radio95/fm95
0
1
Fork 0
mirror of https://github.com/radio95-rnt/fm95.git synced 2026-02-26 11:22:00 +01:00
Code Issues Activity

remove lpf and add normalization to the preemp

Browse Source
This commit is contained in:
KubaPro010
2025-03-26 19:26:40 +01:00
parent 6a83a18cf4
commit 2e36f34b4a
5 changed files with 9 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
.vscode/.server-controller-port.log vendored
View File

@@ -1,5 +1,5 @@
{
"port": 13452,
"time": 1742991617814,
"time": 1743013405321,
"version": "0.0.3"
}

2
README.md
View File

@@ -33,7 +33,7 @@ Done!
## CPU Usage?
Should run completly fine on a pi 5, right now with the preemp, on a pi 3b, its 32%
Should run completly fine on a pi 5, right now with the preemp and rds2, on a pi 3b, its 25%
## Recommendations

17
lib/filters.c
View File

@@ -2,26 +2,15 @@
void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate) {
filter->prev_sample = 0.0f;
filter->alpha = exp(-1 / (tau*sample_rate));
filter->alpha = expf(-1 / (tau*sample_rate));
filter->gain = 1.0f / (1.0f - filter->alpha);
}
float apply_preemphasis(ResistorCapacitor *filter, float sample) {
float out = sample-filter->alpha*filter->prev_sample;
float out = (sample - filter->alpha * filter->prev_sample) * filter->gain;
filter->prev_sample = sample;
return out;
}
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;
}

8
lib/filters.h
View File

@@ -5,18 +5,14 @@
#include "constants.h"
#include "oscillator.h"
#define FILTER_LEN 51
typedef struct
{
float alpha;
float prev_sample;
float gain;
} ResistorCapacitor;
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);
float hard_clip(float sample, float threshold);

10
src/fm95.c
View File

@@ -414,10 +414,6 @@ 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);
@@ -473,10 +469,8 @@ int main(int argc, char **argv) {
float current_rds2_in = rds2_in[i];
float current_sca_in = sca_in[i];
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);
float ready_l = apply_preemphasis(&preemp_l, l_in);
float ready_r = apply_preemphasis(&preemp_r, r_in);
ready_l = hard_clip(ready_l*audio_volume, clipper_threshold);
ready_r = hard_clip(ready_r*audio_volume, clipper_threshold);