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33 lines
1.0 KiB
C
33 lines
1.0 KiB
C
#include "iir.h"
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void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate, float ref_freq) {
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float dt = 1.0f / sample_rate;
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filter->alpha = tau / (tau + dt);
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float omega = M_2PI * ref_freq / sample_rate;
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filter->gain = 1.0f / sqrtf(1.0f + filter->alpha * filter->alpha - 2.0f * filter->alpha * cosf(omega));
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filter->prev_sample = 0.0f;
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}
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inline float apply_preemphasis(ResistorCapacitor *filter, float sample) {
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float out = (sample - filter->alpha * filter->prev_sample) * filter->gain;
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filter->prev_sample = sample;
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return out;
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}
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void tilt_init(TiltCorrectionFilter* filter, float alpha) {
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filter->alpha = alpha; // 0.95 to 0.99 typically
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filter->x_prev = 0.0f;
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filter->y_prev = 0.0f;
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}
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float tilt(TiltCorrectionFilter* filter, float input) {
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// High-pass: y[n] = α*y[n-1] + (x[n] - x[n-1])
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float output = filter->alpha * filter->y_prev + (input - filter->x_prev);
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filter->x_prev = input;
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filter->y_prev = output;
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return output;
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}
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