Hey Chris, 

Interesting question, never really thought about it.

The classification is really to help create acoustic models targeted to people with similar vocal characteristics.  We chose these two broad groupings because they reflect the the fact that men and women have different vocal fold sizes.  From Wikipedia:

The perceived pitch of a person's voice is determined by a number of different factors, not least of which is the fundamental frequency of the sound generated by the larynx. A person's natural fundamental frequency is influenced by many factors, including the length, size, and tension of the vocal folds. In an adult male, this frequency averages about 125 Hz, adult females around 210 Hz, in children the frequency is over 300 Hz.

Please classify yourself wherever your voice might fit into the two broad groupings we have chosen (i.e. male or female), or just leave it blank, and we can try to classify it.

I think the real issue might be whether I should be using the word "gender" or "sex" to distinguish these two groups.  Let me know if I should change this.

thanks for your interest in VoxForge,

Ken 

--- (Edited on 12/3/2007 11:02 am [GMT-0500] by kmaclean) ---