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1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
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2 /*
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3 QM DSP Library
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4
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5 Centre for Digital Music, Queen Mary, University of London.
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6
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7 This program is free software; you can redistribute it and/or
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8 modify it under the terms of the GNU General Public License as
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9 published by the Free Software Foundation; either version 2 of the
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10 License, or (at your option) any later version. See the file
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11 COPYING included with this distribution for more information.
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12 */
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13
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14 #ifndef DECIMATORB_H
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15 #define DECIMATORB_H
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16
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17 #include <vector>
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18
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19 /**
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20 * DecimatorB carries out a fast downsample by a power-of-two
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21 * factor. It only knows how to decimate by a factor of 2, and will
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22 * use repeated decimation for higher factors. A Butterworth filter of
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23 * order 6 is used for the lowpass filter.
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24 */
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25 class DecimatorB
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26 {
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27 public:
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28 void process( const double* src, double* dst );
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29 void process( const float* src, float* dst );
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30
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31 /**
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32 * Construct a DecimatorB to operate on input blocks of length
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33 * inLength, with decimation factor decFactor. inLength should be
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34 * a multiple of decFactor. Output blocks will be of length
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35 * inLength / decFactor.
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36 *
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37 * decFactor must be a power of two.
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38 */
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39 DecimatorB(int inLength, int decFactor);
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40 virtual ~DecimatorB();
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41
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42 int getFactor() const { return m_decFactor; }
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43
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44 private:
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45 void deInitialise();
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46 void initialise(int inLength, int decFactor);
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47 void doAntiAlias(const double* src, double* dst, int length, int filteridx);
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48 void doProcess();
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49
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50 int m_inputLength;
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51 int m_outputLength;
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52 int m_decFactor;
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53
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54 std::vector<std::vector<double> > m_o;
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55
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56 double m_a[7];
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57 double m_b[7];
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58
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59 double *m_aaBuffer;
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60 double *m_tmpBuffer;
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61 };
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62
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63 #endif
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64
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