All the way through the interview you want to be able to maintain a constant and predictable manner in the way in which you answer questions. You do not want to be able to answer some questions immediately as if you are reciting a script because there will be times when you won't immediately know the answer. Every answer that you give should seem as if you have given it to a moment's thought and your delivery of that answer is natural and in keeping with your character.
Your tone of voice should remain constant and unexcited throughout the exchange of information your voice should be firm and warm well modulated and relaxed. Try to be conscious of not speaking too fast and becoming emotionally involved to such a degree that your speech and voice are affected. If you feel rushed during the interview, this will manifest itself in the way that you speak. By remaining calm your voice won't let you down and thus won't create unnecessary problems for you.