This is really fascinating:
Scientists used to consider the frequency band of 500 hertz and below in the human voice as meaningless noise, because when a voice is filtered, removing all higher frequencies, ne hears nothing but a low-pitched hum. All words are lost. But then it was found that this low hum is an unconscious social instrument. It is different for each person, but in the course of a conversation people tend to converge. They settle on a single hum, and it is always the lower status person who does the adjusting. This was first demonstrated in an analysis of the Larry King Live television show. The host, Larry King, would adjust his timbre to that of high-ranking guests, like Mike Wallace or Elizabeth Taylor. Low-ranking guests, on the other hand, would adjust their timbre to that of King. The clearest adjustment to King's voice, indicating lack of confidence, came from former Vice President Dan Quayle.
The same spectral analysis has been applied to televised debates between U.S. presidential candidates. In all eight elections between 1960 and 2000 the popular vote matched the voice analysis: the majority of people voted for the candidate who held his own timbre rather than the one who adjusted.
From this site.