Louisiana-based harmonica player Raful Neal hasn't achieved the mainstream recognition of his Chicago counterparts, but among aficionados he's a highly regarded instrumentalist, singer, and songwriter. Known as the "Little Walter of Louisiana," he owes much of his style to the Chicago harp master--including his unorthodox upside-down blowing technique--but his gritty voice is more deeply expressive than Walter's, and his music has a sly, backwoods funkiness that characterizes classic Louisiana "swamp boogie." His family band backs him with an instinctive empathy born of a lifetime of jamming together; at their best, Raful and his brothers--especially lead guitarist Kenny Neal--present one of the tightest and most imaginative blues shows you're likely to see for a long time. Tonight, Rosa's Lounge, 3420 W. Armitage; 342-0452. Saturday, 10 PM, SS Chicago Princess, Navy Pier, Grand Ave. at the lake; 342-0452.