[feat]: Oscillator fine-tune (#22)

closes #19

Reviewed-on: #22

inc/LFO.h

@@ -0,0 +1,20 @@
+#pragma once
+#include "Oscillator.h"
+
+class LFO: public Oscillator
+{
+private:
+    /* data */
+public:
+    LFO(/* args */);
+    ~LFO();
+    void SetFreq(float freq) { m_phase_dt = (this->*m_dt_function)(freq); }
+};
+
+LFO::LFO(/* args */): Oscillator(Sine, 0.f, 0.5f)
+{
+}
+
+LFO::~LFO()
+{
+}