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annotate src/lsp_az.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: Lsp_Az
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4 *
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5 * PURPOSE: Converts from the line spectral pairs (LSP) to
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6 * LP coefficients, for a 10th order filter.
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7 *
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8 * DESCRIPTION:
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9 * - Find the coefficients of F1(z) and F2(z) (see Get_lsp_pol)
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10 * - Multiply F1(z) by 1+z^{-1} and F2(z) by 1-z^{-1}
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11 * - A(z) = ( F1(z) + F2(z) ) / 2
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12 *
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13 *************************************************************************/
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14
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15 #include "typedef.h"
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16 #include "basic_op.h"
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17 #include "oper_32b.h"
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18 #include "count.h"
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19 #include "sig_proc.h"
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20
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21 /* local function */
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22
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23 static void Get_lsp_pol (Word16 *lsp, Word32 *f);
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24
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25 void Lsp_Az (
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26 Word16 lsp[], /* (i) : line spectral frequencies */
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27 Word16 a[] /* (o) : predictor coefficients (order = 10) */
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28 )
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29 {
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30 Word16 i, j;
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31 Word32 f1[6], f2[6];
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32 Word32 t0;
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33
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34 Get_lsp_pol (&lsp[0], f1);
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35 Get_lsp_pol (&lsp[1], f2);
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36
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37 for (i = 5; i > 0; i--)
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38 {
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39 f1[i] = L_add (f1[i], f1[i - 1]); move32 (); /* f1[i] += f1[i-1]; */
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40 f2[i] = L_sub (f2[i], f2[i - 1]); move32 (); /* f2[i] -= f2[i-1]; */
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41 }
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42
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43 a[0] = 4096; move16 ();
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44 for (i = 1, j = 10; i <= 5; i++, j--)
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45 {
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46 t0 = L_add (f1[i], f2[i]); /* f1[i] + f2[i] */
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47 a[i] = extract_l (L_shr_r (t0, 13)); move16 ();
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48 t0 = L_sub (f1[i], f2[i]); /* f1[i] - f2[i] */
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49 a[j] = extract_l (L_shr_r (t0, 13)); move16 ();
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50 }
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51
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52 return;
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53 }
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54
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55 /*************************************************************************
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56 *
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57 * FUNCTION: Get_lsp_pol
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58 *
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59 * PURPOSE: Find the polynomial F1(z) or F2(z) from the LSPs.
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60 * If the LSP vector is passed at address 0 F1(z) is computed
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61 * and if it is passed at address 1 F2(z) is computed.
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62 *
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63 * DESCRIPTION:
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64 * This is performed by expanding the product polynomials:
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65 *
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66 * F1(z) = product ( 1 - 2 lsp[i] z^-1 + z^-2 )
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67 * i=0,2,4,6,8
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68 * F2(z) = product ( 1 - 2 lsp[i] z^-1 + z^-2 )
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69 * i=1,3,5,7,9
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70 *
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71 * where lsp[] is the LSP vector in the cosine domain.
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72 *
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73 * The expansion is performed using the following recursion:
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74 *
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75 * f[0] = 1
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76 * b = -2.0 * lsp[0]
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77 * f[1] = b
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78 * for i=2 to 5 do
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79 * b = -2.0 * lsp[2*i-2];
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80 * f[i] = b*f[i-1] + 2.0*f[i-2];
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81 * for j=i-1 down to 2 do
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82 * f[j] = f[j] + b*f[j-1] + f[j-2];
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83 * f[1] = f[1] + b;
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84 *
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85 *************************************************************************/
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86
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87 static void Get_lsp_pol (Word16 *lsp, Word32 *f)
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88 {
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89 Word16 i, j, hi, lo;
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90 Word32 t0;
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91
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92 /* f[0] = 1.0; */
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93 *f = L_mult (4096, 2048); move32 ();
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94 f++; move32 ();
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95 *f = L_msu ((Word32) 0, *lsp, 512); /* f[1] = -2.0 * lsp[0]; */
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96 f++; move32 ();
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97 lsp += 2; /* Advance lsp pointer */
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98
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99 for (i = 2; i <= 5; i++)
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100 {
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101 *f = f[-2]; move32 ();
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102
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103 for (j = 1; j < i; j++, f--)
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104 {
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105 L_Extract (f[-1], &hi, &lo);
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106 t0 = Mpy_32_16 (hi, lo, *lsp); /* t0 = f[-1] * lsp */
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107 t0 = L_shl (t0, 1);
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108 *f = L_add (*f, f[-2]); move32 (); /* *f += f[-2] */
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109 *f = L_sub (*f, t0);move32 (); /* *f -= t0 */
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110 }
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111 *f = L_msu (*f, *lsp, 512); move32 (); /* *f -= lsp<<9 */
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112 f += i; /* Advance f pointer */
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113 lsp += 2; /* Advance lsp pointer */
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114 }
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115
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116 return;
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117 }