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annotate libgsmefr/int_lpc.c @ 174:d284f2ac087d

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doc/Utils-overview: new RTP utils
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 27 Dec 2022 00:02:28 +0000
parents a0a1e8de4b46
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Int_lpc()
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4 *
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5 * PURPOSE: Interpolates the LSPs and converts to LPC parameters to get
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6 * a different LP filter in each subframe.
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7 *
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8 * DESCRIPTION:
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9 * The 20 ms speech frame is divided into 4 subframes.
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10 * The LSPs are quantized and transmitted at the 2nd and 4th subframes
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11 * (twice per frame) and interpolated at the 1st and 3rd subframe.
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12 *
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13 * |------|------|------|------|
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14 * sf1 sf2 sf3 sf4
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15 * F0 Fm F1
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16 *
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17 * sf1: 1/2 Fm + 1/2 F0 sf3: 1/2 F1 + 1/2 Fm
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18 * sf2: Fm sf4: F1
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19 *
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20 *************************************************************************/
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21
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22 #include "gsm_efr.h"
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23 #include "typedef.h"
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24 #include "namespace.h"
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25 #include "basic_op.h"
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26 #include "no_count.h"
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27 #include "sig_proc.h"
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28 #include "codec.h"
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29
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30 #define M 10 /* LP order */
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31 #define MP1 11 /* M+1 */
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32
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33 void Int_lpc (
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34 Word16 lsp_old[], /* input : LSP vector at the 4th subframe
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35 of past frame */
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36 Word16 lsp_mid[], /* input : LSP vector at the 2nd subframe
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37 of present frame */
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38 Word16 lsp_new[], /* input : LSP vector at the 4th subframe of
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39 present frame */
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40 Word16 Az[] /* output: interpolated LP parameters in
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41 all subframes */
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42 )
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43 {
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44 Word16 i;
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45 Word16 lsp[M];
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46
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47 /* lsp[i] = lsp_mid[i] * 0.5 + lsp_old[i] * 0.5 */
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48
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49 for (i = 0; i < M; i++)
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50 {
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51 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_old[i], 1));
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52 move16 ();
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53 }
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55 Lsp_Az (lsp, Az); /* Subframe 1 */
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56 Az += MP1; move16 ();
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57
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58 Lsp_Az (lsp_mid, Az); /* Subframe 2 */
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59 Az += MP1; move16 ();
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61 for (i = 0; i < M; i++)
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62 {
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63 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_new[i], 1));
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64 move16 ();
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65 }
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67 Lsp_Az (lsp, Az); /* Subframe 3 */
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68 Az += MP1; move16 ();
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69
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70 Lsp_Az (lsp_new, Az); /* Subframe 4 */
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71
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72 return;
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73 }
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74
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75 /*----------------------------------------------------------------------*
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76 * Function Int_lpc2() *
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77 * ~~~~~~~~~~~~~~~~~~ *
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78 * Interpolation of the LPC parameters. *
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79 * Same as the previous function but we do not recompute Az() for *
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80 * subframe 2 and 4 because it is already available. *
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81 *----------------------------------------------------------------------*/
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82
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83 void Int_lpc2 (
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84 Word16 lsp_old[], /* input : LSP vector at the 4th subframe
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85 of past frame */
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86 Word16 lsp_mid[], /* input : LSP vector at the 2nd subframe
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87 of present frame */
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88 Word16 lsp_new[], /* input : LSP vector at the 4th subframe of
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89 present frame */
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90 Word16 Az[] /* output: interpolated LP parameters
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91 in subframes 1 and 3 */
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92 )
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93 {
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94 Word16 i;
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95 Word16 lsp[M];
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96
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97 /* lsp[i] = lsp_mid[i] * 0.5 + lsp_old[i] * 0.5 */
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98
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99 for (i = 0; i < M; i++)
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100 {
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101 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_old[i], 1));
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102 move16 ();
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103 }
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104 Lsp_Az (lsp, Az); /* Subframe 1 */
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105 Az += MP1 * 2; move16 ();
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106
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107 for (i = 0; i < M; i++)
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108 {
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109 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_new[i], 1));
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110 move16 ();
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111 }
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112 Lsp_Az (lsp, Az); /* Subframe 3 */
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113
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114 return;
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115 }