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Code Issues Activity

get rid of lpf as it barely works, swh-plugin's lowpass_iir_1891 works better

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KubaPro010
2025-03-09 09:35:10 +01:00
parent 2c18edc6a8
commit 0a99e3364c
4 changed files with 3 additions and 46 deletions
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2
.vscode/.server-controller-port.log vendored
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@@ -1,5 +1,5 @@
{
"port": 13452,
"time": 1741463839184,
"time": 1741509228803,
"version": "0.0.3"
}

21
lib/filters.c
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@@ -10,27 +10,6 @@ float apply_preemphasis(ResistorCapacitor *filter, float sample) {
return out;
}
void init_lpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampleRate) {
float cutoffNorm = cutoffFreq / sampleRate;
float K = tanf(M_PI * cutoffNorm);
float norm = 1.0f/(1.0f+K/qFactor+K*K);
filter->a0 = K*K*norm;
filter->a1 = 2.0f*K*K*norm;
filter->a2 = K*K*norm;
filter->b1 = 2.0f*(K*K-1.0f)*norm;
filter->b2 = (1.0f-K/qFactor+K*K)*norm;
filter->z1 = 0.0f;
filter->z2 = 0.0f;
}
float apply_biquad(BiquadFilter* filter, float input) {
float out = input*filter->a0+filter->z1;
filter->z1 = input*filter->a1+filter->z2-filter->b1*out;
filter->z2 = input*filter->a2-filter->b2*out;
return out;
}
float hard_clip(float sample, float threshold) {
if (sample > threshold) {

9
lib/filters.h
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@@ -14,15 +14,6 @@ typedef struct
void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate);
float apply_preemphasis(ResistorCapacitor *filter, float sample);
typedef struct {
// https://www.earlevel.com/main/2012/11/26/biquad-c-source-code/
float a0, a1, a2;
float b1, b2;
float z1, z2;
} BiquadFilter;
void init_lpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampleRate);
float apply_biquad(BiquadFilter* filter, float input);
float hard_clip(float sample, float threshold);
float voltage_db_to_voltage(float db);
float power_db_to_voltage(float db);

17
src/fm95.c
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@@ -40,8 +40,6 @@
#define MPX_VOLUME 1.0f // Passtrough
#define MPX_CLIPPER_THRESHOLD 1.0f
#define LPF_CUTOFF 15000 // Should't need to be changed
volatile sig_atomic_t to_run = 1;
void uninterleave(const float *input, float *left, float *right, size_t num_samples) {
@@ -368,13 +366,6 @@ 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);
// Use https://www.earlevel.com/main/2021/09/02/biquad-calculator-v3/
BiquadFilter lpf_l1, lpf_r1, lpf_l2, lpf_r2;
init_lpf(&lpf_l1, LPF_CUTOFF, 0.70710678f, SAMPLE_RATE);
init_lpf(&lpf_r1, LPF_CUTOFF, 0.70710678f, SAMPLE_RATE);
init_lpf(&lpf_l2, LPF_CUTOFF, 0.70710678f/2.0f, SAMPLE_RATE);
init_lpf(&lpf_r2, LPF_CUTOFF, 0.70710678f/2.0f, SAMPLE_RATE);
// #endregion
signal(SIGINT, stop);
@@ -415,12 +406,8 @@ int main(int argc, char **argv) {
float current_mpx_in = mpx_in[i];
float current_sca_in = sca_in[i];
float ready_l = apply_biquad(&lpf_l1, l_in);
float ready_r = apply_biquad(&lpf_r1, r_in);
ready_l = apply_biquad(&lpf_l2, ready_l);
ready_r = apply_biquad(&lpf_r2, ready_r);
ready_l = apply_preemphasis(&preemp_l, ready_l)*2;
ready_r = apply_preemphasis(&preemp_r, ready_r)*2;
float ready_l = apply_preemphasis(&preemp_l, l_in)*2;
float ready_r = apply_preemphasis(&preemp_r, r_in)*2;
ready_l = hard_clip(ready_l*audio_volume, clipper_threshold);
ready_r = hard_clip(ready_r*audio_volume, clipper_threshold);