1 files changed, 46 insertions, 0 deletions
diff --git a/src/org/cyanogenmod/audiofx/widget/Biquad.java b/src/org/cyanogenmod/audiofx/widget/Biquad.java
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+++ b/src/org/cyanogenmod/audiofx/widget/Biquad.java
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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);
+    }
+}