[feat]: Filter (#18)

closes #16

Reviewed-on: #18

inc/Synth.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "ADSR.h"
+#include "Filter.h"
 #include "Adder.h"
 #include "Effect.h"
 #include "Note.h"
@@ -14,13 +15,14 @@ class Synth {
     std::vector<Oscillator*> m_oscillators;
     std::vector<Effect*> m_effects;
     std::vector<float> m_out_signal;
+    Oscillator* m_lfo;
     void zero_signal();
     void get_note();
     void trigger_note_on_effects();
     void untrigger_note_on_effects();
     void apply_effects();
     void add_oscillator();
-
+    void apply_filter_lfo();
   public:
     Synth(/* args */);
     ~Synth();
@@ -32,4 +34,6 @@ class Synth {
     const std::vector<Oscillator*>& GetOscillators() { return m_oscillators; }
     const bool& GetIsNoteTriggered() { return is_note_triggered; }
     ADSR* GetADSR() { return (ADSR*)m_effects[0]; }
+    Filter* GetFilter() { return (Filter*)m_effects[1]; }
+    void SetFilter(FilterType type);
 };