IIR Filter's Response : This Java applet analyzes IIR filter's frequency and In/Out characteristics.
Make some modification in the text box, then click "Read Coeffs" to draw frequency response. You can also get filtered output by "Read InWave" button. The filter consists of serialized four Biquad filters (see figure 1). The number of data is up to 100.
If this applet looks something weird, please reload it.
As to Biquad (2nd order IIR) filters, See fig. 1. Please be careful of the polarity of b1 and b2 are inverted on the actual design.
fig. 1. Mathematical model of Biquad (2nd order IIR filter)