Add Butterworth filter, rename the other filter

ProjectObsidian/Components/Audio/ButterworthFilter.cs

@@ -0,0 +1,142 @@
+using System;
+using FrooxEngine;
+using Elements.Assets;
+
+namespace Obsidian.Components.Audio;
+
+[Category(new string[] { "Audio" })]
+public class ButterworthFilter : Component, IAudioSource, IWorldElement
+{
+    [Range(0f, 10000f, "0.00")]
+    public readonly Sync<float> Frequency;
+
+    [Range(0.1f, 1.41f, "0.00")]
+    public readonly Sync<float> Resonance;
+
+    public readonly Sync<bool> LowPass;
+
+    public readonly SyncRef<IAudioSource> Source;
+
+    private double lastTime;
+
+    public bool IsActive
+    {
+        get
+        {
+            return Source.Target != null && Source.Target.IsActive;
+        }
+    }
+
+    protected override void OnAwake()
+    {
+        base.OnAwake();
+        lastTime = -1;
+    }
+
+    public int ChannelCount => Source.Target?.ChannelCount ?? 0;
+
+    public void Read<S>(Span<S> buffer) where S : unmanaged, IAudioSample<S>
+    {
+        if (!IsActive)
+        {
+            return;
+        }
+
+        Span<S> span = stackalloc S[buffer.Length];
+
+        span = buffer;
+
+        Source.Target.Read(span);
+
+        var filter = new FilterButterworth<S>(Frequency, (int)(span.Length / (Engine.Current.AudioSystem.DSPTime - lastTime)), LowPass ? FilterButterworth<S>.PassType.Lowpass : FilterButterworth<S>.PassType.Highpass, Resonance);
+
+        for (int i = 0; i < span.Length; i++)
+        {
+            filter.Update(ref span[i]);
+        }
+
+        lastTime = Engine.Current.AudioSystem.DSPTime;
+    }
+
+    public class FilterButterworth<S> where S: unmanaged, IAudioSample<S>
+    {
+        /// <summary>
+        /// rez amount, from sqrt(2) to ~ 0.1
+        /// </summary>
+        private readonly float resonance;
+
+        private readonly float frequency;
+        private readonly int sampleRate;
+        private readonly PassType passType;
+
+        private readonly float c, a1, a2, a3, b1, b2;
+
+        /// <summary>
+        /// Array of input values, latest are in front
+        /// </summary>
+        private S[] inputHistory = new S[2];
+
+        /// <summary>
+        /// Array of output values, latest are in front
+        /// </summary>
+        private S[] outputHistory = new S[3];
+
+        public FilterButterworth(float frequency, int sampleRate, PassType passType, float resonance)
+        {
+            this.resonance = resonance;
+            this.frequency = frequency;
+            this.sampleRate = sampleRate;
+            this.passType = passType;
+
+            switch (passType)
+            {
+                case PassType.Lowpass:
+                    c = 1.0f / (float)Math.Tan(Math.PI * frequency / sampleRate);
+                    a1 = 1.0f / (1.0f + resonance * c + c * c);
+                    a2 = 2f * a1;
+                    a3 = a1;
+                    b1 = 2.0f * (1.0f - c * c) * a1;
+                    b2 = (1.0f - resonance * c + c * c) * a1;
+                    break;
+                case PassType.Highpass:
+                    c = (float)Math.Tan(Math.PI * frequency / sampleRate);
+                    a1 = 1.0f / (1.0f + resonance * c + c * c);
+                    a2 = -2f * a1;
+                    a3 = a1;
+                    b1 = 2.0f * (c * c - 1.0f) * a1;
+                    b2 = (1.0f - resonance * c + c * c) * a1;
+                    break;
+            }
+        }
+
+        public enum PassType
+        {
+            Highpass,
+            Lowpass,
+        }
+
+        public void Update(ref S newInput)
+        {
+            S first = newInput.Multiply(a1);
+            S second = this.inputHistory[0].Multiply(a2);
+            S third = this.inputHistory[1].Multiply(a3);
+            S fourth = this.outputHistory[0].Multiply(b1);
+            S fifth = this.outputHistory[1].Multiply(b2);
+            S final = first.Add(second).Add(third).Subtract(fourth).Subtract(fifth);
+
+            this.inputHistory[1] = this.inputHistory[0];
+            this.inputHistory[0] = newInput;
+
+            this.outputHistory[2] = this.outputHistory[1];
+            this.outputHistory[1] = this.outputHistory[0];
+            this.outputHistory[0] = final;
+
+            newInput = final;
+        }
+
+        public S Value
+        {
+            get { return this.outputHistory[0]; }
+        }
+    }
+}

ProjectObsidian/Components/Audio/AudioLowPassFilter.cs → ProjectObsidian/Components/Audio/EMA_IIR_SmoothSignal.cs

@@ -5,7 +5,7 @@
 namespace Obsidian.Components.Audio;
 
 [Category(new string[] { "Audio" })]
-public class AudioLowPassFilter : Component, IAudioSource, IWorldElement
+public class EMA_IIR_SmoothSignal : Component, IAudioSource, IWorldElement
 {
     [Range(0f, 1f, "0.00")]
     public readonly Sync<float> SmoothingFactor;