Java IIR Filter Designer is a Java library for designing Infinite Impulse Response (IIR) filters.

The implementation of this library is based on Scipy signal package.

Designing an IIR filter boils down to using the IIRDesigner's designDigitalFilter method. For example:

FilterCoefficients coefficients = IIRDesigner.designDigitalFilter(ApproximationFunctionType.BUTTERWORTH, FilterType.LOWPASS, new double[]{10.0}, new double[]{20.0}, 3.0, 40.0, 256.0);

The designDigitalFilter uses the following parameters:

1. ApproximationFunctionType approximationFunctionType - allowed types available in the ApproximationFunctionType enumerator (BUTTERWORTH, CHEBYSHEV1, CHEBYSHEV2, ELLIPTIC).
2. FilterType filterType - allowed values available in the FilterType enumerator (LOWPASS, HIGHPASS, BANDPASS, BANDSTOP).
3. double[] passbandEdgeFrequencies - contains an array of passband edge frequencies. In case of low-pass or high-pass filter the array should contain only one number, in case of band-pass or band-stop filters two numbers are required.
4. double[] stopbandEdgeFrequencies - contains an array of stopband edge frequencies.
5. double passbandRipple - describes what is the allowable ripple in the passband (in dB).
6. double stopbandAttenuation - describes how much attenuation is required in the stopband (dB).
7. double samplingFrequency - sampling frequency of the signal in Hz.