Add 'aweight.h'

aweight.h

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+/**
+ * aweight.h - Efficient A-weighting algorithm
+ * Copyright (C) 2024  Clyne Sullivan <clyne@bitgloo.com>
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef AWEIGHT_H
+#define AWEIGHT_H
+
+/**
+ * Applies A-weighting to the given audio sample.
+ * @param in_div4 The audio sample divided by four
+ * @return The filtered (A-weighted) sample
+ */
+inline float process(float in_div4)
+{
+    static float z1 = 0, z2 = 0, z3 = 0, z5 = 0;
+
+    float out1 = in_div4 + z1;
+    z1 = 1.062f * out1 + z2;
+    z2 = -0.14f * out1 - in_div4;
+
+    float out2 = out1 + z3;
+    z3 = out1;
+
+    float out3 = out2 + z5;
+    z5 = 0.985f * out3 - out2;
+
+    return out3;
+}
+
+#endif // AWEIGHT_H