add functional lpf, remake hilbert

2026-07-30 08:19:14 +02:00 · 2025-01-26 19:26:20 +01:00
parent d2663bdb9f
commit 16fa3f3702
7 changed files with 144 additions and 66 deletions
@@ -16,6 +16,82 @@ float apply_pre_emphasis(ResistorCapacitor *rc, float sample) {
    return audio;
 }

+void init_lpf(FrequencyFilter* filter, float cutoffFreq, float sampleRate) {
+    float nyquist = sampleRate / 2.0f;
+    float fc = cutoffFreq / nyquist;
+    
+    // Blackman window for sharp transition
+    for (int n = 0; n < FILTER_TAPS; n++) {
+        float m = n - (FILTER_TAPS - 1.0f) / 2.0f;
+        
+        // Sinc function
+        float sinc = (m == 0) ? 1.0f : sinf(PI * m * fc) / (PI * m);
+        
+        // Blackman window
+        float window = 0.42f - 0.5f * cosf(2.0f * PI * n / (FILTER_TAPS - 1)) 
+                     + 0.08f * cosf(4.0f * PI * n / (FILTER_TAPS - 1));
+        
+        filter->coeffs[n] = sinc * window;
+    }
+    
+    // Normalize
+    float sum = 0;
+    for (int i = 0; i < FILTER_TAPS; i++) sum += filter->coeffs[i];
+    for (int i = 0; i < FILTER_TAPS; i++) filter->coeffs[i] /= sum;
+    
+    // Clear delay line
+    memset(filter->delay, 0, sizeof(filter->delay));
+    filter->index = 0;
+}
+
+void init_hpf(FrequencyFilter* filter, float cutoffFreq, float sampleRate) {
+    float nyquist = sampleRate / 2.0f;
+    float fc = cutoffFreq / nyquist;
+    
+    // Blackman window for sharp transition
+    for (int n = 0; n < FILTER_TAPS; n++) {
+        float m = n - (FILTER_TAPS - 1.0f) / 2.0f;
+        
+        // Sinc function
+        float sinc = (m == 0) ? -1.0f : sinf(PI * m * fc) / (PI * m);
+        
+        // Blackman window
+        float window = 0.42f - 0.5f * cosf(2.0f * PI * n / (FILTER_TAPS - 1)) 
+                     + 0.08f * cosf(4.0f * PI * n / (FILTER_TAPS - 1));
+        
+        filter->coeffs[n] = sinc * window;
+    }
+
+    filter->coeffs[FILTER_TAPS/2] += 1.0f;
+    
+    // Normalize
+    float sum = 0;
+    for (int i = 0; i < FILTER_TAPS; i++) sum += filter->coeffs[i];
+    for (int i = 0; i < FILTER_TAPS; i++) filter->coeffs[i] /= sum;
+    
+    // Clear delay line
+    memset(filter->delay, 0, sizeof(filter->delay));
+    filter->index = 0;
+}
+
+float apply_freqeuncy_filter(FrequencyFilter* filter, float input) {
+    // Shift delay line
+    filter->delay[filter->index] = input;
+    
+    // Compute output
+    float output = 0;
+    int j = filter->index;
+    for (int i = 0; i < FILTER_TAPS; i++) {
+        output += filter->coeffs[i] * filter->delay[j];
+        j = (j + 1) % FILTER_TAPS;
+    }
+    
+    // Update index
+    filter->index = (filter->index + FILTER_TAPS - 1) % FILTER_TAPS;
+    
+    return output;
+}
+
 void init_delay_line(DelayLine *delay_line, int max_delay) {
    delay_line->buffer = (float *)calloc(max_delay, sizeof(float));
    delay_line->size = max_delay;