For example, does the voltage level vary in a consistent manner,
In a consistent manor with what?
You need to do some research.
Have a look at some audio signals:-
https://www.google.co.uk/search?q=audio+signal&hl=en&client=firefox-a&hs=OCz&tbo=u&rls=org.mozilla:en-US:official&tbm=isch&source=univ&sa=X&ei=00LPUMWgMI600QWt1YCQCQ&ved=0CEYQsAQ&biw=1212&bih=747
You need to know what you want before anyone can tell you what to do.