diff dsp/rateconversion/DecimatorB.h @ 380:1494e18439ae

Add DecimatorB (Butterworth filter, arbitrary powers of two)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dsp/rateconversion/DecimatorB.h	Tue Oct 22 08:58:28 2013 +0100
@@ -0,0 +1,64 @@
+/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
+/*
+    QM DSP Library
+
+    Centre for Digital Music, Queen Mary, University of London.
+
+    This program is free software; you can redistribute it and/or
+    modify it under the terms of the GNU General Public License as
+    published by the Free Software Foundation; either version 2 of the
+    License, or (at your option) any later version.  See the file
+    COPYING included with this distribution for more information.
+*/
+
+#ifndef DECIMATORB_H
+#define DECIMATORB_H
+
+#include <vector>
+
+/**
+ * DecimatorB carries out a fast downsample by a power-of-two
+ * factor. It only knows how to decimate by a factor of 2, and will
+ * use repeated decimation for higher factors. A Butterworth filter of
+ * order 6 is used for the lowpass filter.
+ */
+class DecimatorB
+{
+public:
+    void process( const double* src, double* dst );
+    void process( const float* src, float* dst );
+
+    /**
+     * Construct a DecimatorB to operate on input blocks of length
+     * inLength, with decimation factor decFactor.  inLength should be
+     * a multiple of decFactor.  Output blocks will be of length
+     * inLength / decFactor.
+     *
+     * decFactor must be a power of two.
+     */
+    DecimatorB(int inLength, int decFactor);
+    virtual ~DecimatorB();
+
+    int getFactor() const { return m_decFactor; }
+
+private:
+    void deInitialise();
+    void initialise(int inLength, int decFactor);
+    void doAntiAlias(const double* src, double* dst, int length, int filteridx);
+    void doProcess();
+
+    int m_inputLength;
+    int m_outputLength;
+    int m_decFactor;
+
+    std::vector<std::vector<double> > m_o;
+
+    double m_a[7];
+    double m_b[7];
+	
+    double *m_aaBuffer;
+    double *m_tmpBuffer;
+};
+
+#endif
+