Unless you plan on spending your summer at a silent meditation retreat, over the next few months you’re going to be hearing a lot of Playboi Carti’s breakout single “Magnolia,” which has all of the telltale signs of a summer-owning street-rap smash. The beat–courtesy of newcomer Pi’erre Bourne–is a monster, with an adipose bass line that seems destined to blow out car speakers across the country. The song’s meandering structure revolves around an instantly memorable (and instantly meme-able) hook, and maybe most importantly, it’s got the all-important “oh shit” X factor, that ineffable little quirk—like Young M.A.’s strangely addictive wordless groan, or Bobby Shmurda’s disappearing hat—that elevates an otherwise merely enjoyable rap song to summertime greatness.

In the case of “Magnolia,” it’s the exhaled pfshew sound that Carti, acting as his own backup vocalist, makes between each line of the chorus, as in “In New York I Milly Rock (pfshew) / hide it in my sock (pfshew) / Running from an opp (pfshew) / and I shoot at opp (pfshew).” This little riff does a lot of work. It provides a rhythmic counterpoint to the lead vocal, for one. It acts as a running punchline to the lyrics, standing in onomatopoeically for, at different points, Carti’s finesse at slinging crack, his agility at evading the cops, the gunshots he aims at rivals, and his skill at the Milly Rock, a dance that was itself the subject of its own summer street banger. It also makes “Magnolia” intensely addictive, the kind of thing you might run back a half-dozen times or so during your commute, just to hear Carti make that sound.

Ad libs, as these vocal asides are known, have been a part of the rapper’s toolkit for ages, but over the years they’ve evolved to become increasingly complex, and increasingly important to the songs they show up in. Go back to your favorite rap songs from the turn of the century and you probably won’t hear many ad libs at all; the ones you will hear tend to take the form of the occasional “uh” or “yeah” or “come on” that hype men typically provide in live performances. Compare that to Desiigner’s “Panda” from last year, where the densely packed ad libs do more to move the song along than the lead vocal. Odds are you don’t know any of the lyrics beyond “I got broads in Atlanta,” but you can probably sing along to every “brrrrah” and “git git git” the song throws your way.

Odds are you don’t know any of the lyrics beyond “I got broads in Atlanta,” but you can probably sing along to every “brrrrah” and “git git git” the song throws your way.

The rise of the ad lib roughly follows the shift of hip-hop’s center of power from New York City to the South. Harlem’s Dipset were early innovators in pushing the ad lib from basic hype man duties to something more abstract and interesting, but it was mid-aughts hits bubbling up from the South like T.I.’s “What You Know” and Jeezy’s “Go Crazy” that pushed ad libs into the spotlight. (In 2007, Kanye–ever in tune with hip-hop trends—brilliantly boiled down Jeezy’s appeal by giving him a guest spot on “Can’t Tell Me Nothing” that consists entirely of his sepulchral cackling.) A decade later, the South got rap’s steering wheel firmly in its hands, and thanks to artists like Young Thug, 2 Chainz, and Future, Southern-born ad libs like the “skrrt skrrt” sound of a car peeling out have become a part of the hip-hop lexicon, despite not technically being words.

In some ways, the elevation of ad libs in rap music resembles the guitar solo’s rise to dominance in rock ‘n roll a half century ago. As recently as the late ‘60s, lead guitar parts were mostly there to prop up the vocal melody, but within a decade they’d come to rival, or even outshine, the lead singer. Soon you had to have a wailing solo somewhere in your song just for people to take you seriously.

Unlike guitar solos, which tend to be graded largely on their technical difficulty, contemporary ad libs are evaluated on a range of qualities: funniness, the element of surprise, the odds that you’re going to rap along to them instead of the main vocal. Which means Migos are the Eddie Van Halen of the ad lib. In the couple years since they broke out with “Versace,” which many observers initially mistook for a one-time novelty hit, the trio has unexpectedly emerged as one of the most lyrically fascinating acts in rap, and ad libs are a huge part of their arsenal. Their latest album, Culture, packs ad libs into every available second, doubling and even tripling each member’s vocal presence, to the point where the verbal density of their songs can rival, say, the pummeling barrage of ad-lib-free sixteenth-note syllables Kendrick Lamar delivers on “DNA.” They serve a variety of purposes: providing punchlines, announcing Offset’s verses, occasionally providing entire alternate vocal leads, and generally just making everything livelier and more fun. There are more incredible ad lib moments on Culture than I can count: Offset following up the line “Bitch I’m a dog” with a double-ad-libbed “roof, grr.” The “flash” after Quavo says “I ain't really here to take no pictures” on “Get Right Witcha.” The bit on the ad-lib-packed “Call Casting” where Quavo hits you with wordless syllables vocoded into abstraction–the ad lib as pure sound design.

Migos are the Eddie Van Halen of the ad lib.

Ad libs play such an important role on Culture that during one listen I started to imagine a version of the album that strips away all the lead vocals, leaving only the instruments and ad libs. (I may have been mildly-to-moderately stoned at the time.) After speaking to some industry contacts, within a week I had an ad-libs-only version of “Bad and Boujee” in my inbox. It was even better than I’d imagined: cluster after cluster of delay-drenched words and sounds that seemed to bear no relation to each other—“bad / blaow / savage / grrah”—drifting over Metro Boomin’s darkly aquatic beat, the whole thing felt like a trap equivalent of a dub reggae song, reconnecting rap’s most up-to-the-second sound to one of the genre’s bedrock influences.

After the song’s viral blow-up, I tend to skip the album version when I listen to Culture on Spotify, but I keep going back to the ad-lib dub version again and again. In a perfect world, it would be there on my streaming service right next to the original.

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