Overtones is a column that examines how certain sounds linger in our minds and lives.

The first cellular bits of rap music I loved were phrases: "Wine and women and song and such"; "The rude Redman rip backbones and hips to bits"; "My vocals exact, like rack and pinion in a Jag." Growing up, I didn't argue about these lines, or write them down, or think about why they worked as well as they did. They just broke off from the surrounding air and claimed me. Suddenly, there were new voices muttering in my ears. They wouldn't leave me alone.

Rap music does this to people. Constantly scribbling over itself, scuffing out the marks made before, it is an inherently repetitive art, and thus a Petri dish for cultivating obsession. Repetition and obsession are intricately linked, and when I try to prize them apart I start to feel dizzy. Visual artist Richard Serra said that "repetition is the ritual of obsession," which feels about right—obsession is the belief, repetition the daily prayer.

This is part of why the act of loving rap music can feel so anxious and sharp: Music love is needy and grasping to begin with, built on something we can't see, something no two people can agree on. But rap, built on loops that keep restarting, presets that go on into infinity, and vocalists who are constantly reworking their language on the fly, digs into deeper neural grooves. Take ad-libs, for example: rappers cultivate them for practical reasons, so that we identify them the moment they appear on a track. For them, it has as much to do with hip-hop's roots in graffiti as with the dictates of personal branding, but for listeners, these tics function as the smallest observable units of a rapper's aura. The really good ad-libs propose an entire worldview in a syllable (Gucci Mane: "SKRRT! SKRRT!" Pusha T: "Egchk!”), and hearing them repeated from track to track stimulates the portion of our listening brain that knows how to differentiate the 4 a.m. hum of our kitchen from someone else's.

As humans, we are hardwired to crave this kind of repetition, especially when it varies slightly each time: Technically speaking, we seize upon similar clumps of raw sensory data in a process called feature extraction and then bundle them together in a process called perceptual binding. When we recognize a powerful phrase dancing from place to place in a rapper’s catalog—the same each time but in a different context—we are pleased on a subliminal level, in part because we are recognizing our own hard work. The pattern may have been there already, but we discovered it. When a rapper repeats a phrase for the thousandth time, it stirs all three zones of memory at once: echoic, which is parrot-level memory; short-term; and long-term. This is a profound sensation, and the artist who triggers it for us ends up looking pretty powerful by association.

In music, we tend to group aura and charisma under intangibles—just another god-given gift doled out unfairly to a select few at birth, like talent itself. But they aren't just given. They are built, painstakingly, through repetition. When I think about Nas' earliest freestyles, when he was just a kid with a demo tape, I think of just three words: "Son of Sam." He repeated them so many times that when they appeared on Illmatic, they felt like a catechism to the people who had been paying attention. Repetition triggers our "there's a puzzle here" sense; things accrete in significance as they echo.

"The way Black Hippy pass resonant phrases from one member to the next suggests an alternate universe with its own logic and laws."

Black Hippy—the crew, or movement, or something, that Kendrick Lamar heads along with Schoolboy Q, Ab-Soul, and Jay Rock—have invested a lot of energy into this sort of pattern recognition, and it accounts for a lot of their mystique. You can trace this behavior back to their earliest records, before the world was paying attention. The way they passed resonant phrases from one member to the next suggested a shared philosophy, an alternate universe with its own logic and laws. On "Hell Yea", from Ab-Soul's 2011 mixtape Longterm Mentality, Kendrick Lamar sang, “Motherfuck the government, motherfuck the system/ Motherfuck you, I’m just livin’ how I’m living." This powerful line reappears one year later, on Ab's "Bohemian Grove" from Control System, this time repurposed as a playful chant.

Tricks like these pop up everywhere on Black Hippy projects. “What’s your life about/ Enlighten me/ Is you gonna live on your knees or die on your feet?” Ab-Soul demands on Section.80's “Ab-Soul’s Outro” and then again on Control System’s “Track Two”. Schoolboy Q's "bet I got some weed," "you gon' get some dick tonight," and "Figg, get it, get it" chants pop up on both his Setbacks and Habits & Contradictions albums, little breadcrumbs linking one project to the next.

What these phrases have in common—save, maybe, for Schoolboy's "you gon' get some dick tonight”—is the suggestion of the value of power accrued through wisdom, a notion linking Black Hippy back to Wu-Tang Clan, the Ur-cult of rap. Like the members of the Wu, Black Hippy appear on each other's projects, but judiciously, careful to keep a safe aesthetic distance from each other. Occasionally, their guest appearances feel like little jokes: On Jay Rock’s “Bout That”, from 2011's Follow Me Home, Schoolboy Q raps exactly one bar with no fanfare and never reappears. On “Still a Regular Nigga”, from Ab-Soul’s Longterm Mentality 2, Jay Rock mutters only one word: “Nope.”

This leaves resonant phrases as the only concrete evidence that Black Hippy are, in fact, a group. (Schoolboy has teased, after all, that there will never be a Black Hippy album.) In some ways, these phrases are the group, the common energy crackling between them. This only becomes clearer as the members stray further from each other, pursuing distinct careers. On Schoolboy's new album Oxymoron, there are a few remnants of the old word game—Kendrick introduces his verse on "Collard Greens" with a quote from his "Backseat Freestyle"—but for the most part this is Schoolboy’s solo bid. On the one hand, Schoolboy has never sounded more like his own artist: On powerful autobiographical tracks like “Hoover Street” and “Prescription/Oxymoron”, he paints a world vivid enough and deep enough for us to get lost in all on its own.

Still, listeners are loathe to relinquish those perceptual bonds, especially ones that have been built up slowly over time, and Schoolboy's spell suffers in the transition. Radio bids like like “Man of the Year” or “Hell of a Night” are about as far from “mysterious” as you can get, and while neither song is bad or offensively banal, both work like neurological stop signs for anyone looking for traces of Black Hippyness—it's hard not to miss the powerful implication of something larger at stake. As listeners, we crave these hidden worlds, the promise of something coherent and tantalizing darting beneath the surface. We never want to see all of it, but we live for the suggestion that it exists.