What determines your character’s voice actor in TOR

I started up a Human Republic Commando in TOR, and was delighted to be greeted with the delightful sound of Jennifer Hale.

So when I had the chance to make another Human character, I jumped at the chance, confidant Jennifer Hale would make just as lovely a Smuggler as she did Commando.

…Except, my human smuggler didn't sound like Ms. Hale, as expected.

So my question: What determines the voice actor/actress for your character? It doesn't appear to be based on race – is it based on class? Body type? Something else entirely?