[sdiy] Transfer Functions

[Stewart Pye]

With the talk of transfer functions of filter circuits I'm wondering if 
someone could point me to somewhere on the internet or a book that would 
help me to learn this...

I studied electronics (advanced diploma) at a technical college about 12 
years ago and do recall touching on this, but I'd have to re-learn the 
mathematics as I wasn't really interested in it at the time, however I 
did pass subjects that delt with imaginary numbers and such things. I 
just can't remember!. Until now I've usually been able to get by with 
things like f = 1/2*pi*R*C.

Cheers,
Stewart.