Hello, I am trying to understand how this graph http://en.wikipedia.org/wiki/File:Bandwidth_2.svg gets plotted. My goal is to write a small program that takes the center frequency/bandwidth and a (cut/boost) gain values and plot the curve. I initially assumed, all I needed to find was an equation of gain in terms of frequency to plot it. I have been searching for a few weeks now and I keep running into transfer functions and many different types of them. But I dont understand how this translates into a gain(yaxis) vs freq(xaxis) plot. For example, I found the following equation at http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt b0 + b1*z^-1 + b2*z^-2 H(z) = ------------------------ (Eq 1) a0 + a1*z^-1 + a2*z^-2 the a0,a1,a2,b0,b1,b2 are calculated in terms of frequency/gain/bandwidth. On plotting H(z) I get something that looks like a bandpass filter curve but what does H(z) and z represent? I dont have an electrical engineering/math background but am really interested in understanding how this bandpass curve gets drawn. Any advice on how to go about this would be greatly appreciated. Thanks!