In 2006 — nearly 20 years removed from their debut, Licensed to Ill, and two-plus years since their previous album, To the Five Boroughs — the Beastie Boys entered the studio with the intent of throwing fans a curve ball: an all-instrumental album that they called The Mix-Up.

Certainly, listeners knew the group was adept at playing the role of a power trio (Mike "Mike D." Diamond on drums, Adam "Ad-Rock" Horovitz on guitar, and Adam "MCA" Yauch on bass), as they had recorded their own backing tracks on 1992's Check Your Head and much of 1994's Ill Communication, not to mention their early punk singles. A vocal-free effort, though, was an unexpected development and not, as some might have suspected, a joke release. The Mix-Up, released on June 26, 2007—was quite a serious undertaking.

According to Yauch, the band embraced a new approach as a way to spur creativity. "We used a lot of older instruments, a lot of older recording techniques," he explained to MTV Europe shortly after the album dropped. "We used an old Neve console, old analog outboard gear. The instruments we recorded on were stuff from the '60s and '70s, maybe early '80s. It just makes you work in a different way when you use older equipment."

As Yauch noted, working through the limitations of older technology was a plus. "It's interesting when you're doing a record to have certain parameters. On [To the Five Boroughs] we just focused on using drum machines, synthesizers, sequencers, like programming stuff, sampling. On this one, we just started in on it, playing the instruments and it seemed like it would be interesting to do it without sampling, without turntables, and without vocals. Sometimes it's just interesting to work with a certain set of guidelines."

Those guidelines included dressing the part, wearing suits and ties to the studio every day. "All that, I feel, influences the sound," Yauch said.

It was a familiar sound—a funky stew of R&B and soul-jazz influences, with old friends Money Mark (keyboards) and Alfredo Ortiz (percussion) joining the fun. And there are some real highlights. "14th St. Break" busts in with feedback, spooky keys and a thin, distorted guitar taking the melody on the "verses." All the while, Diamond lays down a steady-as-stone beat and Yauch does his best Jaco Pastorius, laying down some funky, high-on-the-neck bass. The killer, unexpected moment is the four-bar breakdown about halfway through the song—it should be a sample of its own on someone else's record.

Listen to the Beastie Boys perform "14th St. Break"

"Electric Worm" sounds like some tamer samples of '70s jazz funk—wah-wahed organ sliding into wah-wahed guitar, while the bass walks and recedes beneath them. The same goes for "Off the Grid," where the clavinet figure that opens the song evolves into a tense section in which the distortion in that instrument melds with the clean tone on Horovitz's guitar, until the distortion rubs off on the clean tone and the fuzz from each instrument play with one another for a bit, as the beat propels them forward.

This both is and isn't background music. Beasties may not have been the MGs, but they knew their way around a groove, and these songs have grooves aplenty. Still, it wouldn’t have been a bad idea to write verses for some of the songs. "The Gala Event" is noisy and intense, due to the insistent bass and background percussion and layered in guitar effects—it would be a great track over which to lay down a rhyme or three.

Listen to the Beastie Boys perform "The Gala Event"

One thing The Mix-Up is not, is a critique of hip-hop, as if the Beasties would make a funky instrumental record because they were tired of the form for which they were known.

"We get asked, ‘What do you think of the state of hip-hop today?’" Diamond noted in an interview with The Aquariun Weekly. "Maybe I’m being defensive, but it seems like people always look for us to come out and criticize hip-hop. But hip-hop is what we grew up on, and it continues to be one of the only forms of music left that strives on evolution and innovation. Yeah, we might be in a spell where we’re waiting for that next record to come out and change everything—but still, that’s what hip-hop is and that’s what puts it in its unique place."

Ultimately, having made an album as different—and as good—as The Mix-Up was a source of pride in itself.

"That was our best idea," Horovitz told MTV Europe. "We've got other ideas, but at the time we were recording it, that's what we came up with. We're pretty pleased with ourselves on this one."