diff --git a/doc24652.pdf b/doc24652.pdf
new file mode 100644
index 0000000..4d04bce
Binary files /dev/null and b/doc24652.pdf differ
diff --git a/filter.c b/filter.c
index 0e1ee24..7cd9b29 100644
--- a/filter.c
+++ b/filter.c
@@ -213,14 +213,49 @@ ChebFilter* create_che_filter(int NP, double PR, int LH, double FC) {
   return(filter);
 }
 
-ChebFilter* create_bw_low_pass_filter(int NP, double FC) {
-  return(create_che_filter(NP, 0, 0, FC));
+dChebFilter* create_bw_low_pass_filter(int NP, double FC) {
+  dChebFilter *filter=(dChebFilter*)malloc(sizeof(dChebFilter));
+
+  filter->type=0;
+  filter->lp_filter=create_che_filter(NP, 0, 0, FC);
+  filter->hp_filter=NULL;
+
+  return(filter);
 }
 
-ChebFilter* create_bw_high_pass_filter(int NP, double FC) {
-  return(create_che_filter(NP, 0, 1, FC));
+dChebFilter* create_bw_high_pass_filter(int NP, double FC) {
+  dChebFilter *filter=(dChebFilter*)malloc(sizeof(dChebFilter));
+
+  filter->type=1;
+  filter->lp_filter=NULL;
+  filter->hp_filter=create_che_filter(NP, 0, 1, FC);
+
+  return(filter);
 }
 
+dChebFilter* create_bw_bp_pass_filter(int NP, double FC, double winwidth) {
+  dChebFilter *filter=(dChebFilter*)malloc(sizeof(dChebFilter));
+
+  filter->type=2;
+  filter->lp_filter=create_che_filter(NP, 0, 0, FC*(1.0+fabsl(winwidth)));
+  filter->hp_filter=create_che_filter(NP, 0, 1, FC*(1.0-fabsl(winwidth)));
+
+  return(filter);
+}
+
+double applydfilter(dChebFilter* filter, double X0) {
+  double output=X0;
+
+  if(filter->lp_filter!=NULL)
+    output=applyfilter(filter->lp_filter, output);
+
+  if(filter->hp_filter!=NULL)
+    output=applyfilter(filter->hp_filter, output);
+
+  return(output);
+}
+
+
 ChebFilter* create_che_low_pass_filter(int NP, double FC, double PR) {
   return(create_che_filter(NP, PR, 0, FC));
 }
diff --git a/filter.h b/filter.h
index a891f68..83cef5d 100644
--- a/filter.h
+++ b/filter.h
@@ -1,14 +1,14 @@
 
 typedef struct filter {
-  double a[20];
-  double b[20];
+  double a[20]; // inputs coefficients
+  double b[20]; // output coefficients
 
-  double X[20];
-  double Y[20];
+  double X[20]; // history of inputs
+  double Y[20]; // history of outputs
 
-  int    NP;
+  int    NP;    // Nomber of Poles - Order
 
-  double a0;
+  double a0;    // internal
   double a1;
   double a2;
   double b0;
@@ -16,13 +16,22 @@ typedef struct filter {
   double b2;
 } ChebFilter;
 
+
+typedef struct doublefilter {
+  int         type;
+  ChebFilter  *lp_filter;
+  ChebFilter  *hp_filter;
+} dChebFilter;
+
 ChebFilter* call_205(int P, ChebFilter* filter, double FC, int NP, int LH, double PR);
 
 ChebFilter* create_che_filter(int NP, double PR, int LH, double FC);
-ChebFilter* create_bw_low_pass_filter(int NP, double FC);
-
-ChebFilter* create_bw_high_pass_filter(int NP, double FC);
 ChebFilter* create_che_low_pass_filter(int NP, double FC, double PR);
 ChebFilter* create_che_high_pass_filter(int NP, double FC, double PR);
 
+
+dChebFilter* create_bw_low_pass_filter(int NP, double FC);
+dChebFilter* create_bw_high_pass_filter(int NP, double FC);
+dChebFilter* create_bw_bp_pass_filter(int NP, double FC, double winwidth);
+
 double applyfilter(ChebFilter* filter, double X0);
\ No newline at end of file