One of the most popular titles in the Kronos Quartet's by-now vast discography is their Pieces of Africa. Not coincidentally, it's also one of their most tonal and tuneful recordings, bringing compositions by African composers or composers drawing on African influences. A similar spirit of felicitous culture cross-stitching pervades the Soweto String Quartet's Zebra Crossing (RCA Victor 74321-26865; 40:41) , a cheekily named and thoroughly unpretentious contribution to the longhair world of string quartet music. The truth be told, the going is a bit too easy and glib at times, and the rhythm section grooves-as on the title track-tend to overly pop-ify the proceedings. The pop instinct continues with a medley of pieces from Paul Simon's Graceland, the controversial album that gave South African musicians international forum. Simon's tunes benefit beautifully from the one-for-all string quartet textures, analogous to the warm vocal mesh of Ladysmith Black Mambazo. The anthemic "Nkosi Sikelel" (God Bless Africa) is a lustrous jewel. In general, they bring a freshness and zeal to the medium, aligning with such Turtle Island String Quartet as an ensemble that leans in the direction of folk sonorities and embraces the improvisational imperative.