From 58a37da27c71b7735125d58880d0809c599e2e4d Mon Sep 17 00:00:00 2001
From: KubaPro010 <kuba.pro010@gmail.com>
Date: Tue, 8 Jul 2025 23:04:38 +0200
Subject: [PATCH] clip bs412 and make it simpler to understand, both by me and
 the compiler

---
 filter/bs412.c | 10 +++++-----
 filter/bs412.h |  5 +++--
 src/fm95.c     |  4 ++--
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/filter/bs412.c b/filter/bs412.c
index 5232a1b..207ab2f 100644
--- a/filter/bs412.c
+++ b/filter/bs412.c
@@ -11,7 +11,8 @@ inline float deviation_to_dbr(float deviation) {
 	return 10.0f * (log2f(deviation) - LOG2_19000) * 0.30103f;
 }
 
-void init_bs412(BS412Compressor* mpx, float target_power, float attack, float release, int sample_rate) {
+void init_bs412(BS412Compressor* mpx, float mpx_deviation, float target_power, float attack, float release, int sample_rate) {
+	mpx->mpx_deviation = mpx_deviation;
 	mpx->sample_counter = 0;
 	mpx->sample = 0;
 	mpx->sample_rate = sample_rate;
@@ -24,8 +25,8 @@ void init_bs412(BS412Compressor* mpx, float target_power, float attack, float re
 	#endif
 }
 
-float bs412_compress(BS412Compressor* mpx, float deviation) {
-	mpx->sample += deviation * deviation; // rmS
+float bs412_compress(BS412Compressor* mpx, float sample) {
+	mpx->sample += sample * sample * mpx->mpx_deviation; // rmS
 	mpx->sample_counter++;
 
 	float inv_counter = 1.0f / mpx->sample_counter;
@@ -52,6 +53,5 @@ float bs412_compress(BS412Compressor* mpx, float deviation) {
 	else
 		mpx->gain = mpx->gain * mpx->release + (1.0f - mpx->release) * gain_target;
 
-
-	return deviation*mpx->gain;
+	return fminf(sample*mpx->gain, dbr_to_deviation(mpx->target*1.1f));
 }
diff --git a/filter/bs412.h b/filter/bs412.h
index 10985f8..ce3272f 100644
--- a/filter/bs412.h
+++ b/filter/bs412.h
@@ -11,6 +11,7 @@
 
 typedef struct
 {
+	int mpx_deviation;
 	int sample_counter;
 	int sample_rate;
 	float target;
@@ -23,5 +24,5 @@ typedef struct
 float dbr_to_deviation(float dbr);
 float deviation_to_dbr(float deviation);
 
-void init_bs412(BS412Compressor *mpx, float target_power, float attack, float release, int sample_rate);
-float bs412_compress(BS412Compressor *mpx, float deviation);
\ No newline at end of file
+void init_bs412(BS412Compressor *mpx, float mpx_deviation, float target_power, float attack, float release, int sample_rate);
+float bs412_compress(BS412Compressor *mpx, float sample);
\ No newline at end of file
diff --git a/src/fm95.c b/src/fm95.c
index 9685b76..a0f418d 100644
--- a/src/fm95.c
+++ b/src/fm95.c
@@ -167,7 +167,7 @@ int run_fm95(const FM95_Config config, FM95_Runtime* runtime) {
 	init_preemphasis(&preemp_r, config.preemphasis, config.sample_rate, config.preemp_unity_freq);
 
 	BS412Compressor bs412;
-	init_bs412(&bs412, config.mpx_power, config.bs412_attack, config.bs412_release, config.sample_rate);
+	init_bs412(&bs412, config.mpx_deviation, config.mpx_power, config.bs412_attack, config.bs412_release, config.sample_rate);
 
 	TiltCorrectionFilter tilter;
 	tilt_init(&tilter, config.tilt);
@@ -232,7 +232,7 @@ int run_fm95(const FM95_Config config, FM95_Runtime* runtime) {
 				}
 			}
 
-			mpx = bs412_compress(&bs412, mpx*config.mpx_deviation) / config.mpx_deviation;
+			mpx = bs412_compress(&bs412, mpx);
 			
 			output[i] = hard_clip(tilt(&tilter, (mpx_in[i]+mpx))*config.master_volume, 1.0); // Ensure peak deviation of 75 khz, assuming we're calibrated correctly (lower)
 			advance_oscillator(&osc);