radio95/fm95
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This commit is contained in:
KubaPro010
2024-12-31 11:53:58 +01:00
parent b0b2f2e4bc
commit 0d4a35817e
5 changed files with 261 additions and 10 deletions
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16
stereo_coder.c
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@@ -81,9 +81,9 @@ typedef struct {
float prev_sample;
} PreEmphasis;
void init_pre_emphasis(PreEmphasis *pe) {
void init_pre_emphasis(PreEmphasis *pe, float sample_rate) {
pe->prev_sample = 0.0f;
pe->alpha = exp(-1 / (PREEMPHASIS_TAU * SAMPLE_RATE));
pe->alpha = exp(-1 / (PREEMPHASIS_TAU * sample_rate));
}
float apply_pre_emphasis(PreEmphasis *pe, float sample) {
@@ -100,12 +100,12 @@ typedef struct {
int buffer_index;
} LowPassFilter;
void init_low_pass_filter(LowPassFilter *lp) {
void init_low_pass_filter(LowPassFilter *lp, float sample_rate) {
for (int i = 0; i < FIR_TAPS; i++) {
for (int j = 0; j < FIR_PHASES; j++) {
int mi = i * FIR_PHASES + j + 1;
float sincpos = mi - (((FIR_TAPS * FIR_PHASES) + 1.0f) / 2.0f);
float firlowpass = (sincpos == 0.0f) ? 1.0f : sinf(M_2PI * LPF_CUTOFF * sincpos / SAMPLE_RATE) / (PI * sincpos);
float firlowpass = (sincpos == 0.0f) ? 1.0f : sinf(M_2PI * LPF_CUTOFF * sincpos / sample_rate) / (PI * sincpos);
float window = 0.54f - 0.46f * cosf(M_2PI * mi / (FIR_TAPS * FIR_PHASES)); // Hamming window
lp->low_pass_fir[j][i] = firlowpass * window;
}
@@ -205,13 +205,13 @@ int main() {
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);
init_pre_emphasis(&preemp_l, SAMPLE_RATE);
init_pre_emphasis(&preemp_r, SAMPLE_RATE);
#endif
#ifdef LPF
LowPassFilter lpf_l, lpf_r;
init_low_pass_filter(&lpf_l);
init_low_pass_filter(&lpf_r);
init_low_pass_filter(&lpf_l, SAMPLE_RATE);
init_low_pass_filter(&lpf_r, SAMPLE_RATE);
#endif
signal(SIGINT, stop);