iirj

An IIR filter library written in JAVA.

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

You can also calculate the filter coefficients with Python's scipy and then create your custom IIR filter. See the python-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].

Usage

import uk.me.berndporr.iirj.*;

Constructor

Butterworth butterworth = new Butterworth();

Initialisation

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);

Filtering

Sample by sample for realtime processing:

v = butterworth.filter(v)

Coding examples

See the *Test.java files for complete examples for all filter types. Run them with mvn test. These test programs write the different impulse responses of the filters to text files.

Installation

Local install

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

Maven central

At click on the iirj version number and then choose the appropriate installation option, for example for Android studio.

Android Studio

dependencies {
    implementation group: 'uk.me.berndporr', name:'iirj', version: '1.5'
}

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

Documentation

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

Testing

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

To see the impulse and frequency responses run:

python3 ./plot_impulse_fresponse.py <filter>

where is is bessel, butterworth, chebyshevI or chebyshevII.

The script DetectorTest uses a bandpass filter to detect the heartbeats of an ECG recording faking a matched filter which could be also seen as a 1st approximation of a wavelet. The heartrate is stored in hr.txt.

Have fun

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