Free improvisation is risky business — in the hands of lesser performers, it can come off as self-indulgent rambling or worse, a bunch playing at the same time as opposed to together. Fortunately, these two Bay Area-based hepcats and composition instructors at Oakland’s Mills College are essentially ready for anything. The classically trained Chris Brown (piano, electronics) has composed for both acoustic and electronic settings — the latter often of his own design — and played free jazz with the late Glenn Spearman’s Double Trio. Fred Frith (guitars) was a member of seminal UK art-rocker act Henry Cow, and John Zorn’s manically eclectic Naked City — he has recorded with the Residents, composed for classical ensembles, and has engaged in much solo/duo/etc improvisation. Though far from easy listening for most people, Cutter Heads, recorded live at Mills in ’02 and ’04, is proof-positive that free-improv discs are good for more than lease-breaking. “Nothing But Make Me” begins brittle and convulsive before evolving into surreally probing and pensive. Frith’s eerily humming, sighing, distant-sounding wails on “Sings The Foundation” are juxtaposed with Brown’s lyrical, crystalline, heartrending key strokes. If the concept of two master musicians spontaneously micromanaging sound and silence intrigues, Cutter Heads is a rare prize.