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An IIR filter library written in JAVA.

Highpass, lowpass, bandpass and bandstop asButterworth, Bessel and Chebyshev Type I/II.

You can also calculate the filter coefficients with Python'sscipy and then create your custom IIR filter.See thepython-design subdirectory.

It's based on the IIR1 library [https://github.com/berndporr/iir1]which in turn is based on Vinnie Falco's DSPFilters [https://github.com/vinniefalco/DSPFilters].

import uk.me.berndporr.iirj.*;

Butterworth butterworth = new Butterworth();

1. Bandstop

   butterworth.bandStop(order,Samplingfreq,Center freq,Width in frequ);

2. Bandpass

   butterworth.bandPass(order,Samplingfreq,Center freq,Width in frequ);

3. Lowpass

   butterworth.lowPass(order,Samplingfreq,Cutoff frequ);

4. Highpass

   butterworth.highPass(order,Samplingfreq,Cutoff frequ);

Sample by sample for realtime processing:

v = butterworth.filter(v)

See the*Test.java files for complete examplesfor all filter types. Run them withmvn test. These test programswrite the different impulse responses of the filters to text files.

• Clone this repository
• Runmvn install to add it to your local maven respository

Atclick on the iirj version number and then choose the appropriate installation option, forexample for Android studio.

dependencies {    implementation group: 'uk.me.berndporr', name:'iirj', version: '1.7'}

Android studio will automatically notify you if a new IIR library is available.

• Online:https://berndporr.github.io/iirj/
• mvn javadoc:javadoc generates the JavaDocs
• mvn site generates the web pages containing the documentationundertarget/site describing all commands in detail.

mvn test creates impulse responses in the subdirectoriesfor the different filters:target/surefire-reports.

To see the impulse and frequency responses run:

python3 ./plot_impulse_fresponse.py <filter>

where is is butterworth, bessel, chebyshevI or chebyshevII.

The script DetectorTest uses a bandpass filter to detect theheartbeats of an ECG recording faking a matched filter which couldbe also seen as a 1st approximation of a wavelet. The heartrate isstored in hr.txt.

Have fun

/Bernd Porr[http://www.berndporr.me.uk]