Java tutorial
/* * 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; /** * Transforms from an analogue lowpass filter to a digital lowpass filter */ public class LowPassTransform { private double f; private Complex transform(Complex c) { if (c.isInfinite()) return new Complex(-1, 0); // frequency transform c = c.multiply(f); Complex one = new Complex(1, 0); // bilinear low pass transform return (one.add(c)).divide(one.subtract(c)); } public LowPassTransform(double fc, LayoutBase digital, LayoutBase analog) { digital.reset(); // prewarp f = Math.tan(Math.PI * fc); int numPoles = analog.getNumPoles(); int pairs = numPoles / 2; for (int i = 0; i < pairs; ++i) { PoleZeroPair pair = analog.getPair(i); digital.addPoleZeroConjugatePairs(transform(pair.poles.first), transform(pair.zeros.first)); } if ((numPoles & 1) == 1) { PoleZeroPair pair = analog.getPair(pairs); digital.add(transform(pair.poles.first), transform(pair.zeros.first)); } digital.setNormal(analog.getNormalW(), analog.getNormalGain()); } }