Common -> Models

RedBookPlayer.Models/Hardware/DeEmphasisFilter.cs

@@ -0,0 +1,48 @@
+using System;
+using NWaves.Filters.BiQuad;
+
+namespace RedBookPlayer.Models.Hardware
+{
+    /// <summary>
+    /// Filter for applying de-emphasis to audio
+    /// </summary>
+    public class DeEmphasisFilter : BiQuadFilter
+    {
+        private static readonly double B0;
+        private static readonly double B1;
+        private static readonly double B2;
+        private static readonly double A0;
+        private static readonly double A1;
+        private static readonly double A2;
+
+        static DeEmphasisFilter()
+        {
+            double fc    = 5277;
+            double slope = 0.4850;
+            double gain  = -9.465;
+
+            double w0    = 2 * Math.PI * fc / 44100;
+            double A     = Math.Exp(gain / 40 * Math.Log(10));
+            double alpha = Math.Sin(w0) / 2 * Math.Sqrt(((A + (1 / A)) * ((1 / slope) - 1)) + 2);
+
+            double cs = Math.Cos(w0);
+            double v  = 2 * Math.Sqrt(A) * alpha;
+
+            B0 = A  * (A                          + 1 + ((A - 1) * cs) + v);
+            B1 = -2 * A * (A - 1                  + ((A     + 1) * cs));
+            B2 = A  * (A     + 1 + ((A - 1) * cs) - v);
+            A0 = A                                + 1 - ((A - 1) * cs) + v;
+            A1 = 2 * (A                           - 1 - ((A + 1) * cs));
+            A2 = A + 1 - ((A - 1) * cs) - v;
+
+            B2 /= A0;
+            B1 /= A0;
+            B0 /= A0;
+            A2 /= A0;
+            A1 /= A0;
+            A0 =  1;
+        }
+
+        public DeEmphasisFilter() : base(B0, B1, B2, A0, A1, A2) {}
+    }
+}