Add brickwall limiter FX section

Source/DSP/Limiter.h

@@ -0,0 +1,44 @@
+#pragma once
+#include <cmath>
+#include <algorithm>
+
+class Limiter {
+public:
+    void prepare(double sr) {
+        sampleRate = sr;
+        envelope = 0.0f;
+    }
+
+    void setParameters(float threshold, float ceiling, float releaseMs) {
+        thresholdGain = threshold;
+        ceilingGain = ceiling;
+        releaseCoeff = std::exp(-1.0f / (std::max(releaseMs, 1.0f) * 0.001f * static_cast<float>(sampleRate)));
+        dryWet = 1.0f;
+    }
+
+    float process(float input) {
+        float absIn = std::abs(input);
+        if (absIn > envelope)
+            envelope = absIn;
+        else
+            envelope = releaseCoeff * envelope + (1.0f - releaseCoeff) * absIn;
+
+        float target = std::max(thresholdGain, ceilingGain);
+        float gain = 1.0f;
+        if (envelope > target && envelope > 1e-6f) {
+            float desired = target / envelope;
+            gain = std::min(1.0f, desired);
+        }
+
+        float wet = input * gain;
+        return input + (wet - input) * dryWet;
+    }
+
+private:
+    double sampleRate = 44100.0;
+    float thresholdGain = 1.0f;
+    float ceilingGain = 1.0f;
+    float releaseCoeff = 0.0f;
+    float dryWet = 1.0f;
+    float envelope = 0.0f;
+};