diff --git a/coeffs.hh b/coeffs.hh
new file mode 100644
index 0000000..d84118c
--- /dev/null
+++ b/coeffs.hh
@@ -0,0 +1,49 @@
+/*
+Coefficient array helper
+
+Copyright 2018 Ahmet Inan <inan@aicodix.de>
+*/
+
+#ifndef COEFFS_HH
+#define COEFFS_HH
+
+namespace DSP {
+
+template <typename TYPE>
+struct CoeffsFunc
+{
+	virtual TYPE operator () (int, int) = 0;
+	virtual ~CoeffsFunc() = default;
+};
+
+template <int TAPS, typename TYPE>
+class Coeffs
+{
+	TYPE w[TAPS];
+public:
+	Coeffs(CoeffsFunc<TYPE> *func)
+	{
+		for (int n = 0; n < TAPS; ++n)
+			w[n] = (*func)(n, TAPS);
+	}
+	Coeffs(CoeffsFunc<TYPE> *func0, CoeffsFunc<TYPE> *func1)
+	{
+		for (int n = 0; n < TAPS; ++n)
+			w[n] = (*func0)(n, TAPS) * (*func1)(n, TAPS);
+	}
+	void normalize(TYPE divisor = 1)
+	{
+		TYPE sum(0);
+		for (int n = 0; n < TAPS; ++n)
+			sum += w[n];
+		for (int n = 0; n < TAPS; ++n)
+			w[n] /= divisor * std::abs(sum);
+	}
+	inline TYPE operator () (int n) { return n >= 0 && n < TAPS ? w[n] : 0; }
+	inline operator const TYPE * () const { return w; }
+};
+
+}
+
+#endif
+
diff --git a/window.hh b/window.hh
index a3c7e5c..c01bf88 100644
--- a/window.hh
+++ b/window.hh
@@ -9,46 +9,18 @@ Copyright 2018 Ahmet Inan <inan@aicodix.de>
 
 #include "const.hh"
 #include "kahan.hh"
+#include "coeffs.hh"
 
 namespace DSP {
 
 template <typename TYPE>
-struct WinFunc
-{
-	virtual TYPE operator () (int, int) = 0;
-	virtual ~WinFunc() = default;
-};
-
-template <int TAPS, typename TYPE>
-class Window
-{
-	TYPE w[TAPS];
-public:
-	Window(WinFunc<TYPE> *func)
-	{
-		for (int n = 0; n < TAPS; ++n)
-			w[n] = (*func)(n, TAPS);
-	}
-	void normalize(TYPE divisor = 1)
-	{
-		TYPE sum(0);
-		for (int n = 0; n < TAPS; ++n)
-			sum += w[n];
-		for (int n = 0; n < TAPS; ++n)
-			w[n] /= divisor * std::abs(sum);
-	}
-	inline TYPE operator () (int n) { return n >= 0 && n < TAPS ? w[n] : 0; }
-	inline operator const TYPE * () const { return w; }
-};
-
-template <typename TYPE>
-struct Rect : public WinFunc<TYPE>
+struct Rect : public CoeffsFunc<TYPE>
 {
 	TYPE operator () (int n, int N) { return n >= 0 && n < N ? 1 : 0; }
 };
 
 template <typename TYPE>
-struct Hann : public WinFunc<TYPE>
+struct Hann : public CoeffsFunc<TYPE>
 {
 	TYPE operator () (int n, int N)
 	{
@@ -57,7 +29,7 @@ struct Hann : public WinFunc<TYPE>
 };
 
 template <typename TYPE>
-struct Hamming : public WinFunc<TYPE>
+struct Hamming : public CoeffsFunc<TYPE>
 {
 	TYPE operator () (int n, int N)
 	{
@@ -66,7 +38,7 @@ struct Hamming : public WinFunc<TYPE>
 };
 
 template <typename TYPE>
-class Lanczos : public WinFunc<TYPE>
+class Lanczos : public CoeffsFunc<TYPE>
 {
 	static TYPE sinc(TYPE x)
 	{
@@ -80,7 +52,7 @@ public:
 };
 
 template <typename TYPE>
-class Blackman : public WinFunc<TYPE>
+class Blackman : public CoeffsFunc<TYPE>
 {
 	TYPE a0, a1, a2;
 public:
@@ -95,7 +67,7 @@ public:
 };
 
 template <typename TYPE>
-class Gauss : public WinFunc<TYPE>
+class Gauss : public CoeffsFunc<TYPE>
 {
 	TYPE o;
 public:
@@ -107,7 +79,7 @@ public:
 };
 
 template <typename TYPE>
-class Kaiser : public WinFunc<TYPE>
+class Kaiser : public CoeffsFunc<TYPE>
 {
 	TYPE a;
 	/*