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package com.cyngn.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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