In jazz, the term “cats” is bestowed upon musicians capable of swinging at the highest order. Likely, when hip-hop icon Chuck D coincidentally found himself in the studio during a Circles Around the Sun session for this sophomore effort, Let it Wander, he was simply voicing the acronym for the quartet when he dropped “cats” into his impromptu intro on “One for Chuck.” Yet, after listening to the double-album follow-up and all of its daring improvisational dances, it’s possible to surmise Chuck D could just as well have been referring to the four in that reverential jargon of jazz.

No question the seven songs rely upon the absence of boundaries, but that’s not to imply they are without discernible structure. Like a jazz piece, the compositions are anchored by repeating riffs that inform the ensuing solos, but once set free, become expressions without rules. There is a tangible feeling of daybreak on the opening “On My Mind,” as guitarist Neal Casal lays clean lines over the multi-keyboard bed from Adam MacDougall. Drummer Mark Levy plays it relatively straight, letting guest percussionist Jeff Franca provide the rhythmic counterpoint.

The up-tempo swing of “One for Chuck,” follows with be-bopping major key brightness sliding into a mirror-ball, roller-rink underworld, as Casal modulates a distortion-laced outpouring. The emphatically sustained bends of notes continues into “Immovable Object,” as Casal and MacDougall weave trippier tapestries, turning to an everlasting pattern, angular and shifting time, on “Halicarnassus.” Multitudes of compelling musical conversations between the two, and at times, even between MacDougall and himself, mark the finale closing out disc one.

The second half picks up where the first leaves off; with cycling, hovercraft riffs that dissolve into the atmosphere around them. Dan Horne is a cinderblock on bass; the exact grounded support needed for such flights, keeping the groove omnipresent as the other sonic excursions separate, then filter away. The clavinet funk of “Tacoma Narrows,” and the fusion rock of “Electric Chair (Don’t Sit There),” with its warbling into the echo chamber, suggest a residency in the 1970s, and it’s a fair point.

More significantly, however, Circles Around the Sun excels at sifting out any dated kitsch from the bell-bottomed decade, borrowing its best sonic and stylistic contributions and progressively coupling them with present-day advent. When they emerge on a coda from MacDougall reenergized from a lengthy tour of the cosmic haunted house in “Ticket to Helix NGC 7293,” bringing it all back down to Earth, the CATS return having once again completed another wondrous revolution on the interstellar loop.