Underground rapper Aesop Rock will release his fourth album, "None Shall Pass," Aug. 28 via Definitive Jux. The set features contributions from longtime beat collaborator Blockhead as well as vocals f

Underground rapper Aesop Rock will release his fourth album, "None Shall Pass," Aug. 28 via Definitive Jux. The set features contributions from longtime beat collaborator Blockhead as well as vocals from Mountain Goats principal John Darnielle.

"The guy [Darnielle] is incredible," Aesop Rock tells Billboard.com. "[It was] one of the few times in my life where meeting the actual man behind the songs has lived up to its potential. He's not like a letdown of a hero, like so many others are. The truth is we just like each other's stuff."

"None Shall Pass" was recorded over the last two years in his home and mixed at Gotham Studios in New York. Earlier this year, Aesop Rock contributed an "original mix" for the Nike All Day workout series, but this record is his first proper release in four years. "I get so focused that I forget that people have to actually hear this sh*t some day, so those songs where I went of on weird tangents just to try something new ... I start thinking, are people gonna get this?," he says.

"Me and Blockhead are really like a well-oiled machine at this point," he continues. "One of the main differences was how much we mixed and matched samples with live instrumentation. A lot of it was pre-planned, but then at one point we ran into a handful of sample issues, and between me and a group of musicians I know, we had to restructure a good amount of the production. It ended up being this really hefty mix of samples and live stuff."

Aesop Rock has garnered a reputation for bleak lyrics that are backed by dark beats, and "None Shall Pass" continues in this vein, to a point. "It's probably not my darkest record, but it has its moments. There's actually a few pretty uplifting, or playful moments," he says. "But even my playful moments have a touch of bizarro world darkness."

After a handful of shows this summer, the rapper will tour North America beginning in early September with Rob Sonic, DJ Big Wiz, Blockhead and another act that he says will be an out-of-the-ordinary pairing.