sometimes it's about a rapper's delivery, how his or her voice comes across. Other times, it's about his flow: the rhythmic pattern of his vocals over the track. Or maybe it's the lyrical approach, the way an artist writes or conceives of his punchlines or figurative language.

Any way you dice it, the DNA of hip-hop often evolves in unexpected ways. You can't always anticipate what the truly "groundbreaking" work is going to be. Although The Bomb Squad's production on Public Enemy's records was revolutionary and game-changing, it was also so singular that it only ended up showing in the artistic approach of artists like El-P years down the line. Whereas Dr. Dre's work on The Chronic was so influential because it was so replicable: it was the tack artists would take throughout the West Coast and the South, becoming the dominant sound of hip-hop for a full decade.

But what makes up the sound of now? We took a look at some of current hip-hop's most influential artists. Some are who you'd suspect. Others might be a little unexpected. Here are the 10 Major Influences On Today's Rap Sound.

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