Chronologically, the history of vocal jazz squeezes Carmen McRae between Sarah Vaughan and Betty Carter; stylistic comparisons prove a good deal more difficult. There's no doubt that her scat singing was first influenced by Vaughan's, but McRae improvises with the swagger of a Texas tenor saxist; similarly, she had clearly heard and loved Billie Holiday, but brought a new, modernist edge to Lady Day's deflowered sensibility of long-lost innocence. McRae is tough: in person and in music, she suffers fools not at all, and sentimentality is spat on. Ballsy and bluesy, she sings of romance but her eyes are not just open--they're X rays, examining the words, her own emotions, and even the audience for the slightest hint of phoniness. At times, her music suggests a bitterness, even despair, but you'd be hard pressed to find a life in which those things are absent; it's just that Carmen McRae makes no attempt to cover them over, using her dramatic swoops and sometimes stunning expressivity to remake such knowledge into a particularly incisive art. Tonight through Sunday, George's, 230 W. Kinzie; 644-2290.