Boca Negra, the title of fourth Chicago Underground Duo album comes from the Tenerife Canary Island, and means "Black Mouth." It is defined as both a verb -- “the endless intake of information” -- and as a noun: it's the local's name for the Tiede volcano. How the former relates to the music here is directly relational. Cornet player Rob Mazurek and drummer, vibraphonist, and mbira player Chad Taylor, also use computers and electronics. They overdub considerably in places, but it doesn’t detract from the immediacy of these compositions and the attendant improvisation within them. This set marks the first occasion the CUD has recorded outside of Chicago (it was recorded in Sao Paulo, Brazil by Matthew Lux); it also marks the first occasion the pair includes a cover: Ornette Coleman's “Broken Shadows.” On it, Taylor plays drums and vibes simultaneously. Mazurek’s cornet handles the head and bridge; he suddenly lays out as Taylor takes the chorus, creating an unfamiliar yet enchanting lyric feel. The bridge is imprecise; sometimes it extends into the chorus, at others, it simply vanishes, creating a disorienting effect that reflects the title; “shadows” of the bridge and the other structural elements remain with the listener as improvised notions actually replace them. The haunting “Hermeto” utilizes programmed ambient soundscapes and evolving percussion with a gently assertive Mazurek melody line that evokes Brazilian folk traditions. “Spy on the Floor,” is based on the blues and film noir soundtrack themes. Mazurek’s tense thriller-esque intro gives way to Taylor's big, rolling snare, and ultimately, a driving lyric architecture that asserts itself and then collapses: it gives way to shifting dynamics and instrumental interludes on vibes and effects. “Confliction”'s time signatures are directly at odds, yet their angles offer a palette for engagement and harmonic improvisation that bridges the gap seamlessly, making the tune nearly hummable in places. Boca Negra is the most sophisticated and improvisationally complex recording CUD has ever recorded, while easily being its most accessible.