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annotate src/int_lpc.c @ 8:8b17df8f6340 default tip

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author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 17 Apr 2024 17:30:25 +0000
parents 56410792419a
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 "typedef.h"
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23 #include "basic_op.h"
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24 #include "count.h"
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25 #include "sig_proc.h"
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26
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27 #define M 10 /* LP order */
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28 #define MP1 11 /* M+1 */
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29
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30 void Int_lpc (
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31 Word16 lsp_old[], /* input : LSP vector at the 4th subframe
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32 of past frame */
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33 Word16 lsp_mid[], /* input : LSP vector at the 2nd subframe
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34 of present frame */
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35 Word16 lsp_new[], /* input : LSP vector at the 4th subframe of
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36 present frame */
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37 Word16 Az[] /* output: interpolated LP parameters in
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38 all subframes */
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39 )
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40 {
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41 Word16 i;
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42 Word16 lsp[M];
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43
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44 /* lsp[i] = lsp_mid[i] * 0.5 + lsp_old[i] * 0.5 */
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45
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46 for (i = 0; i < M; i++)
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47 {
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48 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_old[i], 1));
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49 move16 ();
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50 }
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51
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52 Lsp_Az (lsp, Az); /* Subframe 1 */
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53 Az += MP1; move16 ();
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54
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55 Lsp_Az (lsp_mid, Az); /* Subframe 2 */
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56 Az += MP1; move16 ();
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57
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58 for (i = 0; i < M; i++)
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59 {
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60 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_new[i], 1));
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61 move16 ();
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62 }
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63
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64 Lsp_Az (lsp, Az); /* Subframe 3 */
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65 Az += MP1; move16 ();
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66
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67 Lsp_Az (lsp_new, Az); /* Subframe 4 */
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68
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69 return;
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70 }
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71
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72 /*----------------------------------------------------------------------*
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73 * Function Int_lpc2() *
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74 * ~~~~~~~~~~~~~~~~~~ *
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75 * Interpolation of the LPC parameters. *
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76 * Same as the previous function but we do not recompute Az() for *
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77 * subframe 2 and 4 because it is already available. *
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78 *----------------------------------------------------------------------*/
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79
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80 void Int_lpc2 (
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81 Word16 lsp_old[], /* input : LSP vector at the 4th subframe
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82 of past frame */
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83 Word16 lsp_mid[], /* input : LSP vector at the 2nd subframe
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84 of present frame */
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85 Word16 lsp_new[], /* input : LSP vector at the 4th subframe of
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86 present frame */
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87 Word16 Az[] /* output: interpolated LP parameters
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88 in subframes 1 and 3 */
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89 )
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90 {
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91 Word16 i;
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92 Word16 lsp[M];
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93
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94 /* lsp[i] = lsp_mid[i] * 0.5 + lsp_old[i] * 0.5 */
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95
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96 for (i = 0; i < M; i++)
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97 {
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98 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_old[i], 1));
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99 move16 ();
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100 }
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101 Lsp_Az (lsp, Az); /* Subframe 1 */
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102 Az += MP1 * 2; move16 ();
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103
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104 for (i = 0; i < M; i++)
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105 {
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106 lsp[i] = add (shr (lsp_mid[i], 1), shr (lsp_new[i], 1));
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107 move16 ();
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108 }
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109 Lsp_Az (lsp, Az); /* Subframe 3 */
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110
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111 return;
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112 }