As with FIR filters, there are many different ways of designing IIRs filters as well. In the general case, IIR filter design is far more complex.

Fortunately, a guy named Robert Bristow-Johnson has come to our aid and wrote a document which allows 2nd order IIR filters to be designed using a 'cookbook' approach. This documant is in the public domain and can be found all over the net simply by searching for RBJ's name.

The RBJ equations were used to implement the filtering demo programs.

The demo programs are : low_pass_2 , high_pass_2 and parametric_eq .