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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!

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# How to plot frequency vs gain for a filter?

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