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/*
* Copyright (C) 2016 The CyanogenMod Project
*
* Licensed 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.
*/
package org.cyanogenmod.audiofx.widget;
/**
* Evaluate transfer functions of biquad filters in direct form 1.
*
* @author alankila
*/
public class Biquad {
private Complex mB0, mB1, mB2, mA0, mA1, mA2;
public void setHighShelf(double centerFrequency, double samplingFrequency,
double dbGain, double slope) {
double w0 = 2 * Math.PI * centerFrequency / samplingFrequency;
double a = Math.pow(10, dbGain/40);
double alpha = Math.sin(w0) / 2 * Math.sqrt((a + 1 / a) * (1 / slope - 1) + 2);
mB0 = new Complex(a*((a+1) + (a-1) *Math.cos(w0) + 2*Math.sqrt(a)*alpha), 0);
mB1 = new Complex(-2*a*((a-1) + (a+1)*Math.cos(w0)), 0);
mB2 = new Complex(a*((a+1) + (a-1) *Math.cos(w0) - 2*Math.sqrt(a)*alpha), 0);
mA0 = new Complex((a+1) - (a-1) *Math.cos(w0) + 2*Math.sqrt(a)*alpha, 0);
mA1 = new Complex(2*((a-1) - (a+1) *Math.cos(w0)), 0);
mA2 = new Complex((a+1) - (a-1) *Math.cos(w0) - 2*Math.sqrt(a)*alpha, 0);
}
public Complex evaluateTransfer(Complex z) {
Complex zSquared = z.mul(z);
Complex nom = mB0.add(mB1.div(z)).add(mB2.div(zSquared));
Complex den = mA0.add(mA1.div(z)).add(mA2.div(zSquared));
return nom.div(den);
}
}
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