No retrospective essay on a classic hip-hop album would be complete without someone saying something like “this record could never be made today.” It’s not that nobody is talented enough anymore to produce something as good as Paul’s Boutique or 3 Feet High and Rising, but rather that those records depend so heavily on sampling—and conventional wisdom says that the era is far behind us when beat makers could lift a guitar lick or drum fill without opening themselves up to a world of legal hurt. Though a few daredevils (most notably Girl Talk) are willing to play chicken with rights holders, and some high-end producers with sufficiently massive budgets can afford to pay to clear all the samples they want to use, most artists no longer have the option to incorporate someone else’s music into their own work, at least not if they want to sell the results.

Back in the 80s and early 90s—that is, before Biz Markie and Warner Brothers lost what turned out to be a landmark copyright case in late 1991—sampling was a much simpler process. Clearing one wasn’t generally prohibitively expensive, and samples shorter than a couple of seconds in length existed in a legal gray zone, where it wasn’t even certain that they needed to be cleared. (If a sample was so short or so heavily modified that it wouldn’t stick out, an artist might roll the dice and not even bring it up with his label.) Since then legal precedents like the one in the Markie case—usually handed down by judges with little understanding of remix culture—have demolished the notion of fair use when it comes to sampling. Lately the same sort of “copyright trolls” that have plagued other media—like the notorious Righthaven in the world of newspapers—have begun buying the rights to recordings that have become go-to sample sources, demanding exorbitant fees to use them, and pursuing scofflaws aggressively with the help of new audio-identifying technology. One such group, Bridgeport Music, won a 2005 case involving a two-second pitch-shifted Funkadelic sample that was nearly impossible to identify by ear.

Sampling has become such a minefield, even for artists who try to do everything by the book, that most musicians who work with samples have opted to go underground—they release their work for free on the Internet, which means it doesn’t generate money for them or for the artists they sample. This status quo looked likely to be permanent, but then last month a website called Legitmix started selling an El-P single called “Rush Over Bklyn,” a remix of his own “Drones Over Bklyn” that prominently features pieces of Rush’s “Tom Sawyer.” Nobody cleared any samples to make it, but it seems to be (no pun intended) completely legit.

Legitmix launched in July by releasing a 40-minute mix from DJ, producer, and pop-chart insurgent Diplo. It costs three dollars, plus the retail prices of however many of the 14 copyrighted tracks he spins you don’t already own (they’re available for purchase through Legitmix’s retail partner, MediaNet). The three dollars pays for an M3U file, which is essentially a list of instructions telling your music software how to play back the mix’s components. Usually M3U files are used to keep the songs on a digital album in the right order or to share simple playlists, but Legitmix files encode a higher order of complexity: to reproduce a DJ’s mixing, for instance, they might contain instructions to start a given track at the proper time to pick up the preceding cut’s beat, or to segue to the next track in just the right way.

Legitmix has taken off with DJs who might otherwise have to share their mixes for free, but El-P’s remix is the first to integrate an existing song so thoroughly into a new one. The associated M3U file tells your iTunes to play the massive opening break of “Tom Sawyer,” then play it again and again (alternating with other bits of the song) while simultaneously playing El-P’s rap. You don’t download El-P’s slice-and-dice of “Tom Sawyer”—you download a complete copy of “Tom Sawyer” and instructions to slice and dice it the way El-P intended. It’s a subtle distinction, but legally it makes a world of difference. The former would probably land El-P in hot water with Rush. The latter is technically no different from dropping the needle in different spots on a copy of Moving Pictures, which is still totally legal in all states.

“Effectively you’re owning the materials you’re mashing up,” says entertainment lawyer Vlad Radovanov. “And you’re mashing them up in real time, so it’s not any different from a DJ performing a mix in front of you every time. And if you own the copy that you’re performing, you have the right to perform it. As long as you’re not creating a derivative work and embodying it in a form of expression that’s permanent and distributing it, for example, you’re not violating copyright. You’re just performing copyrighted works that you own.”

It’s an ingenious way to game a copyright loophole, bordering on the devious—though Legitmix creator Omid McDonald doesn’t care for such characterizations. “Technology can make some of these things practical,” he says, “so it could be seen as a workaround or a loophole, but I prefer the thinking that it’s a new solution. But whatever term works. It does it in a way that really benefits everyone and I think really goes with the spirit of copyright law. Because copyright law’s there to foster new innovation and protect the rights of copyright holders, and right now neither is happening with the current system.”

That leads me to what’s maybe the most brilliant part of the whole setup: because El-P’s remix requires you to own an MP3 of “Tom Sawyer” to play it back properly, and because buying it through Legitmix is easier and quicker (though admittedly not cheaper) than hunting down a pirated copy, “Rush Over Bklyn” actually encourages people to buy “Tom Sawyer.” Rush may not see enough money from those purchases to equal whatever presumably insane sum they would’ve charged to clear the samples, but McDonald and Radovanov agree that it may be enough to keep them (and other rights holders sampled this way in the future) from challenging the Legitmix model in court.

This could not only make it so that the next Grey Album won’t have to be released as a bootleg but also demolish the idea that Paul’s Boutique couldn’t be made today. Actually, depending on how deep MediaNet’s catalog runs, an enterprising producer could probably re-create the album from scratch. Now that would be interesting.

For an interview with Legitmix creator Omid McDonald, visit the Bleader.