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make lpf a IIR

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This commit is contained in:
KubaPro010
2025-01-02 01:01:14 +01:00
parent d9625757b3
commit 9ddee9239d
7 changed files with 17 additions and 35 deletions
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29
lib/filters.c
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@@ -12,32 +12,15 @@ float apply_pre_emphasis(Emphasis *pe, float sample) {
}
void init_low_pass_filter(LowPassFilter *lp, float cutoff_frequency, 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 * cutoff_frequency * 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;
}
}
memset(lp->sample_buffer, 0, sizeof(lp->sample_buffer));
lp->buffer_index = 0;
float rc = 1/(M_2PI*cutoff_frequency);
lp->alpha = sample_rate/(sample_rate+rc);
lp->prev_sample = 0.0f;
}
float apply_low_pass_filter(LowPassFilter *lp, float sample) {
// Update the sample buffer
lp->sample_buffer[lp->buffer_index] = sample;
lp->buffer_index = (lp->buffer_index + 1) % FIR_TAPS;
// Apply the filter
float result = 0.0f;
int index = lp->buffer_index;
for (int i = 0; i < FIR_TAPS; i++) {
result += lp->low_pass_fir[0][i] * lp->sample_buffer[index];
index = (index + 1) % FIR_TAPS;
}
return result*6;
float output = lp->alpha*sample+(1-lp->alpha)*lp->prev_sample;
lp->prev_sample = output;
return output;
}
void init_delay_line(DelayLine *delay_line, int max_delay) {

5
lib/filters.h
View File

@@ -15,9 +15,8 @@ void init_emphasis(Emphasis *pe, float tau, float sample_rate);
float apply_pre_emphasis(Emphasis *pe, float sample);
typedef struct {
float low_pass_fir[FIR_PHASES][FIR_TAPS];
float sample_buffer[FIR_TAPS];
int buffer_index;
float alpha;
float prev_sample;
} LowPassFilter;
void init_low_pass_filter(LowPassFilter *lp, float cutoff_frequency, float sample_rate);