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5
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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * awgn.h - An additive Gaussian white noise generator
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5 *
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6 * Written by Steve Underwood <steveu@coppice.org>
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7 *
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8 * Copyright (C) 2001 Steve Underwood
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9 *
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10 * All rights reserved.
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11 *
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12 * This program is free software; you can redistribute it and/or modify
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13 * it under the terms of the GNU General Public License version 2, as
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14 * published by the Free Software Foundation.
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15 *
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16 * This program is distributed in the hope that it will be useful,
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17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 * GNU General Public License for more details.
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20 *
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21 * You should have received a copy of the GNU General Public License
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22 * along with this program; if not, write to the Free Software
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23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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24 *
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25 * $Id: awgn.h,v 1.8 2006/10/24 13:45:27 steveu Exp $
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26 */
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27
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28 /*! \file */
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29
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30 /* This code is based on some demonstration code in a research
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31 paper somewhere. I can't track down where I got the original from,
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32 so that due recognition can be given. The original had no explicit
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33 copyright notice, and I hope nobody objects to its use here.
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34
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35 Having a reasonable Gaussian noise generator is pretty important for
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36 telephony testing (in fact, pretty much any DSP testing), and this
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37 one seems to have served me OK. Since the generation of Gaussian
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38 noise is only for test purposes, and not a core system component,
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39 I don't intend to worry excessively about copyright issues, unless
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40 someone worries me.
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41
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42 The non-core nature of this code also explains why it is unlikely
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43 to ever be optimised. */
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44
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45 #if !defined(_AWGN_H_)
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46 #define _AWGN_H_
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47
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48 /*! \page awgn_page Additive white gaussian noise (AWGN) generation
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49
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50 \section awgn_page_sec_1 What does it do?
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51 Adding noise is not the most useful thing in most DSP applications, but it is
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52 awfully useful for test suites.
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53
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54 \section awgn_page_sec_2 How does it work?
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55
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56 This code is based on some demonstration code in a research paper somewhere. I
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57 can't track down where I got the original from, so that due recognition can be
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58 given. The original had no explicit copyright notice, and I hope nobody objects
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59 to its use here.
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60
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61 Having a reasonable Gaussian noise generator is pretty important for telephony
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62 testing (in fact, pretty much any DSP testing), and this one seems to have
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63 served me OK. Since the generation of Gaussian noise is only for test purposes,
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64 and not a core system component, I don't intend to worry excessively about
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65 copyright issues, unless someone worries me.
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66
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67 The non-core nature of this code also explains why it is unlikely to ever be
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68 optimised.
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69 */
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70
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71 /*!
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72 AWGN generator descriptor. This contains all the state information for an AWGN generator.
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73 */
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74 typedef struct
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75 {
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76 double rms;
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77 long int ix1;
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78 long int ix2;
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79 long int ix3;
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80 double r[98];
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81 double gset;
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82 int iset;
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83 } awgn_state_t;
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84
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85 #ifdef __cplusplus
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86 extern "C" {
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87 #endif
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88
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89 void awgn_init_dbm0(awgn_state_t *s, int idum, float level);
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90
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91 void awgn_init_dbov(awgn_state_t *s, int idum, float level);
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92
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93 int16_t awgn(awgn_state_t *s);
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94
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95 #ifdef __cplusplus
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96 }
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97 #endif
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98
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99 #endif
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100 /*- End of file ------------------------------------------------------------*/
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