Cloud Nine Music can certainly get into a groove. Trouble is, they can't get out of it. They've got the steady beat, the dependable keyboard line, and the bass riff you can latch onto — all creating a dance-party trance that will keep your head bopping.

But for a primarily instrumental band with lengthy theme-and-variation-style pieces, a little repetition goes a long way. Even though the keyboardist (Ryan Stroko) and the talented horn players (Ben Polcer on trumpet and Dave Luther on sax) trade off solo spots in most of the numbers, these musicians never seem to enter that frenzied improv state — that journey to a climax and resolution — that would make their jazz/electronica hybrid truly captivating. Instead, they have found a comfort zone of basic chord changes and austere melodies that doesn't challenge the band — or its listeners.

Cloud Nine's fans don't seem to mind. At a recent gig, the dance floor was packed a half hour before the band took the stage. Expectant, white twenty-somethings spoke of the band's "good vibe" and "energetic presence," and proceeded to bounce and flail to every song in the show. The beat was there (thanks to drummer Dan Piccolo and percussionist Justin Brewer), and every once in a while the full band seemed to find each other in a crescendo of new chords. But the wild movements of the dancers seemed to be responding to some daring musical line I couldn't hear.

Indeed, many of the songs on Cloud Nine's latest CD, Notice Co Lounge (a play on "no disco"), have an almost Music Minus One feel, like studio musicians laying down a rhythm track that still awaits a stunning lead instrument. They capture some great sounds, giving each song its own mood, from the spacey, sci-fi "Damage Control" to the bad 1970s TV soundtrack feel of "Dye Sub." But with songs averaging six or more minutes each, mesmerizing soon turns to boring.

Fortunately, a few tunes feature vocals by Jamie Register (who also plays bass) that fill in the soundscape, adding depth and confidence to the recordings. In addition to lyrics on the noteworthy soul numbers "Alright" and "When It Comes," Register also sings instrumental vocal on other tunes, and she isn't afraid to play with melodies or inflection in her improvisation. Her voice — smooth like Sade's and haunting like Astrud Gilberto's — deserves greater exposure. The need is especially noticeable in live performances, where Register is the band's stage presence — not just because she's the only woman and the only black member of the band, but because her seriousness of purpose radiates from her muscular arms, piercing eyes, and round bass sound.

Of course, the whole band is serious about its music, and maybe that's the problem. If these musicians really felt on cloud nine, they might be able to let go and surprise themselves.

Cloud Nine Music is at Leopold Bros. on Saturday, September 7, and at the Blind Pig on Friday, September 27.