The intensity of the rhythms on Interstring’s Winter Song is a thing of beauty. Never settling into an easy or repetitive loop, these musicians are constantly and aggressively striving to create new harmonic sounds and time signatures. This makes for a collection of unsettling, harshly impressive tracks. A gathering of four local jazz artists who have returned to the Kansas City area after gaining fame elsewhere, Interstring is led by Bob Bowman, whose thrilling work on the acoustic bass is the centerpiece of such joyrides as “Forever, I Hope” and “New Year.” At times poundingly rhythmic, at times heart-stirringly melodic, Bowman always holds the material firmly in the grip of his able hands. Danny Embrey and Rod Fleeman provide the guitar accompaniment to Bowman’s stunning foundation. This proliferation of guitarists explains the band’s name and defines the unique sound of its music. Embrey’s electric guitar work can be surprisingly subtle when he’s providing rhythm, yet he frequently busts out killer solos. Fleeman is equally imposing, and the beautiful melody of his melancholy “Election ’92” is excellently fleshed out by the rest of the ensemble. What is most admirable about Interstring is the way its members ably shift from style to style. Drummer Todd Strait provides rhythms that evoke samba, reggae, and blues, and the rest of the group is always dead-on in the rather abrupt changes. This makes for music that constantly defies expectations, which is the very essence of quality jazz.