radio95/fm95
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Code Issues Activity

try to add a simple rc lpf

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This commit is contained in:
KubaPro010
2025-03-26 14:04:38 +01:00
parent 4c472c0fc0
commit fc9bbd3262
3 changed files with 22 additions and 1 deletions
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12
lib/filters.c
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@@ -13,3 +13,15 @@ float apply_preemphasis(ResistorCapacitor *filter, float sample) {
float hard_clip(float sample, float threshold) {
return fmaxf(-threshold, fminf(threshold, sample));
}
void init_rc_lpf(ResistorCapacitor *filter, float cutoff, float sample_rate) {
filter->prev_sample = 0.0f;
float dt = 1.0f/sample_rate;
float rc = 1.0f/(cutoff*M_2PI);
filter->alpha = dt/(rc+dt);
}
float apply_rc_lpf(ResistorCapacitor *filter, float sample) {
float out = filter->prev_sample+(filter->alpha*(sample-filter->prev_sample));
filter->prev_sample = sample;
return out;
}

3
lib/filters.h
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@@ -17,3 +17,6 @@ void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate);
float apply_preemphasis(ResistorCapacitor *filter, float sample);
float hard_clip(float sample, float threshold);
void init_rc_lpf(ResistorCapacitor *filter, float cutoff, float sample_rate);
float apply_rc_lpf(ResistorCapacitor *filter, float sample);

6
src/fm95.c
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@@ -414,6 +414,10 @@ int main(int argc, char **argv) {
ResistorCapacitor preemp_l, preemp_r;
init_preemphasis(&preemp_l, preemphasis_tau, sample_rate);
init_preemphasis(&preemp_r, preemphasis_tau, sample_rate);
ResistorCapacitor lpf_l, lpf_r;
init_rc_lpf(&lpf_l, 15000, sample_rate);
init_rc_lpf(&lpf_r, 15000, sample_rate);
// #endregion
signal(SIGINT, stop);
@@ -471,6 +475,8 @@ int main(int argc, char **argv) {
float ready_l = apply_preemphasis(&preemp_l, l_in)*2;
float ready_r = apply_preemphasis(&preemp_r, r_in)*2;
ready_l = apply_rc_lpf(&lpf_l, ready_l);
ready_r = apply_rc_lpf(&lpf_r, ready_r);
ready_l = hard_clip(ready_l*audio_volume, clipper_threshold);
ready_r = hard_clip(ready_r*audio_volume, clipper_threshold);