Update iir.c

filter/iir.c

@@ -16,17 +16,26 @@ inline float apply_preemphasis(ResistorCapacitor *filter, float sample) {
 }
 
 void tilt_init(TiltCorrectionFilter* filter, float alpha) {
-    filter->alpha = alpha;  // 0.95 to 0.99 typically
+    // Leaky integrator for DC estimation: dc[n] = alpha*dc[n-1] + (1-alpha)*x[n]
-    filter->x_prev = 0.0f;
+    // Tilt correction: y[n] = x[n] - dc[n]
-    filter->y_prev = 0.0f;
+    
+    if (correction_strength >= 1.0f) {
+        correction_strength = 0.99999f;
+    }
+    if (correction_strength < 0.0f) {
+        correction_strength = 0.0f;
+    }
+    
+    filter->alpha = alpha;  // Leaky integrator coefficient
+    filter->dc_estimate = 0.0f;          // Running DC estimate
 }
 
-float tilt(TiltCorrectionFilter* filter, float input) {
+float tilt_correct(TiltCorrectionFilter* filter, float input) {
-    // High-pass: y[n] = α*y[n-1] + (x[n] - x[n-1])
+    // Update DC estimate using leaky integrator
-    float output = filter->alpha * filter->y_prev + (input - filter->x_prev);
+    filter->dc_estimate = filter->alpha * filter->dc_estimate + (1.0f - filter->alpha) * input;
     
-    filter->x_prev = input;
+    // Remove estimated DC component
-    filter->y_prev = output;
+    float output = input - filter->dc_estimate;
     
     return output;
 }