Diff: WindowingDesignLpfHpf/WindowingDesignLH.cpp

Revision:

0:ea9a0c65a7dd

diff -r 000000000000 -r ea9a0c65a7dd WindowingDesignLpfHpf/WindowingDesignLH.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/WindowingDesignLpfHpf/WindowingDesignLH.cpp	Mon Nov 10 03:03:18 2014 +0000
@@ -0,0 +1,92 @@
+//------------------------------------------------------------------------------
+//  Design of FIR filter of LPF and HPF using window method
+//
+//  2014/11/09, Copyright (c) 2014 MIKAMI, Naoki
+//------------------------------------------------------------------------------
+
+#include "WindowingDesignLH.hpp"
+
+namespace Mikami
+{
+    WindowingDesign::WindowingDesign(int order, float fs)
+            : FS_(fs), PI_FS_(3.1415926536f/fs)
+    {
+        order_ = order;
+        if ((order % 2) != 0)
+        {
+            fprintf(stderr, "order must be even.");
+            return;
+        }
+        hm_ = new float[order/2+1];
+        wn_ = new float[order/2+1];    
+        
+        HammWindow();
+    }
+        
+    void WindowingDesign::Design(int order, Type pb, float fc,
+                                 float hk[])
+    {       
+        if (pb == LPF) fC_ = fc;
+        if (pb == HPF) fC_ = 0.5f*FS_ - fc;
+    
+        if (order != order_)
+        {
+            order_ = order_;
+            if (hm_ != NULL) delete[] hm_;
+            hm_ = new float[order/2+1];
+            if (wn_ != NULL) delete[] wn_;
+            wn_ = new float[order/2+1];
+            HammWindow();
+        }
+
+        // Calculate coefficients for LPF
+        LpfCoefficients();
+        // If HPF, transform coefficients
+        if (pb != LPF) ToHpf();
+        
+        for (int k=0; k<=order/2; k++)
+            hk[k] = hm_[order/2-k];
+
+        // For compensation of gain
+        float sum = hk[order_/2];
+        if (pb == LPF)
+            for (int k=0; k<order_/2; k++)
+                sum = sum + 2.0f*hk[k];
+        if (pb == HPF)
+        {
+            float sign = -1.0;
+            for (int k=order_/2-1; k>=0; k--)
+            {
+                sum = sum + sign*2.0f*hk[k];
+                sign = -sign;
+            }
+        }
+        for (int k=0; k<=order_/2; k++)
+            hk[k] = hk[k]/sum;
+    }
+
+    // Calculation of coefficients for LPF
+    void WindowingDesign::LpfCoefficients()
+    {
+        float w = 2.0f*PI_FS_*fC_;
+        hm_[0] = 2.0f*fC_/FS_;
+        for (int k=1; k<=order_/2; k++)
+            hm_[k] = (sinf(k*w)/(PI_*k))*wn_[k];  
+    }
+    
+    // Transform LPF to HPF
+    void WindowingDesign::ToHpf()
+    {
+        for (int k=1; k<=order_/2; k+=2)
+            hm_[k] = -hm_[k];
+    }    
+
+    // Hamming window
+    void WindowingDesign::HammWindow()
+    {
+        float pi2OvM = 2.0f*PI_/(float)(order_ + 1);
+        for (int n=0; n<=order_/2; n++)
+            wn_[n] = 0.54f + 0.46f*cosf(pi2OvM*n);
+    }
+}
+