Race is very hard to tell from someone's voice:
Possibly, if you cloned a number of people, raised them without any exposure to society, and forced air through their vocal tracts, they might produce different overall sounds, depending on race, and purely as a matter of physiology and acoustics. Right now, however, there's no real evidence of a characteristic physiological voice produced by people of different races. What differences there are, physiologically, are more than overwhelmed by age, health, and the deliberate use of the social voice.
The Dish 