The Black Keys, Dan Auerbach’s blues-rock duo, have always seemed to hold to their well-established sound. The two-man band has made four full-length albums since their debut, “The Big Come Up,” in 2002, hardly altering their spare, heavy blues between their first album and their latest, “Attack & Release.”

Too unprocessed and deferential to have any place in the pop world; too no-nonsense and slow to really belong in the world of indie rock; and lacking a “Seven Nation Army”-style breakthrough hit, the Keys have been making their music for a scattered and diverse audience devoted to their remarkably consistent output. So it might come as something of a shock to hear Dan Auerbach altering his sound a bit on his new solo album “Keep It Hid.”

One of that new brand of solo album that includes more instrumentation than on the band’s regular output, “Keep it Hid” finds guitarist Dan Auerbach attempting to push his sound outside of the usual boundaries of a Black Keys album. Part of this expansion involves experimenting with levels of diminished intensity outside of the Keys’ consistently heavy-handed work. The album crafts a clearer arc than anything previously released by the Keys, starting slowly and lifting up to a peak before settling down gently on the delicate Taj Mahal-like final track “Goin’ Home.”

The album’s opener, “Trouble Weighs a Ton,” makes clear the new direction Auerbach is taking. He seems to be doing homage to an older, gentler side of the blues genre, keeping the volume low as he crows moodily over his minimal strumming. Auerbach is a skilled guitar player with a wistful voice, and “Trouble Weighs a Ton” is certainly an unobjectionable song, but as an album starter, it falls a bit short. Rather than moving in its gentle simplicity, the song feels generic and a bit boring, crawling rather than coasting slowly along. Perhaps more than anything, it feels like Auerbach, whose love of blues rock almost burst from his past albums, simply isn’t excited by the slower paced song.

The album soon picks up with “I Want You More,” as Auerbach both moves into more familiar territory and expands his sound in interesting ways. With his guitar growling like a bass and his intense voice snarling coarsely on top of it, Auerbach creates a smoky, back-alley vibe very much like that of a Tom Waits song.

The album continues its slow crescendo, building up the intensity through the driving rhythm of “Heartbroken, In Disrepair,” the moodier, organ-driven “Real Desire,” and the raspy, Creedence Clearwater Revival-sounding “Mean Monsoon,” before hitting the album’s drum-dominated peak, “The Prowl.”

“The Prowl” is at once extremely similar to and strikingly different from the typical Black Keys song. While much of “Keep It Hid” seems to be aiming for a more organic, varied sound, “The Prowl,” the hardest-hitting song on the album, feels neater and more contained than any similarly heavy Keys track. Auerbach mans the drums on this song—as on the rest of the album—and here especially one can feel the difference between his drumming and Black Keys drummer Patrick Carney’s. Where Carney’s messy pounding would propel the songs forward, Auerbach’s careful, more articulated syncopation gives them a more polished feel. This distinction, not necessarily a positive or negative one, is one that applies to the album as a whole.

“The Prowl,” and the album in which it is situated, is more measured and quiet than Black Keys works. “Keep It Hid” isn’t a flawless album, it doesn’t conform in every way to what we’ve come to expect from the artist who produced it, and it may disappoint hardcore fans. But listening to Auerbach tracing out new territory is certainly an engaging experience.