DIY Baxandall network

substitute 2*pi*f (frequency, in Hertz) for s and you should be able to move ahead.

If you are concerned with phase, also, you can substitute j*2*pi*f.

j is defined equal to the square-root of -1. Essentially it represents a 90 degree phase angle, where -1 would equal a full 180 degree phase angle.

Without taking everyone through a 2nd or 3rd year Electrical Engineering course, that is as short a summary as I can muster. :)