From 3b1941038e512389cff5036ae4fb4d591ac28e79 Mon Sep 17 00:00:00 2001
From: KubaPro010 <kuba.pro010@gmail.com>
Date: Thu, 27 Mar 2025 18:53:49 +0100
Subject: [PATCH] some lpf changes

---
 lib/filters.c | 20 ++++++++++----------
 lib/filters.h | 20 ++++++++++----------
 src/fm95.c    |  2 +-
 3 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/lib/filters.c b/lib/filters.c
index 9dc0a32..e09a107 100644
--- a/lib/filters.c
+++ b/lib/filters.c
@@ -15,13 +15,13 @@ float hard_clip(float sample, float threshold) {
 	return fmaxf(-threshold, fminf(threshold, sample));
 }
 
-void init_lpf(FIR *filter, float cutoff, int sample_rate) {
+void init_lpf(LPFFilter *filter, float cutoff, int sample_rate) {
 	float a = tanf(M_PI*cutoff/sample_rate);
 	float a2 = a*a;
 	float r, e;
 
-	for(int i = 0; i < FIR_ORDER; i++) {
-		r = sinf(M_PI*(2.0f*i+1.0f)/(4.0f*FIR_ORDER));
+	for(int i = 0; i < LPF_ORDER; i++) {
+		r = sinf(M_PI*(2.0f*i+1.0f)/(4.0f*LPF_ORDER));
 		e = a2+2.0f*a*r+1.0f;
 		filter->A[i] = a2 / e;
 		filter->d1[i] = 2.0f*(1.0f-a2)/e;
@@ -29,13 +29,13 @@ void init_lpf(FIR *filter, float cutoff, int sample_rate) {
 	}
 }
 
-float process_lpf(FIR *filter, float x) {
-	float output;
-	for(int i = 0; i < FIR_ORDER; i++) {
-		filter->w0[i] = filter->d1[i]*filter->w1[i] + filter->d2[i]*filter->w2[i] + x;
-        output = filter->A[i] * (filter->w0[i] + 2.0f * filter->w1[i] + filter->w2[i]);
+float process_lpf(LPFFilter *filter, float x) {
+    float y = x;
+    for(int i = 0; i < LPF_ORDER; i++) {
+        filter->w0[i] = filter->d1[i] * filter->w1[i] + filter->d2[i] * filter->w2[i] + y;
+        y = filter->A[i] * (filter->w0[i] + 2.0f * filter->w1[i] + filter->w2[i]);
         filter->w2[i] = filter->w1[i];
         filter->w1[i] = filter->w0[i];
-	}
-	return output;
+    }
+    return y;
 }
\ No newline at end of file
diff --git a/lib/filters.h b/lib/filters.h
index 228b645..6712be8 100644
--- a/lib/filters.h
+++ b/lib/filters.h
@@ -5,7 +5,7 @@
 #include "constants.h"
 #include "oscillator.h"
 
-#define FIR_ORDER 5
+#define LPF_ORDER 5
 
 typedef struct
 {
@@ -21,12 +21,12 @@ float hard_clip(float sample, float threshold);
 
 typedef struct
 {
-	float A[FIR_ORDER];
-	float d1[FIR_ORDER];
-	float d2[FIR_ORDER];
-	float w0[FIR_ORDER];
-	float w1[FIR_ORDER];
-	float w2[FIR_ORDER];
-} FIR;
-void init_lpf(FIR *filter, float cutoff, int sample_rate);
-float process_lpf(FIR *filter, float x);
\ No newline at end of file
+	float A[LPF_ORDER];
+	float d1[LPF_ORDER];
+	float d2[LPF_ORDER];
+	float w0[LPF_ORDER];
+	float w1[LPF_ORDER];
+	float w2[LPF_ORDER];
+} LPFFilter;
+void init_lpf(LPFFilter *filter, float cutoff, int sample_rate);
+float process_lpf(LPFFilter *filter, float x);
\ No newline at end of file
diff --git a/src/fm95.c b/src/fm95.c
index 00c4512..c5db697 100644
--- a/src/fm95.c
+++ b/src/fm95.c
@@ -414,7 +414,7 @@ int main(int argc, char **argv) {
 	init_preemphasis(&preemp_l, preemphasis_tau, sample_rate);
 	init_preemphasis(&preemp_r, preemphasis_tau, sample_rate);
 
-	FIR lpf_l, lpf_r;
+	LPFFilter lpf_l, lpf_r;
 	init_lpf(&lpf_l, 15000, sample_rate);
 	init_lpf(&lpf_r, 15000, sample_rate);