How to configure the sound control keys

[MR]

My wonderful wireless multimedia keyboard just bit the dust, and all I
have as a substitute at the moment is a keyboard with no multimedia
keys.  I'd like to reconfigure the keys with combinations that will
let me control the volume anyway, but I can't find any such
keystrokes.  They're not in the keyboard settings or in the window
manager settings.

Where are these configured?

Thanks.

MR