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change lpf

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KubaPro010
2025-03-08 19:41:22 +01:00
parent b1c9e28844
commit 5de87c15a3
4 changed files with 42 additions and 83 deletions
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2
.vscode/.server-controller-port.log vendored
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@@ -1,5 +1,5 @@
{
"port": 13452,
"time": 1740903386827,
"time": 1741458712922,
"version": "0.0.3"
}

113
lib/filters.c
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@@ -11,92 +11,51 @@ float apply_preemphasis(ResistorCapacitor *filter, float sample) {
}
void init_lpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampleRate) {
// Calculate intermediate values
float omega = 2.0f * M_PI * cutoffFreq / sampleRate;
float sn = sinf(omega);
float cs = cosf(omega);
float alpha = sn / (2.0f * qFactor);
// Calculate coefficients
float b0 = (1.0f - cs) * 0.5f;
float b1 = 1.0f - cs;
float b2 = (1.0f - cs) * 0.5f;
float a0 = 1.0f + alpha;
float a1 = -2.0f * cs;
float a2 = 1.0f - alpha;
// Normalize by a0
filter->b0 = b0 / a0;
filter->b1 = b1 / a0;
filter->b2 = b2 / a0;
filter->a1 = a1 / a0;
filter->a2 = a2 / a0;
// Initialize state variables
filter->x1 = 0.0f;
filter->x2 = 0.0f;
filter->y1 = 0.0f;
filter->y2 = 0.0f;
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;
}
void init_hpf(BiquadFilter* filter, float cutoffFreq, float qFactor, float sampleRate) {
float omega = 2.0f * M_PI * cutoffFreq / sampleRate;
float alpha = sinf(omega) / (2.0f * qFactor);
float cosw = cosf(omega);
float b0 = (1.0f + cosw) / 2.0f;
float b1 = -(1.0f + cosw);
float b2 = (1.0f + cosw) / 2.0f;
float a0 = 1.0f + alpha;
float a1 = -2.0f * cosw;
float a2 = 1.0f - alpha;
// Normalize by a0
filter->b0 = b0 / a0;
filter->b1 = b1 / a0;
filter->b2 = b2 / a0;
filter->a1 = a1 / a0;
filter->a2 = a2 / a0;
// Initialize state variables
filter->x1 = 0.0f;
filter->x2 = 0.0f;
filter->y1 = 0.0f;
filter->y2 = 0.0f;
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 omega = 2.0f * M_PI * centerFreq / sampleRate;
float alpha = sinf(omega) / (2.0f * qFactor);
float cosw = cosf(omega);
float b0 = alpha;
float b1 = 0.0f;
float b2 = -alpha;
float a0 = 1.0f + alpha;
float a1 = -2.0f * cosw;
float a2 = 1.0f - alpha;
// Normalize by a0
filter->b0 = b0 / a0;
filter->b1 = b1 / a0;
filter->b2 = b2 / a0;
filter->a1 = a1 / a0;
filter->a2 = a2 / a0;
// Initialize state variables
filter->x1 = 0.0f;
filter->x2 = 0.0f;
filter->y1 = 0.0f;
filter->y2 = 0.0f;
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 out = input*filter->b0+filter->x1*filter->b1+filter->x2*filter->b2+filter->y1*filter->a1+filter->y2*filter->a2;
filter->y2 = filter->y1;
filter->y1 = out;
filter->x2 = filter->x1;
filter->x1 = 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;
}

8
lib/filters.h
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@@ -15,10 +15,10 @@ void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate);
float apply_preemphasis(ResistorCapacitor *filter, float sample);
typedef struct {
float b0, b1, b2;
float a1, a2;
float x1, x2;
float y1, y2;
// https://www.earlevel.com/main/2012/11/26/biquad-c-source-code/
float a0, a1, a2;
float b0, b1;
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);

2
src/fm95.c
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@@ -42,7 +42,7 @@
#define MPX_VOLUME 1.0f // Passtrough
#define MPX_CLIPPER_THRESHOLD 1.0f
#define LPF_CUTOFF 10000 // Should't need to be changed
#define LPF_CUTOFF 15000 // Should't need to be changed
volatile sig_atomic_t to_run = 1;