ON STAGE, Chris Rock is a giant presence. The space unaffected by his skinny body, and that's most of it, is filled by his voice. Rock's voice rises in pitch and volume from a high tenor to his inevitable falsetto howls of righteous fury, drowned in the ensuing storms of laughter. Then the cycle begins again. He restlessly stalks from one wing to the other as he testifies the creed of pissed-off black America, or at least, pissed-off Chris Rock. And he is always, always funny.