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2 /******************************************************************
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3
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4 iLBC Speech Coder ANSI-C Source Code
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6 lsf.c
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7
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8 Copyright (C) The Internet Society (2004).
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9 All Rights Reserved.
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10
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11 ******************************************************************/
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12
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13 #include <string.h>
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14
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17
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18
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19 #include <math.h>
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20
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21 #include "iLBC_define.h"
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22
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23 /*----------------------------------------------------------------*
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24 * conversion from lpc coefficients to lsf coefficients
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25 *---------------------------------------------------------------*/
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26
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27 void a2lsf(float *freq, /* (o) lsf coefficients */
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28 float *a /* (i) lpc coefficients */
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29 )
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30 {
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31 float steps[LSF_NUMBER_OF_STEPS] =
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32 { (float) 0.00635, (float) 0.003175, (float) 0.0015875,
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33 (float) 0.00079375
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34 };
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35 float step;
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36 int step_idx;
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37 int lsp_index;
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38 float p[LPC_HALFORDER];
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39 float q[LPC_HALFORDER];
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40 float p_pre[LPC_HALFORDER];
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41 float q_pre[LPC_HALFORDER];
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42 float old_p, old_q, *old;
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43 float *pq_coef;
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44 float omega, old_omega;
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45 int i;
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46 float hlp, hlp1, hlp2, hlp3, hlp4, hlp5;
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47
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48 for (i = 0; i < LPC_HALFORDER; i++) {
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49 p[i] = (float) -1.0 * (a[i + 1] + a[LPC_FILTERORDER - i]);
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50 q[i] = a[LPC_FILTERORDER - i] - a[i + 1];
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51 }
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52
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53 p_pre[0] = (float) -1.0 - p[0];
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54 p_pre[1] = -p_pre[0] - p[1];
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55 p_pre[2] = -p_pre[1] - p[2];
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56 p_pre[3] = -p_pre[2] - p[3];
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57 p_pre[4] = -p_pre[3] - p[4];
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58 p_pre[4] = p_pre[4] / 2;
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59
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60 q_pre[0] = (float) 1.0 - q[0];
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61 q_pre[1] = q_pre[0] - q[1];
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62 q_pre[2] = q_pre[1] - q[2];
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63 q_pre[3] = q_pre[2] - q[3];
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64 q_pre[4] = q_pre[3] - q[4];
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65 q_pre[4] = q_pre[4] / 2;
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66
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67 omega = 0.0;
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68
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69
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70
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71
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72
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73 old_omega = 0.0;
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74
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75 old_p = FLOAT_MAX;
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76 old_q = FLOAT_MAX;
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77
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78 /* Here we loop through lsp_index to find all the
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79 LPC_FILTERORDER roots for omega. */
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80
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81 for (lsp_index = 0; lsp_index < LPC_FILTERORDER; lsp_index++) {
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82
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83 /* Depending on lsp_index being even or odd, we
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84 alternatively solve the roots for the two LSP equations. */
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85
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86
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87 if ((lsp_index & 0x1) == 0) {
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88 pq_coef = p_pre;
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89 old = &old_p;
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90 } else {
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91 pq_coef = q_pre;
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92 old = &old_q;
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93 }
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94
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95 /* Start with low resolution grid */
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96
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97 for (step_idx = 0, step = steps[step_idx];
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98 step_idx < LSF_NUMBER_OF_STEPS;) {
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99
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100 /* cos(10piw) + pq(0)cos(8piw) + pq(1)cos(6piw) +
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101 pq(2)cos(4piw) + pq(3)cod(2piw) + pq(4) */
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102
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103 hlp = (float) cos(omega * TWO_PI);
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104 hlp1 = (float) 2.0 *hlp + pq_coef[0];
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105 hlp2 = (float) 2.0 *hlp * hlp1 - (float) 1.0 + pq_coef[1];
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106 hlp3 = (float) 2.0 *hlp * hlp2 - hlp1 + pq_coef[2];
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107 hlp4 = (float) 2.0 *hlp * hlp3 - hlp2 + pq_coef[3];
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108 hlp5 = hlp * hlp4 - hlp3 + pq_coef[4];
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109
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110
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111 if (((hlp5 * (*old)) <= 0.0) || (omega >= 0.5)) {
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112
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113 if (step_idx == (LSF_NUMBER_OF_STEPS - 1)) {
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114
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115 if (fabs(hlp5) >= fabs(*old)) {
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116 freq[lsp_index] = omega - step;
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117 } else {
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118 freq[lsp_index] = omega;
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119 }
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120
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121
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122
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123
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124
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125
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126
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127 if ((*old) >= 0.0) {
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128 *old = (float) -1.0 * FLOAT_MAX;
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129 } else {
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130 *old = FLOAT_MAX;
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131 }
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132
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133 omega = old_omega;
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134 step_idx = 0;
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135
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136 step_idx = LSF_NUMBER_OF_STEPS;
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137 } else {
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138
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139 if (step_idx == 0) {
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140 old_omega = omega;
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141 }
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142
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143 step_idx++;
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144 omega -= steps[step_idx];
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145
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146 /* Go back one grid step */
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147
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148 step = steps[step_idx];
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149 }
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150 } else {
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151
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152 /* increment omega until they are of different sign,
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153 and we know there is at least one root between omega
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154 and old_omega */
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155 *old = hlp5;
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156 omega += step;
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157 }
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158 }
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159 }
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160
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161 for (i = 0; i < LPC_FILTERORDER; i++) {
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162 freq[i] = freq[i] * TWO_PI;
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163 }
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164 }
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165
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166 /*----------------------------------------------------------------*
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167 * conversion from lsf coefficients to lpc coefficients
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168 *---------------------------------------------------------------*/
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169
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170 void lsf2a(float *a_coef, /* (o) lpc coefficients */
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171 float *freq /* (i) lsf coefficients */
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172 )
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173 {
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174 int i, j;
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175 float hlp;
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176 float p[LPC_HALFORDER], q[LPC_HALFORDER];
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177 float a[LPC_HALFORDER + 1], a1[LPC_HALFORDER], a2[LPC_HALFORDER];
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178 float b[LPC_HALFORDER + 1], b1[LPC_HALFORDER], b2[LPC_HALFORDER];
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179
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180 for (i = 0; i < LPC_FILTERORDER; i++) {
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181 freq[i] = freq[i] * PI2;
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182 }
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183
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184 /* Check input for ill-conditioned cases. This part is not
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185 found in the TIA standard. It involves the following 2 IF
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186 blocks. If "freq" is judged ill-conditioned, then we first
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187 modify freq[0] and freq[LPC_HALFORDER-1] (normally
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188 LPC_HALFORDER = 10 for LPC applications), then we adjust
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189 the other "freq" values slightly */
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190
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191
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192 if ((freq[0] <= 0.0) || (freq[LPC_FILTERORDER - 1] >= 0.5)) {
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193
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194
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195 if (freq[0] <= 0.0) {
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196 freq[0] = (float) 0.022;
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197 }
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198
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199
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200 if (freq[LPC_FILTERORDER - 1] >= 0.5) {
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201 freq[LPC_FILTERORDER - 1] = (float) 0.499;
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202 }
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203
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204 hlp = (freq[LPC_FILTERORDER - 1] - freq[0]) /
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205 (float) (LPC_FILTERORDER - 1);
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206
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207 for (i = 1; i < LPC_FILTERORDER; i++) {
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208 freq[i] = freq[i - 1] + hlp;
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209 }
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210 }
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211
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212 memset(a1, 0, LPC_HALFORDER * sizeof(float));
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213 memset(a2, 0, LPC_HALFORDER * sizeof(float));
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214 memset(b1, 0, LPC_HALFORDER * sizeof(float));
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215 memset(b2, 0, LPC_HALFORDER * sizeof(float));
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216 memset(a, 0, (LPC_HALFORDER + 1) * sizeof(float));
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217 memset(b, 0, (LPC_HALFORDER + 1) * sizeof(float));
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218
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219
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220
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221
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222
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223
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224 /* p[i] and q[i] compute cos(2*pi*omega_{2j}) and
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225 cos(2*pi*omega_{2j-1} in eqs. 4.2.2.2-1 and 4.2.2.2-2.
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226 Note that for this code p[i] specifies the coefficients
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227 used in .Q_A(z) while q[i] specifies the coefficients used
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228 in .P_A(z) */
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229
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230 for (i = 0; i < LPC_HALFORDER; i++) {
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231 p[i] = (float) cos(TWO_PI * freq[2 * i]);
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232 q[i] = (float) cos(TWO_PI * freq[2 * i + 1]);
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233 }
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234
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235 a[0] = 0.25;
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236 b[0] = 0.25;
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237
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238 for (i = 0; i < LPC_HALFORDER; i++) {
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239 a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
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240 b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
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241 a2[i] = a1[i];
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242 a1[i] = a[i];
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243 b2[i] = b1[i];
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244 b1[i] = b[i];
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245 }
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246
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247 for (j = 0; j < LPC_FILTERORDER; j++) {
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248
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249 if (j == 0) {
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250 a[0] = 0.25;
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251 b[0] = -0.25;
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252 } else {
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253 a[0] = b[0] = 0.0;
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254 }
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255
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256 for (i = 0; i < LPC_HALFORDER; i++) {
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257 a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
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258 b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
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259 a2[i] = a1[i];
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260 a1[i] = a[i];
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261 b2[i] = b1[i];
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262 b1[i] = b[i];
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263 }
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264
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265 a_coef[j + 1] = 2 * (a[LPC_HALFORDER] + b[LPC_HALFORDER]);
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266 }
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267
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268 a_coef[0] = 1.0;
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269 }
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