Audra McDonald gives an outstanding performance as Billie Holiday in Lady Day at Emerson's Bar & Grill.

You will undoubtedly hear that what Audra McDonald is doing as Billie Holiday in Lady Day at Emerson’s Bar & Grill is not an impersonation. It is, though. However much more it eventually becomes, it starts with capturing that eccentric, heartbreaking voice — and the capture is uncanny. Right from the first syllables of “I Wonder Where Our Love Has Gone,” which opens the show, McDonald nails the pinched tone, side-mouth delivery, and precipitous register leaps of Holiday in her heyday. Consonants are negotiable: “love” is more like “luhw.” Final vowels become dramatic opportunities: “Hear my plea-uh and hurry home to me-uh!” Pitch is obscure or even absent; some notes sound fried in place yet remain part of the melody. McDonald’s Holiday doesn’t so much sing as play her voice, like a saxophone, with perfect confidence in (or indifference to) its expressive powers.