radio95/fm95
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refactor filter functions and update FM modulator logic

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KubaPro010
2025-03-08 19:53:59 +01:00
parent 6acb8cd5da
commit 90fabff616
5 changed files with 12 additions and 40 deletions
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30
lib/filters.c
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@@ -24,35 +24,7 @@ void init_lpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampl
filter->z2 = 0.0f;
}
void init_hpf(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 = 1.0f*norm;
filter->a1 = -2.0f*norm;
filter->a2 = 1.0f*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;
}
void init_bpf(BiquadFilter* filter, float centerFreq, float qFactor, float sampleRate) {
float cutoffNorm = centerFreq / sampleRate;
float K = tanf(M_PI * cutoffNorm);
float norm = 1.0f/(1.0f+K/qFactor+K*K);
filter->a0 = K/qFactor*norm;
filter->a1 = 0.0f;
filter->a2 = -K/qFactor*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_frequency_filter(BiquadFilter* filter, float input) {
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;

4
lib/filters.h
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@@ -21,9 +21,7 @@ typedef struct {
float z1, z2;
} BiquadFilter;
void init_lpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampleRate);
void init_hpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampleRate);
void init_bpf(BiquadFilter* filter, float centerFreq, float qFactor, float sampleRate);
float apply_frequency_filter(BiquadFilter* filter, float input);
float apply_biquad(BiquadFilter* filter, float input);
float hard_clip(float sample, float threshold);
float voltage_db_to_voltage(float db);

7
lib/fm_modulator.c
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@@ -3,12 +3,13 @@
void init_fm_modulator(FMModulator *fm, float frequency, float deviation, float sample_rate) {
fm->frequency = frequency;
fm->deviation = deviation;
init_oscillator(&fm->osc, frequency, sample_rate);
fm->sample_rate = sample_rate;
fm->osc_phase = 0.0f;
}
float modulate_fm(FMModulator *fm, float sample) {
float inst_freq = fm->frequency+(sample*fm->deviation);
if (inst_freq < 0.0f) inst_freq = 0.0f;
change_oscillator_frequency(&fm->osc, inst_freq);
return get_oscillator_sin_sample(&fm->osc);
fm->osc_phase += fmodf(fm->osc_phase + ((M_2PI * inst_freq) / fm->sample_rate), M_2PI);
return sinf(fm->osc_phase);
}

3
lib/fm_modulator.h
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@@ -6,7 +6,8 @@ typedef struct
{
float frequency;
float deviation;
Oscillator osc;
float osc_phase;
float sample_rate;
} FMModulator;
void init_fm_modulator(FMModulator *fm, float frequency, float deviation, float sample_rate);

8
src/fm95.c
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@@ -414,10 +414,10 @@ int main(int argc, char **argv) {
float current_mpx_in = mpx_in[i];
float current_sca_in = sca_in[i];
float ready_l = apply_frequency_filter(&lpf_l, l_in);
float ready_r = apply_frequency_filter(&lpf_r, r_in);
ready_l = apply_preemphasis(&preemp_l, ready_l)*4;
ready_r = apply_preemphasis(&preemp_r, ready_r)*4;
float ready_l = apply_biquad(&lpf_l, l_in);
float ready_r = apply_biquad(&lpf_r, r_in);
ready_l = apply_preemphasis(&preemp_l, ready_l)*2;
ready_r = apply_preemphasis(&preemp_r, ready_r)*2;
ready_l = hard_clip(ready_l*audio_volume, clipper_threshold);
ready_r = hard_clip(ready_r*audio_volume, clipper_threshold);