/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright (c) 2009 by Vinnie Falco
* Copyright (c) 2016 by Bernd Porr
*/
package uk.me.berndporr.iirj;
import org.apache.commons.math3.complex.Complex;
import org.apache.commons.math3.complex.ComplexUtils;
/**
* User facing class which contains all the methods the user uses
* to create Butterworth filters. This done in this way:
* Butterworth butterworth = new Butterworth();
* Then call one of the methods below to create
* low-,high-,band-, or stopband filters. For example:
* butterworth.bandPass(2,250,50,5);
*/
public class Butterworth extends Cascade {
class AnalogLowPass extends LayoutBase {
private int nPoles;
public AnalogLowPass(int _nPoles) {
super(_nPoles);
nPoles = _nPoles;
setNormal(0, 1);
}
public void design() {
reset();
double n2 = 2 * nPoles;
int pairs = nPoles / 2;
for (int i = 0; i < pairs; ++i) {
Complex c = ComplexUtils.polar2Complex(1F, Math.PI/2.0
+ (2 * i + 1) * Math.PI / n2);
addPoleZeroConjugatePairs(c, Complex.INF);
}
if ((nPoles & 1) == 1)
add(new Complex(-1), Complex.INF);
}
}
private void setupLowPass(int order, double sampleRate,
double cutoffFrequency, int directFormType) {
AnalogLowPass m_analogProto = new AnalogLowPass(order);
m_analogProto.design();
LayoutBase m_digitalProto = new LayoutBase(order);
new LowPassTransform(cutoffFrequency / sampleRate, m_digitalProto,
m_analogProto);
setLayout(m_digitalProto, directFormType);
}
/**
* Butterworth Lowpass filter with default topology
*
* @param order
* The order of the filter
* @param sampleRate
* The sampling rate of the system
* @param cutoffFrequency
* the cutoff frequency
*/
public void lowPass(int order, double sampleRate, double cutoffFrequency) {
setupLowPass(order, sampleRate, cutoffFrequency,
DirectFormAbstract.DIRECT_FORM_II);
}
/**
* Butterworth Lowpass filter with custom topology
*
* @param order
* The order of the filter
* @param sampleRate
* The sampling rate of the system
* @param cutoffFrequency
* The cutoff frequency
* @param directFormType
* The filter topology. This is either
* DirectFormAbstract.DIRECT_FORM_I or DIRECT_FORM_II
*/
public void lowPass(int order, double sampleRate, double cutoffFrequency,
int directFormType) {
setupLowPass(order, sampleRate, cutoffFrequency, directFormType);
}
private void setupHighPass(int order, double sampleRate,
double cutoffFrequency, int directFormType) {
AnalogLowPass m_analogProto = new AnalogLowPass(order);
m_analogProto.design();
LayoutBase m_digitalProto = new LayoutBase(order);
new HighPassTransform(cutoffFrequency / sampleRate, m_digitalProto,
m_analogProto);
setLayout(m_digitalProto, directFormType);
}
/**
* Highpass filter with custom topology
*
* @param order
* Filter order (ideally only even orders)
* @param sampleRate
* Sampling rate of the system
* @param cutoffFrequency
* Cutoff of the system
* @param directFormType
* The filter topology. See DirectFormAbstract.
*/
public void highPass(int order, double sampleRate, double cutoffFrequency,
int directFormType) {
setupHighPass(order, sampleRate, cutoffFrequency, directFormType);
}
/**
* Highpass filter with default filter topology
*
* @param order
* Filter order (ideally only even orders)
* @param sampleRate
* Sampling rate of the system
* @param cutoffFrequency
* Cutoff of the system
*/
public void highPass(int order, double sampleRate, double cutoffFrequency) {
setupHighPass(order, sampleRate, cutoffFrequency,
DirectFormAbstract.DIRECT_FORM_II);
}
private void setupBandStop(int order, double sampleRate,
double centerFrequency, double widthFrequency, int directFormType) {
AnalogLowPass m_analogProto = new AnalogLowPass(order);
m_analogProto.design();
LayoutBase m_digitalProto = new LayoutBase(order * 2);
new BandStopTransform(centerFrequency / sampleRate, widthFrequency
/ sampleRate, m_digitalProto, m_analogProto);
setLayout(m_digitalProto, directFormType);
}
/**
* Bandstop filter with default topology
*
* @param order
* Filter order (actual order is twice)
* @param sampleRate
* Samping rate of the system
* @param centerFrequency
* Center frequency
* @param widthFrequency
* Width of the notch
*/
public void bandStop(int order, double sampleRate, double centerFrequency,
double widthFrequency) {
setupBandStop(order, sampleRate, centerFrequency, widthFrequency,
DirectFormAbstract.DIRECT_FORM_II);
}
/**
* Bandstop filter with custom topology
*
* @param order
* Filter order (actual order is twice)
* @param sampleRate
* Samping rate of the system
* @param centerFrequency
* Center frequency
* @param widthFrequency
* Width of the notch
* @param directFormType
* The filter topology
*/
public void bandStop(int order, double sampleRate, double centerFrequency,
double widthFrequency, int directFormType) {
setupBandStop(order, sampleRate, centerFrequency, widthFrequency,
directFormType);
}
private void setupBandPass(int order, double sampleRate,
double centerFrequency, double widthFrequency, int directFormType) {
AnalogLowPass m_analogProto = new AnalogLowPass(order);
m_analogProto.design();
LayoutBase m_digitalProto = new LayoutBase(order * 2);
new BandPassTransform(centerFrequency / sampleRate, widthFrequency
/ sampleRate, m_digitalProto, m_analogProto);
setLayout(m_digitalProto, directFormType);
}
/**
* Bandpass filter with default topology
*
* @param order
* Filter order
* @param sampleRate
* Sampling rate
* @param centerFrequency
* Center frequency
* @param widthFrequency
* Width of the notch
*/
public void bandPass(int order, double sampleRate, double centerFrequency,
double widthFrequency) {
setupBandPass(order, sampleRate, centerFrequency, widthFrequency,
DirectFormAbstract.DIRECT_FORM_II);
}
/**
* Bandpass filter with custom topology
*
* @param order
* Filter order
* @param sampleRate
* Sampling rate
* @param centerFrequency
* Center frequency
* @param widthFrequency
* Width of the notch
* @param directFormType
* The filter topology (see DirectFormAbstract)
*/
public void bandPass(int order, double sampleRate, double centerFrequency,
double widthFrequency, int directFormType) {
setupBandPass(order, sampleRate, centerFrequency, widthFrequency,
directFormType);
}
}
