start modularization

filter/iir.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <math.h>
+#include "../lib/constants.h"
+
+typedef struct
+{
+	float alpha;
+	float prev_sample;
+	float gain;
+} ResistorCapacitor;
+
+void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate, float ref_freq);
+float apply_preemphasis(ResistorCapacitor *filter, float sample);