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annotate libgsmefr/int_lpc.c @ 183:452c1d5a6268

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libgsmefr BFI w/o data: emit zero output after decoder reset In real-life usage, each EFR decoder session will most likely begin with lots of BFI frames before the first real frame arrives. However, because the spec-defined home state of the decoder is speech rather than CN, our regular logic for BFI w/o data would have to feed pseudorandom noise to the decoder (in the "fixed codebook excitation pulses" part), which is silly to do at the beginning of the decoder session right out of reset. Therefore, let's check reset_flag_old, and if we are still in the reset state, simply emit zero output.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 03 Jan 2023 00:12:18 +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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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 }