Futher WIP

src/libfir++/200_CommonFilters.cc

@@ -15,6 +15,14 @@ SincLowpass(int npoints, double corner, double gain)
 
 
 
+Filter
+BlackmanLowpass(int npoints, double corner, double gain)
+{
+    return Filter(fir_blackman_lowpass(npoints, corner, gain));
+}
+
+
+
 Filter
 LanczosLowpass(int npoints, double corner, double gain, int a)
 {

src/libfir++/200_CommonFilters.h

@@ -38,6 +38,8 @@ Filter SincLowpass(int npoints, double corner, double gain);
 
 
 
+Filter BlackmanLowpass(int npoints, double corner, double gain);
+
 Filter LanczosLowpass(int npoints, double corner, double gain, int a);
 
 

src/libfir/200_common_filters.c

@@ -7,8 +7,27 @@
 
 
 
-struct fir_filter_t*
-fir_sinc_lowpass(int npoints, double corner, double gain)
+static double
+window_rectangle(int n, int N)
+{
+    return 1.0;
+}
+
+
+
+static double
+window_blackman(int n, int N)
+{
+    double v = 2 * M_PI * n;
+    v /= N;
+    return 0.42 - 0.5 * cos(v) + 0.08 * cos(2 * v);
+}
+
+
+
+static struct fir_filter_t*
+fir_windowed_lowpass(int npoints, double corner, double gain,
+    double (*window)(int n, int N))
 {
     double* coeff, t, sum = 0;
     int i, spoints;
@@ -25,12 +44,12 @@ fir_sinc_lowpass(int npoints, double corner, double gain)
     /* only fill out for t ≤ 0 */
     for(i = 0; i < spoints; ++i) {
         if((i * 2 + 1) == npoints) {
-            coeff[i] = 1;
-            sum += 1; /* not 2, as we don't repeat this coeff */
+            coeff[i] = window(i, npoints) * 1;
+            sum += coeff[i]; /* not 2, as we don't repeat this coeff */
         } else {
             t = i + 0.5 - npoints * 0.5;
             t *= corner * 2 * M_PI;
-            coeff[i] = sin(t) / t;
+            coeff[i] = window(i, npoints) * sin(t) / t;
             sum += coeff[i] * 2;
         }
     }
@@ -47,6 +66,22 @@ fir_sinc_lowpass(int npoints, double corner, double gain)
 
 
 
+struct fir_filter_t*
+fir_sinc_lowpass(int npoints, double corner, double gain)
+{
+    return fir_windowed_lowpass(npoints, corner, gain, window_rectangle);
+}
+
+
+
+struct fir_filter_t*
+fir_blackman_lowpass(int npoints, double corner, double gain)
+{
+    return fir_windowed_lowpass(npoints, corner, gain, window_blackman);
+}
+
+
+
 struct fir_filter_t*
 fir_lanczos_lowpass(int npoints, double corner, double gain, int a)
 {

src/libfir/200_common_filters.h

@@ -45,6 +45,10 @@ struct fir_filter_t* fir_lanczos_lowpass(int npoints, double corner, double gain
 
 
 
+struct fir_filter_t* fir_blackman_lowpass(int npoints, double corner, double gain);
+
+
+
 /*!@}*/
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