THERE IS A BOX TO the left of Tavis Smiley in the broadcast studio, a box with knobs and dials and cords running in and out of it. There is a row of green lights on the box, flashing every time Smiley's voice rises above the level of normal conversation and enters the danger zone. National Public Radio has built a reputation on smooth, professional broadcast voices, projecting authority, repose, and, let's face it, geographic anonymity—these voices come from anywhere and nowhere. They tend to be "white" timbres, usually without much of an accent or any other cultural...