There’s no denying hip-hop has changed. It was always changing.

From the moment the craft left that rec room at 1520 Sedgwick, the tenets of the culture have been in flux, but no single innovation proved as revolutionary as sampling.

The sampling boom of the late ‘80s, powered by the small-yet-powerful SP-1200, underwrote some of the genre’s fiercest critical acclaim. The enthusiasm wasn’t universal, however, particularly amongst the artists who were being sampled. In 1991, The Turtles sued De La Soul for their brief sample of “You Showed Me” on “Transmitting Live from Mars.” That sample—just a 12-second loop—reportedly cost the group as much as $1.7 million. Later the same year, Grand Upright Music, Ltd. v. Warner Bros. Records Inc., which saw singer-songwriter Gilbert O’Sullivan face off against emcee Biz Markie, instituted that oft-costly preapproval from sampled artists was required to avoid a lawsuit. “Alone Again,” the Markie track in question, was removed from subsequent pressings of I Need A Haircut, a seismic shift disguised as a minor concession.

Sampling didn’t die—something Biz himself proved with 1993’s All Samples Cleared!—but it was bruised severely; imbued with paranoia, skepticism, and label reservations. The craft became more straightforward, and subsequent producers favored obscurities and interpolations over anything potentially costly. Sampling was still the backbone of the genre, but it was a brittler one. Hip-hop, however, is a resilient art. Strange though it may seem, some of the decade’s most essential and forward-thinking artists have been redefining sampling alongside a ninety-two-year-old business model.

In November 2011, Madlib released “Thuggin’,” the first outing from his then-novel collaboration with Gary, Indiana native Freddie Gibbs. The record proved the unlikely interplay between two far-removed acts, but the focal point of “Thuggin’” wasn’t the producer or the emcee; it was the musicians who furnished the track’s cosmic instrumental—an otherworldly slice of prog rock that may as well have been pulled from the Dark Side of the Moon demos. That couldn’t be further from the case: “Thuggin’” was built atop an affecting slice of library music, one of contemporary hip-hop’s most unlikely and intriguing influences.

Rubba, the outfit behind the track in question, were commissioned by De Wolfe Music—the originators of the library music model—prizing corporate ownership and ease of commercial licensing over artistic recognition. Helmed by library music legend Jacky Giordano, Rubba comprised Tim Broughton, Alan Howe, Robert Poole, and John and Monica Hyde, all experienced instrumentalists and writers careening throughout the hidden scene. From the album art and writing credits to the stake of the copyright, De Wolfe eclipses Rubba, obscuring the musicians while promoting the company itself.

De Wolfe—founded in 1909—initially accrued an extensive library of sheet music, played on request as accompaniment for silent films. It wasn’t until 1927, following the advent of sound recording, that De Wolfe developed the first modern music library. It was a repository of commissioned tracks and projects owned entirely by the company itself and licensed for media use. Throughout the ‘30s, their growing catalog was used mostly to score newsreels from British Pathé and British Movietone News. By the ‘60s, De Wolfe’s library impacted media such as Doctor Who, Monty Python’s Flying Circus, Dawn of the Dead, and Return to the 36th Chambers. All the while, they branched out into genres such as rock, folk, and jazz, embracing strains of world music and continuing to pioneer the then-commonplace model.

Familiar though it may be, library music remains a strange phenomenon, operating by a rationale effectively antithetical to popular music. Whereas conventional artists record their music in the hopes of a commercial release, those behind library music compose and record for the interstitial, scoring the transitional moments otherwise forgotten by directors, showrunners, and broadcasters. In retaining the complete copyright, a music library such as De Wolfe’s can license this music without consulting the musicians, forgoing the issues of traditional licensing that plague the oft-expensive and occasionally litigious art of sampling.

If affordable licensing endears library music to hip-hop producers, the lack of commercial concessions comes as a bonus. You won’t find any radio singles on Rubba’s In Motion: the album’s not for sale, the fans are non-existent, and the musicians are free from marketing and A&R. In one regard, Rubba is beholden to the whims of a faceless corporation, but on the other, the collective is liberated from the demands of the record-buying public. It’s no surprise that Madlib would appreciate such affordable and unbridled art.

Madlib is far from the only one. Though his use of “Way Star” is the most definitive use, the spacey cut has been flipped over 20 times since; it remains Rubba’s standout track, though “Carousel in the Milky Way” was sampled by The Avalanches in 2016.

De Wolfe’s deeper catalog has proven similarly popular. Though Simon Park has furnished tracks by Quasimoto (“Don’t Blink”) and The Game (“Wonderful Life”), he found more sampling success as Simon Haseley, the pseudonym responsible for samples from JAY-Z (“Don’t You Know”), Beyoncé (“A Woman Like Me”), DANGERDOOM (“Perfect Hair II”), Company Flow (“Bee Aware”), and El-P (“Kids No Wins”). Even today, De Wolfe contractor Roger Webb may be the only one to have linked up with A$AP Rocky (“Tony Tone”), Flying Lotus (“Heat Wave II”), RZA (“Tragedy”), Swizz Beatz (“Where The Cash At?”), and Ghostface Killah (“Loyalty”).

That’s saying nothing of the other large library catalogs, each one a treasure trove of passages and elements. Selections from KPM’s catalog have underpinned tracks from Knxwledge (“Nvrending”), JAY-Z (“Stick 2 The Script”), Drake (“Summer Sixteen”), Gorillaz (“Latin Simone”), and ScHoolboy Q (“My Hatin’ Joint”), with artists such as Alan Hawkshaw proving the most popular amongst producers. Madlib himself dipped into the Bosworth Music Library for Madvillain’s “Meat Grinder,” and DANGERDOOM would later rap over a famed KPM library selection on “Old School.” Sylvester-signed outfit Network laid “Tinted Glass” thirty-five years before Drake took it “running through the six with [his] woes.”

Library music is hip-hop’s secret weapon. It’s simultaneously everywhere and nowhere, underpinning classic tracks while hardly possessing an identity of its own. Sampling is often expensive, as in the case of Danny Brown; protracted, as in the case of MadGibbs; or legally questionable, as in the case of nearly every Kanye record. But library music exists as an artistic time capsule, earnestly antiquated yet both accessible and unmined. With the business structure itself shaping how some pioneering producers go about their craft, however, the impact of the library approach goes deeper than just direct invocation.

Enter: Frank Dukes, one of the decade’s most prolific producers and the founder of the Kingsway Music Library—a repository of sample-ready compositions recorded by a swathe of contemporary musicians. Though initially intended for Dukes’ leftover compositions, the library evolved into a bastion for productive musicians to showcase their interstitial work and offer their musical fragments to entrepreneurial producers and beleaguered crate diggers.

Dukes’ approach involves recording off older instruments and antiquated amps, helping him achieve a sound analogous to the classic records he’d otherwise want to sample. “I love music with real instruments,” he told Complex in 2016. “I’m not one of those guys that’s a purist about analog vs. digital, but I love the analog approach. Sonically, I connect to that.” In achieving the aesthetic while averting the clearance issues, Dukes is pushing sampling into the now. He has traded contrivance for affordability.

That’s not to say that Dukes’ instrumentals are disingenuous or obvious. While it has a long way to go before it can claim to rival De Wolfe or KPM, Kingsway has had its fair share of successes: Dukes’ “Couches” was sampled on Kanye’s “Real Friends”; “Vibez” was flipped on Drake’s “0 to 100/the Catch Up”; “Studio B 121” underpinned Kendrick’s “Untitled 07 Levitate”; “Pianoparts” reared its head on J. Cole’s “Immortal.” Even Madlib, the patron saint of crate diggers, pulled one of Dukes’ fleeting instrumentals for Bandana cut “Half Manne Half Cocaine.” The fact that these flips have been hiding in plain sight is itself an achievement, highlighting just how effectively Dukes’ approach channels the spirit of musical eras past.

Still, there’s something to be said for the thrill of the find: that perfect flip, hidden in the middle of some unheralded record, possibly being the passage that launches a career or dominates a summer. Sampling was built on this thrill. As legal precedents have forced diggers further underground, they’ve gone from curios to musical archaeologists—digging deeper, still in pursuit of some strange, affordable moment.

Their efforts aren’t in vain. The internet is a great democratizer, and interest in samples—library or otherwise—is stoked by their newfound accessibility. “Way Star,” once little more than a footnote in an already-unheralded career, has accrued over two million views. Earlier this year, the entirety of Rubba’s In Motion was officially released on vinyl for the first time, a testament to the transformative power of artistic re-contextualization.

It’s this idea of re-contextualization linking everything from De Wolfe and Kingsway to KPM and The Hollywood Edge.

The possibilities of pre-recorded sounds are limited only by the vision of the producer, each record akin to an instrument that listeners must first realize. It seems only right that sampling, one of hip-hop’s most revered and persistent tenets, should come to redefine itself in the image of its antiquated flips. Adaptation is the essence of the art form, and Dukes’ faux-retro sounds represent a new frontier for the craft. It’s been decades since sampling was uninhibited, but library music has presented both a treasure trove of tracks and an opportunity for reinvigoration.

Hip-hop’s obsession with library music is steeped in the sounds of the past. Now, that very system may be the genre’s future, helping reinvent and revitalize the sampling culture in an increasingly litigious industry.