The tone or intonation of your voice is an important part of the body language. Not the words your pronounce, but the way you do it can tell alot about some one’s personality. And like body language, alot of people arent aware that their voice gives away alot of information.
Can you judge a person only by hearing their voice?
You all know the example of hearing a person for the first time on the telephone. Automatically you make an image of that person in your head, based on the voice you hear. If the person is a fast talker, then you see that person as self confident, because he isnt afraid to speak and knows to articulate well. Opposite of that is a person you really need to focus to hear them well, because they speak with a soft voice. In this case the person gives a shy, maybe scared impression.