With underground rap changing so quickly, it's hard to strictly define all the various underground rap subgenres. Thanks to the Internet and accessible technology, anyone can push forward a genre like underground rap with the few clicks of a mouse.
As the rate of musical change continues to accelerate, new subgenres of underground rap are born, die, and change every few minutes, it seems. Many older established subgenres are becoming more popular, even as fans have a hard time defining them exactly.
One example of a couple of underground rap styles that overlap are horrorcore rap and acid rap. Acid rap is probably the lesser-known and more contentious of the two underground rap styles. Both underground rap subgenres share certain stylistic elements, sonic approaches, and lyrical content.
But not all acid rap artists are horrorcore rap artists, and vice versa. To understand the difference between horrorcore rap and acid rap, we can first look at the history of both of these underground rap genres.
Horrorcore rap and acid rap developed around the same time, largely in the early '90s, though horrorcore rap can be said to date slightly earlier, to the late '80s.
One of the first horrorcore rap groups was the Geto Boys, who were known largely as a gangster rap group, but started weaving in horror movie-style imagery into their music. Their song "Chuckie," about the infamous murderous doll form the Child's Play movies, was considered one of the first horrorcore rap songs.
Much of the early horrorcore rap violence was not particularly realistic and was inspired by the fantasy of movies and television. Soon after the Geto Boys came some of the earliest artists who specializes almost exclusively in horrorcore rap, like Kool Keith and the Flatlinerz in New York.
Around the same time arose so-called "acid rap," which was the tag preferred by the Detroit artist Esham. He picked up many of the budding themes of horrorcore rap in his lyrics, but his sonic palette was a little broader.
The "acid rap" term was meant to nod at psychedelic rock, which often influenced the actual sound of his music, which fused typical hardcore hip-hop beats with metal and other elements. Esham also went beyond just talking about horror in his lyrics and talked about broader issues like paranoia and drug use.
Esham influenced many artists in both subgenres. Some picked up largely on just the acid rap part, focusing more on the psychedelia and trippy, drug-influenced vibe.
Other artists have later been tagged acid rap just for their unpredictable, crazy sound, even if they don't trace a direct lineage to Esham. For instance, some underground rap acts from outside of Esham's Detroit circle who have been called "acid rap" are Deltron 3030 and Cage.
Meanwhile, the hallmark of horrorcore rap is the lyrical content. Horrorcore rap may draw the sound of its beats from some acid rap, but horrorcore rap is largely about over-the-top, cartoonishly gory stories.
Some major artists have been influenced by both, like one of the most infamous underground rap groups of all time, Detroit's Insane Clown Posse. Taking the persona of murderous clowns, the group was so outrageous that it took horrorcore rap out of underground rap circles and into the mainstream.
However, they claimed Esham as a major influence, and they have always been among the most creative of the horrorcore rap acts, often incorporating a creative acid rap style to their beats.
Still, despite all this discussion, you shouldn't get too wrapped up in splitting underground rap hairs. Horrorcore rap, acid rap, whatever -- enjoy the music you enjoy and don't get caught up in labels.