feat: add Gain Node

core/Gain.cpp

@@ -0,0 +1,17 @@
+#include "Gain.hpp"
+
+Gain::Gain(float init_gain) : gain_(init_gain) {}
+
+void Gain::process(const float *in, float *out, uint32_t frames) {
+  for (uint32_t i = 0; i < frames; ++i) {
+    out[i] = in[i] * gain_;
+  }
+}
+
+void Gain::processStereo(const float *inLeft, const float *inRight,
+                         float *outLeft, float *outRight, uint32_t frames) {
+  for (uint32_t i = 0; i < frames; ++i) {
+    outLeft[i] = inLeft[i] * gain_;
+    outRight[i] = inRight[i] * gain_;
+  }
+}

core/Gain.hpp

@@ -0,0 +1,24 @@
+#ifndef GAIN_HPP_INCLUDED
+#define GAIN_HPP_INCLUDED
+
+#include <cstdint>
+
+class Gain {
+public:
+  Gain(float init_gain = 1.0f);
+  // Process mono signal
+  void process(const float *in, float *out, uint32_t frames);
+
+  // Process stereo (two channels)
+  void processStereo(const float *inLeft, const float *inRight, float *outLeft,
+                     float *outRight, uint32_t frames);
+
+private:
+  float gain_;
+
+public:
+  void setGain(float g) { gain_ = g; }
+  float getGain() const { return gain_; }
+};
+
+#endif // GAIN_H__INCLUDED