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diff --git a/libaf/filter.h b/libaf/filter.h
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+/*=============================================================================
+//	
+//  This software has been released under the terms of the GNU Public
+//  license. See http://www.gnu.org/copyleft/gpl.html for details.
+//
+//  Copyright 2001 Anders Johansson ajh@atri.curtin.edu.au
+//
+//=============================================================================
+*/
+
+#if !defined _DSP_H
+# error "Never use <filter.h> directly; include <dsp.h> instead"
+#endif
+
+#ifndef _FILTER_H
+#define _FILTER_H	1
+
+
+// Design and implementation of different types of digital filters 
+
+
+// Flags used for filter design
+
+// Filter characteristics
+#define LP          0x00010000 // Low pass
+#define HP          0x00020000 // High pass
+#define BP          0x00040000 // Band pass
+#define BS          0x00080000 // Band stop
+#define TYPE_MASK   0x000F0000
+
+// Window types
+#define BOXCAR      0x00000001
+#define TRIANG      0x00000002
+#define HAMMING     0x00000004
+#define HANNING     0x00000008
+#define BLACKMAN    0x00000010
+#define FLATTOP     0x00000011
+#define KAISER      0x00000012
+#define WINDOW_MASK 0x0000001F
+
+// Parallel filter design
+#define	FWD   	    0x00000001 // Forward indexing of polyphase filter
+#define REW         0x00000002 // Reverse indexing of polyphase filter
+#define ODD         0x00000010 // Make filter HP
+
+// Exported functions
+extern _ftype_t fir(unsigned int n, _ftype_t* w, _ftype_t* x);
+extern _ftype_t* pfir(unsigned int n, unsigned int k, unsigned int xi, _ftype_t** w, _ftype_t** x, _ftype_t* y, unsigned int s);
+
+extern int updateq(unsigned int n, unsigned int xi, _ftype_t* xq, _ftype_t* in);
+extern int updatepq(unsigned int n, unsigned int k, unsigned int xi, _ftype_t** xq, _ftype_t* in, unsigned int s);
+
+extern int design_fir(unsigned int n, _ftype_t* w, _ftype_t* fc, unsigned int flags, _ftype_t opt);
+extern int design_pfir(unsigned int n, unsigned int k, _ftype_t* w, _ftype_t** pw, _ftype_t g, unsigned int flags);
+
+/* Add new data to circular queue designed to be used with a FIR
+   filter. xq is the circular queue, in pointing at the new sample, xi
+   current index for xq and n the length of the filter. xq must be n*2
+   long. 
+*/
+#define updateq(n,xi,xq,in)\
+  xq[xi]=xq[xi+n]=*in;\
+  xi=(++xi)&(n-1);
+
+#endif