Mercurial > hg > audiostuff
annotate spandsp-0.0.6pre17/src/spandsp/noise.h @ 6:22a74b01a099 default tip
implement more meaningful test program
author | Peter Meerwald <pmeerw@cosy.sbg.ac.at> |
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date | Fri, 25 Jun 2010 16:14:50 +0200 |
parents | 26cd8f1ef0b1 |
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rev | line source |
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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 * noise.h - A low complexity audio noise generator, suitable for |
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5 * real time generation (current just approx AWGN) |
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6 * |
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7 * Written by Steve Underwood <steveu@coppice.org> |
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8 * |
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9 * Copyright (C) 2005 Steve Underwood |
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10 * |
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11 * All rights reserved. |
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12 * |
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13 * This program is free software; you can redistribute it and/or modify |
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14 * it under the terms of the GNU Lesser General Public License version 2.1, |
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15 * as published by the Free Software Foundation. |
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16 * |
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17 * This program is distributed in the hope that it will be useful, |
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18 * but WITHOUT ANY WARRANTY; without even the implied warranty of |
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19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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20 * GNU Lesser General Public License for more details. |
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21 * |
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22 * You should have received a copy of the GNU Lesser General Public |
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23 * License along with this program; if not, write to the Free Software |
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24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. |
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25 * |
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26 * $Id: noise.h,v 1.17 2009/02/10 13:06:47 steveu Exp $ |
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27 */ |
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28 |
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29 /*! \file */ |
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30 |
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31 #if !defined(_SPANDSP_NOISE_H_) |
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32 #define _SPANDSP_NOISE_H_ |
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33 |
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34 /*! \page noise_page Noise generation |
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35 |
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36 \section noise_page_sec_1 What does it do? |
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37 It generates audio noise. Currently it only generates reasonable quality |
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38 AWGN. It is designed to be of sufficiently low complexity to generate large |
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39 volumes of reasonable quality noise, in real time. |
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40 |
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41 Hoth noise is used to model indoor ambient noise when evaluating communications |
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42 systems such as telephones. It is named after D.F. Hoth, who made the first |
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43 systematic study of this. The official definition of Hoth noise is IEEE |
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44 standard 269-2001 (revised from 269-1992), "Draft Standard Methods for Measuring |
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45 Transmission Performance of Analog and Digital Telephone Sets, Handsets and Headsets." |
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46 |
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47 The table below gives the spectral density of Hoth noise, adjusted in level to produce |
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48 a reading of 50 dBA. |
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49 |
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50 Freq (Hz) Spectral Bandwidth Total power in |
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51 density 10 log_f each 1/3 octave band |
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52 (dB SPL/Hz) (dB) (dB SPL) |
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53 100 32.4 13.5 45.9 |
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54 125 30.9 14.7 45.5 |
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55 160 29.1 15.7 44.9 |
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56 200 27.6 16.5 44.1 |
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57 250 26.0 17.6 43.6 |
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58 315 24.4 18.7 43.1 |
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59 400 22.7 19.7 42.3 |
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60 500 21.1 20.6 41.7 |
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61 630 19.5 21.7 41.2 |
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62 800 17.8 22.7 40.4 |
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63 1000 16.2 23.5 39.7 |
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64 1250 14.6 24.7 39.3 |
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65 1600 12.9 25.7 38.7 |
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66 2000 11.3 26.5 37.8 |
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67 2500 9.6 27.6 37.2 |
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68 3150 7.8 28.7 36.5 |
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69 4000 5.4 29.7 34.8 |
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70 5000 2.6 30.6 33.2 |
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71 6300 -1.3 31.7 30.4 |
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72 8000 -6.6 32.7 26.0 |
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73 |
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74 The tolerance for each 1/3rd octave band is กำ3dB. |
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75 |
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76 \section awgn_page_sec_2 How does it work? |
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77 The central limit theorem says if you add a few random numbers together, |
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78 the result starts to look Gaussian. In this case we sum 8 random numbers. |
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79 The result is fast, and perfectly good as a noise source for many purposes. |
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80 It should not be trusted as a high quality AWGN generator, for elaborate |
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81 modelling purposes. |
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82 */ |
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83 |
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84 enum |
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85 { |
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86 NOISE_CLASS_AWGN = 1, |
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87 NOISE_CLASS_HOTH |
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88 }; |
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89 |
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90 /*! |
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91 Noise generator descriptor. This contains all the state information for an instance |
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92 of the noise generator. |
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93 */ |
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94 typedef struct noise_state_s noise_state_t; |
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95 |
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96 #if defined(__cplusplus) |
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97 extern "C" |
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98 { |
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99 #endif |
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100 |
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101 /*! Initialise an audio noise generator. |
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102 \brief Initialise an audio noise generator. |
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103 \param s The noise generator context. |
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104 \param seed A seed for the underlying random number generator. |
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105 \param level The noise power level in dBmO. |
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106 \param class_of_noise The class of noise (e.g. AWGN). |
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107 \param quality A parameter which permits speed and accuracy of the noise |
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108 generation to be adjusted. |
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109 \return A pointer to the noise generator context. |
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110 */ |
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111 SPAN_DECLARE(noise_state_t *) noise_init_dbm0(noise_state_t *s, int seed, float level, int class_of_noise, int quality); |
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112 |
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113 SPAN_DECLARE(noise_state_t *) noise_init_dbov(noise_state_t *s, int seed, float level, int class_of_noise, int quality); |
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114 |
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115 SPAN_DECLARE(int) noise_release(noise_state_t *s); |
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116 |
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117 SPAN_DECLARE(int) noise_free(noise_state_t *s); |
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118 |
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119 /*! Generate a sample of audio noise. |
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120 \brief Generate a sample of audio noise. |
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121 \param s The noise generator context. |
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122 \return The generated sample. |
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123 */ |
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124 SPAN_DECLARE(int16_t) noise(noise_state_t *s); |
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125 |
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126 #if defined(__cplusplus) |
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127 } |
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128 #endif |
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129 |
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130 #endif |
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131 /*- End of file ------------------------------------------------------------*/ |