Implement fade in to prevent Triple Osc from clicking (#5199)

include/Instrument.h

@@ -132,6 +132,9 @@ public:
 
 
 protected:
+	// fade in to prevent clicks
+	void applyFadeIn(sampleFrame * buf, NotePlayHandle * n);
+
 	// instruments may use this to apply a soft fade out at the end of
 	// notes - method does this only if really less or equal
 	// desiredReleaseFrames() frames are left

include/NotePlayHandle.h

@@ -49,6 +49,9 @@ public:
 	void * m_pluginData;
 	std::unique_ptr<BasicFilters<>> m_filter;
 
+	// length of the declicking fade in
+	fpp_t m_fadeInLength;
+
 	// specifies origin of NotePlayHandle
 	enum Origins
 	{