The Mars Volta has always been about the noise — the rolling, room-shaking, mind-blowing and beautiful noise. On their fifth album, Octahedron, they go kinda quiet, turning down the amps and turning up the soft lights. The lyrics are still so cryptic you’ll need Wikipedia and a bong to help penetrate them, and there’s still a heavy air of pretension hovering over the eight songs. But the Mars Volta sounds like a band uncertain of its future on Octahedron. Apparently they got tired of twisting and turning at 400 mph for marathon sessions, since only one song breaks the eight-minute mark (there are three seven-minute tunes, so don’t worry, endurance fans). Yet without their speed and noise, frontmen Omar Rodriguez Lopez and Cedric Bixler Zavala sound lost in the cosmos. The opening “Since We’ve Been Wrong” takes more than 100 seconds to break out of its slow drone with some actual music. It also gives you a pretty good idea where Octahedron is headed and why it stumbles so often. “Communion-shaped serpent rays in prism-tail rainbows escape,” Zavala sings on “Halo of Nembutals,” sounding like one of those incomprehensible prog-rockers people used to make fun of. It’s really nothing new for these not-so-closeted prog-rockers, but the Mars Volta used to conceal lines like that in knockout tunnels of noise, not acoustic guitars and plodding 4/4 rhythms. The Mars Volta play House of Blues (308 Euclid Ave., 216.523.2583, houseofblues.com) at 9 p.m. Tickets: $35. —Michael Gallucci
