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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 This file 2005-2006 Christian Landone.
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7
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8 This program is free software; you can redistribute it and/or
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9 modify it under the terms of the GNU General Public License as
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10 published by the Free Software Foundation; either version 2 of the
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11 License, or (at your option) any later version. See the file
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12 COPYING included with this distribution for more information.
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13 */
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14
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15 #ifndef QM_DSP_DECIMATOR_H
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16 #define QM_DSP_DECIMATOR_H
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17
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18 /**
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19 * Decimator carries out a fast downsample by a power-of-two
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20 * factor. Only a limited number of factors are supported, from two to
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21 * whatever getHighestSupportedFactor() returns. This is much faster
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22 * than Resampler but has a worse signal-noise ratio.
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23 */
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24 class Decimator
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25 {
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26 public:
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27 /**
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28 * Construct a Decimator to operate on input blocks of length
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29 * inLength, with decimation factor decFactor. inLength should be
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30 * a multiple of decFactor. Output blocks will be of length
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31 * inLength / decFactor.
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32 *
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33 * decFactor must be a power of two. The highest supported factor
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34 * is obtained through getHighestSupportedFactor(); for higher
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35 * factors, you will need to chain more than one decimator.
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36 */
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37 Decimator(int inLength, int decFactor);
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38 virtual ~Decimator();
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39
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40 /**
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41 * Process inLength samples (as supplied to constructor) from src
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42 * and write inLength / decFactor samples to dst. Note that src
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43 * and dst may be the same or overlap (an intermediate buffer is
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44 * used).
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45 */
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46 void process( const double* src, double* dst );
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47
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48 /**
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49 * Process inLength samples (as supplied to constructor) from src
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50 * and write inLength / decFactor samples to dst. Note that src
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51 * and dst may be the same or overlap (an intermediate buffer is
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52 * used).
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53 */
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54 void process( const float* src, float* dst );
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55
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56 int getFactor() const { return m_decFactor; }
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57 static int getHighestSupportedFactor() { return 8; }
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58
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59 void resetFilter();
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60
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61 private:
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62 void deInitialise();
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63 void initialise( int inLength, int decFactor );
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64 void doAntiAlias( const double* src, double* dst, int length );
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65 void doAntiAlias( const float* src, double* dst, int length );
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66
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67 int m_inputLength;
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68 int m_outputLength;
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69 int m_decFactor;
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70
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71 double Input;
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72 double Output ;
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73
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74 double o1,o2,o3,o4,o5,o6,o7;
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75
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76 double a[ 9 ];
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77 double b[ 9 ];
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78
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79 double* decBuffer;
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80 };
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81
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82 #endif //
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