Where are footstep sounds?

I noticed that characters - humans and demihumans - make different sounds on different terrain. Some kinds use the same sounds, like hard floors and stone - gravel and pebbles. Where are those resources? How are they used? Perhaps I should patch avatars with better footsteps for terrain, if it's only a matter of not enough sound files.

And ogres stomp in the fog of war, but not when they appear on the scene. Their INI file has the field for footsteps sounds empty. Would be much better to hear those thundering footfalls during fights too.