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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 * line_model.h - Model a telephone line.
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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) 2004 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: line_model.h,v 1.12 2006/10/24 13:45:29 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 /*! \page line_model_page Telephone line model
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31 \section line_model_page_sec_1 What does it do?
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32 The telephone line modelling module provides simple modelling of one way and two
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33 way telephone lines.
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34
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35 The path being modelled is:
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36
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37 - terminal
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38 - | < hybrid echo (2-way models)
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39 - |
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40 - | < noise and filtering
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41 - |
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42 - | < hybrid echo (2-way models)
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43 - CO
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44 - |
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45 - | < A-law distortion + bulk delay
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46 - |
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47 - CO
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48 - | < hybrid echo (2-way models)
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49 - |
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50 - | < noise and filtering
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51 - |
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52 - | < hybrid echo (2-way models)
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53 - terminal
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54 */
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55
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56 #if !defined(_LINE_MODEL_H_)
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57 #define _LINE_MODEL_H_
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58
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59 #define LINE_FILTER_SIZE 129
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60
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61 /*!
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62 One way line model descriptor. This holds the complete state of
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63 a line model with transmission in only one direction.
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64 */
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65 typedef struct
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66 {
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67 codec_munge_state_t *munge;
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68
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69 /*! The coefficients for the near end analogue section simulation filter */
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70 float *near_filter;
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71 /*! The number of coefficients for the near end analogue section simulation filter */
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72 int near_filter_len;
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73 /*! Last transmitted samples (ring buffer, used by the line filter) */
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74 float near_buf[LINE_FILTER_SIZE];
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75 /*! Pointer of the last transmitted sample in buf */
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76 int near_buf_ptr;
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77 /*! The noise source for local analogue section of the line */
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78 awgn_state_t near_noise;
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79
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80 /*! The bulk delay of the path, in samples */
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81 int bulk_delay;
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82 /*! A pointer to the current write position in the bulk delay store. */
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83 int bulk_delay_ptr;
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84 /*! The data store for simulating the bulk delay */
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85 int16_t bulk_delay_buf[8000];
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86
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87 /*! The coefficients for the far end analogue section simulation filter */
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88 float *far_filter;
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89 /*! The number of coefficients for the far end analogue section simulation filter */
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90 int far_filter_len;
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91 /*! Last transmitted samples (ring buffer, used by the line filter) */
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92 float far_buf[LINE_FILTER_SIZE];
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93 /*! Pointer of the last transmitted sample in buf */
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94 int far_buf_ptr;
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95 /*! The noise source for distant analogue section of the line */
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96 awgn_state_t far_noise;
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97
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98 /*! The scaling factor for the local CPE hybrid echo */
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99 float near_cpe_hybrid_echo;
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100 /*! The scaling factor for the local CO hybrid echo */
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101 float near_co_hybrid_echo;
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102
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103 /*! The scaling factor for the far CPE hybrid echo */
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104 float far_cpe_hybrid_echo;
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105 /*! The scaling factor for the far CO hybrid echo */
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106 float far_co_hybrid_echo;
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107 } one_way_line_model_state_t;
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108
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109 /*!
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110 Two way line model descriptor. This holds the complete state of
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111 a line model with transmission in both directions.
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112 */
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113 typedef struct
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114 {
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115 one_way_line_model_state_t line1;
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116 one_way_line_model_state_t line2;
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117 float fout1;
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118 float fout2;
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119 } both_ways_line_model_state_t;
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120
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121 #ifdef __cplusplus
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122 extern "C" {
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123 #endif
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124
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125 void both_ways_line_model(both_ways_line_model_state_t *s,
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126 int16_t *output1,
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127 const int16_t *input1,
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128 int16_t *output2,
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129 const int16_t *input2,
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130 int samples);
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131
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132 both_ways_line_model_state_t *both_ways_line_model_init(int model1,
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133 float noise1,
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134 int model2,
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135 float noise2,
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136 int codec);
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137
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138 int both_ways_line_model_release(both_ways_line_model_state_t *s);
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139
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140 void one_way_line_model(one_way_line_model_state_t *s,
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141 int16_t *output,
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142 const int16_t *input,
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143 int samples);
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144
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145 one_way_line_model_state_t *one_way_line_model_init(int model, float noise, int codec);
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146
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147 int one_way_line_model_release(one_way_line_model_state_t *s);
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148
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149 #ifdef __cplusplus
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150 }
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151 #endif
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152
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153 #endif
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154 /*- End of file ------------------------------------------------------------*/
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