Reading John McWhorter's sharp piece on the "black" cadences Barack Obama drew upon in his inaugural address, I was struck by these lines:
And yet what makes Obama's linguistic repertory especially resonant as an American phenomenon is that he speaks Black English as a second language. Growing up with a white mother, he did not acquire it on her knee, nor does one come away from Hawaii and Indonesia steeped in the cadences of Jay-Z. Black English is, for Obama, part of the identity he constructed as a young adult.
I don't know whether there's a term for this phenomenon--that is, for speaking more beautifully in a voice developed later in life--but I believe it's a fairly common one. James Earl Jones, for instance, famously had a childhood stutter so debilitating that he spent eight years functionally mute before encountering a high school teacher who helped him work on his speech. And if I recall correctly, Richard Burton, whose first language was Welsh, always claimed that his world-famous voice was entirely ordinary when he spoke his native tongue.