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add preemphasis

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This commit is contained in:
KubaPro010
2024-12-30 16:45:28 +01:00
parent 58c725ed8e
commit 9688d98a2a
1 changed files with 42 additions and 5 deletions
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47
stereo_coder.c
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@@ -6,6 +6,11 @@
#include <signal.h>
#include <string.h>
// Features
// #define PREEMPHASIS
#define SAMPLE_RATE 192000 // Don't go lower than 108 KHz, becuase it (53000*2) and (38000+15000)
#define INPUT_DEVICE "real_real_tx_audio_input.monitor"
#define OUTPUT_DEVICE "alsa_output.platform-soc_sound.stereo-fallback"
#define BUFFER_SIZE 512
@@ -15,6 +20,10 @@
#define PILOT_VOLUME 0.02f // 19 KHz Pilot
#define STEREO_VOLUME 0.4f // L-R signal
#ifdef PREEMPHASIS
#define PREEMPHASIS_TAU 0.00005 // 50 microseconds, use 0.000075 if in america
#endif
volatile sig_atomic_t to_run = 1;
float clip(float sample) {
@@ -58,6 +67,21 @@ float get_next_sample(Oscillator *osc) {
return sample;
}
#ifdef PREEMPHASIS
typedef struct {
float prev_sample;
} PreEmphasis;
void init_pre_emphasis(PreEmphasis *pe) {
pe->prev_sample = 0.0f;
}
float apply_pre_emphasis(PreEmphasis *pe, float sample) {
float output = sample - pe->prev_sample * (1.0f - (1 - exp(-1.0 / (SAMPLE_RATE * PREEMPHASIS_TAU))));
pe->prev_sample = sample;
return output;
}
#endif
static void stop(int signum) {
(void)signum;
printf("\nReceived stop signal. Cleaning up...\n");
@@ -66,7 +90,6 @@ static void stop(int signum) {
int main() {
printf("STCode : Stereo encoder made by radio95 (with help of ChatGPT and Claude, thanks!)\n");
const float SAMPLE_RATE = 192000.0f; // Don't go lower than 108 KHz, becuase it (53000*2) and (38000+15000)
const float PILOT_FREQ = 19000.0f; // Don't touch this
const float STEREO_FREQ = 38000.0f; // This too
@@ -132,6 +155,11 @@ int main() {
Oscillator pilot_osc, stereo_osc;
init_oscillator(&pilot_osc, PILOT_FREQ, SAMPLE_RATE);
init_oscillator(&stereo_osc, STEREO_FREQ, SAMPLE_RATE);
#ifdef PREEMPHASIS
PreEmphasis preemp_l, preemp_r;
init_pre_emphasis(&preemp_l);
init_pre_emphasis(&preemp_r);
#endif
signal(SIGINT, stop);
signal(SIGTERM, stop);
@@ -149,12 +177,21 @@ int main() {
for (int i = 0; i < BUFFER_SIZE; i++) {
float pilot = get_next_sample(&pilot_osc);
float stereo_carrier = get_next_sample(&stereo_osc);
float l_in = left[i];
float r_in = right[i];
float current_left = clip(left[i]);
float current_right = clip(right[i]);
#ifdef PREEMPHASIS
float preemphasized_left = apply_pre_emphasis(&preemp_l, l_in);
float preemphasized_right = apply_pre_emphasis(&preemp_r, r_in);
float current_left_input = clip(preemphasized_left);
float current_right_input = clip(preemphasized_right);
#else
float current_left_input = clip(r_in);
float current_right_input = clip(r_in);
#endif
float mono = (current_left + current_right) / 2.0f;
float stereo = (current_left - current_right) / 2.0f;
float mono = (current_left_input + current_right_input) / 2.0f;
float stereo = (current_left_input - current_right_input) / 2.0f;
mpx[i] = mono * MONO_VOLUME +
pilot * PILOT_VOLUME +