turn lpf and emphasis into a common rc

.vscode/.server-controller-port.log

@@ -1,5 +1,5 @@
 {
   "port": 13452,
-  "time": 1735989625302,
+  "time": 1737462229390,
   "version": "0.0.3"
 }

.vscode/settings.json

@@ -9,6 +9,8 @@
         "stdlib.h": "c",
         "error.h": "c",
         "math.h": "c",
-        "options.h": "c"
+        "options.h": "c",
+        "random": "c",
+        "__locale": "c"
     }
 }

lib/filters.c

@@ -1,25 +1,23 @@
 #include "filters.h"
 
-void init_emphasis(Emphasis *pe, float tau, float sample_rate) {
+void init_rc(ResistorCapacitor *rc, float tau, float sample_rate) {
-    pe->prev_sample = 0.0f;
+    rc->prev_sample = 0.0f;
-    pe->alpha = exp(-1 / (tau * sample_rate));
+    rc->alpha = exp(-1 / (tau * sample_rate));
 }
 
-float apply_pre_emphasis(Emphasis *pe, float sample) {
+float apply_pre_emphasis(ResistorCapacitor *rc, float sample) {
-    float audio = sample-pe->alpha*pe->prev_sample;
+    float audio = sample-rc->alpha*rc->prev_sample;
-    pe->prev_sample = audio;
+    rc->prev_sample = audio;
     return audio*2;
 }
 
-void init_low_pass_filter(LowPassFilter *lp, float cutoff_frequency, float sample_rate) {
+void init_low_pass_filter(ResistorCapacitor *rc, float cutoff_frequency, float sample_rate) {
-    float rc = 1/(M_2PI*cutoff_frequency);
+    init_rc(&rc, (-1 / (sample_rate * log(sample_rate/(sample_rate+(1/(M_2PI*cutoff_frequency)))))), sample_rate);
-    lp->alpha = sample_rate/(sample_rate+rc);
-    lp->prev_sample = 0.0f;
 }
 
-float apply_low_pass_filter(LowPassFilter *lp, float sample) {
+float apply_low_pass_filter(ResistorCapacitor *rc, float sample) {
-    float output = lp->alpha*sample+(1-lp->alpha)*lp->prev_sample;
+    float output = rc->alpha*sample+(1-rc->alpha)*rc->prev_sample;
-    lp->prev_sample = output;
+    rc->prev_sample = output;
     return output;
 }
 

lib/filters.h

@@ -11,18 +11,13 @@
 typedef struct {
     float alpha;
     float prev_sample;
-} Emphasis;
+} ResistorCapacitor; 
 
-void init_emphasis(Emphasis *pe, float tau, float sample_rate);
+void init_rc(ResistorCapacitor *pe, float tau, float sample_rate);
-float apply_pre_emphasis(Emphasis *pe, float sample);
+float apply_pre_emphasis(ResistorCapacitor *pe, float sample);
 
-typedef struct {
+void init_low_pass_filter(ResistorCapacitor *lp, float cutoff_frequency, float sample_rate);
-    float alpha;
+float apply_low_pass_filter(ResistorCapacitor *lp, float sample);
-    float prev_sample;
-} LowPassFilter;
-
-void init_low_pass_filter(LowPassFilter *lp, float cutoff_frequency, float sample_rate);
-float apply_low_pass_filter(LowPassFilter *lp, float sample);
 
 
 typedef struct {

src/crosby_stereo_coder.c

@@ -122,9 +122,9 @@ int main() {
     Oscillator osc;
     init_oscillator(&osc, 50000.0, SAMPLE_RATE);
 #ifdef PREEMPHASIS
-    Emphasis preemp_l, preemp_r;
+    ResistorCapacitor preemp_l, preemp_r;
-    init_emphasis(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
-    init_emphasis(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf_l, lpf_r;

src/mono_passthrough.c

@@ -104,8 +104,8 @@ int main() {
     }
 
 #ifdef PREEMPHASIS
-    Emphasis preemp;
+    ResistorCapacitor preemp;
-    init_emphasis(&preemp, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf;

src/options.h

@@ -1,4 +1,4 @@
-// #define PREEMPHASIS
+#define PREEMPHASIS
 // #define LPF
 
 #define buffer_maxlength 12288

src/polar_stereo_coder.c

@@ -121,9 +121,9 @@ int main() {
     Oscillator stereo_osc;
     init_oscillator(&stereo_osc, 31250.0, SAMPLE_RATE);
 #ifdef PREEMPHASIS
-    Emphasis preemp_l, preemp_r;
+    ResistorCapacitor preemp_l, preemp_r;
-    init_emphasis(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
-    init_emphasis(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf_l, lpf_r;

src/sca_mod.c

@@ -112,8 +112,8 @@ int main() {
     FMModulator mod;
     init_fm_modulator(&mod, FREQUENCY, DEVIATION, SAMPLE_RATE);
 #ifdef PREEMPHASIS
-    Emphasis preemp;
+    ResistorCapacitor preemp;
-    init_emphasis(&preemp, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf;

src/ssb_stereo_coder.c

@@ -128,9 +128,9 @@ int main() {
     DelayLine monoDelay;
     init_delay_line(&monoDelay, 99);
 #ifdef PREEMPHASIS
-    Emphasis preemp_l, preemp_r;
+    ResistorCapacitor preemp_l, preemp_r;
-    init_emphasis(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
-    init_emphasis(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf_l, lpf_r;

src/stereo_coder.c

@@ -122,9 +122,9 @@ int main() {
     Oscillator pilot_osc;
     init_oscillator(&pilot_osc, 19000.0, SAMPLE_RATE); // Pilot, it's there to indicate stereo and as a refrence signal with the stereo carrier
 #ifdef PREEMPHASIS
-    Emphasis preemp_l, preemp_r;
+    ResistorCapacitor preemp_l, preemp_r;
-    init_emphasis(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
-    init_emphasis(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf_l, lpf_r;

src/stereo_sca_mod.c

@@ -124,9 +124,9 @@ int main() {
     init_fm_modulator(&mod_mono, 67000, 6000, SAMPLE_RATE);
     init_fm_modulator(&mod_stereo, 80000, 6000, SAMPLE_RATE);
 #ifdef PREEMPHASIS
-    Emphasis preemp_l, preemp_r;
+    ResistorCapacitor preemp_l, preemp_r;
-    init_emphasis(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_l, PREEMPHASIS_TAU, SAMPLE_RATE);
-    init_emphasis(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
+    init_rc(&preemp_r, PREEMPHASIS_TAU, SAMPLE_RATE);
 #endif
 #ifdef LPF
     LowPassFilter lpf_l, lpf_r;