From fad95b6bab27d9911c3142e4a5f06b88a49f4d19 Mon Sep 17 00:00:00 2001
From: beirich <beirich@4bbf4f03-6f44-549e-7e59-35d4b0962838>
Date: Sat, 21 Apr 2012 20:22:13 +0000
Subject: [PATCH] Add 3-band equalizer. Not hooked up to client for time being
 though. Maybe later I'll expand it to more bands and create presets. Just
 wanted to check it in for now.

---
 .../Sound/Utilities/Equalizer.cs              | 98 +++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 BizHawk.Emulation/Sound/Utilities/Equalizer.cs

diff --git a/BizHawk.Emulation/Sound/Utilities/Equalizer.cs b/BizHawk.Emulation/Sound/Utilities/Equalizer.cs
new file mode 100644
index 0000000000..ae30719242
--- /dev/null
+++ b/BizHawk.Emulation/Sound/Utilities/Equalizer.cs
@@ -0,0 +1,98 @@
+// C# port of C-based 3-band equalizer (C) Neil C / Etanza Systems / 2006
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Sound
+{
+    public sealed class Equalizer
+    {
+        double lowFilter;
+        double lowFilterPole0;
+        double lowFilterPole1;
+        double lowFilterPole2;
+        double lowFilterPole3;
+
+        double highFilter;
+        double highFilterPole0;
+        double highFilterPole1;
+        double highFilterPole2;
+        double highFilterPole3;
+
+        double sampleDataMinus1;
+        double sampleDataMinus2;
+        double sampleDataMinus3;
+
+        double lowGain;
+        double midGain;
+        double highGain;
+        
+        const double sampleRate = 44100.0;
+        const double verySmallAmount = (1.0 / 4294967295.0);
+
+        double lowfreq;
+        public double LowFreqCutoff 
+        {
+            get { return lowfreq; }
+            set
+            {
+                lowfreq = value;
+                lowFilter = 2 * Math.Sin(Math.PI * (lowfreq / sampleRate));
+            }
+        }
+
+        double highfreq;
+        public double HighFreqCutoff
+        {
+            get { return highfreq; }
+            set
+            {
+                highfreq = value;
+                highFilter = 2 * Math.Sin(Math.PI * (highfreq / sampleRate));
+            }
+        }
+
+        public Equalizer(double lowFreq=880, double highFreq=5000)
+        {
+            lowGain = 1.3;
+            midGain = 0.9;
+            highGain = 1.3;
+            LowFreqCutoff = lowFreq;
+            HighFreqCutoff = highFreq;
+        }
+
+        public short EqualizeSample(short sample)
+        {
+            lowFilterPole0 += (lowFilter * (sample - lowFilterPole0)) + verySmallAmount;
+            lowFilterPole1 += lowFilter * (lowFilterPole0 - lowFilterPole1);
+            lowFilterPole2 += lowFilter * (lowFilterPole1 - lowFilterPole2);
+            lowFilterPole3 += lowFilter * (lowFilterPole2 - lowFilterPole3);
+            double l = lowFilterPole3;
+
+            highFilterPole0 += (highFilter * (sample - highFilterPole0)) + verySmallAmount;
+            highFilterPole1 += highFilter * (highFilterPole0 - highFilterPole1);
+            highFilterPole2 += highFilter * (highFilterPole1 - highFilterPole2);
+            highFilterPole3 += highFilter * (highFilterPole2 - highFilterPole3);
+            double h = sampleDataMinus3 - highFilterPole3;
+
+            double m = sample - (h + l);
+            l *= lowGain;
+            m *= midGain;
+            h *= highGain;
+
+            sampleDataMinus3 = sampleDataMinus2;
+            sampleDataMinus2 = sampleDataMinus1;
+            sampleDataMinus1 = sample;
+
+            return (short) (l + m + h);
+        }
+
+        public void Equalize(short[] samples)
+        {
+            for (int i = 0; i < samples.Length; i++)
+                samples[i] = EqualizeSample(samples[i]);
+        }
+    }
+}
\ No newline at end of file