annotate libgsmefr/pre_proc.c @ 555:62943a1ad64e

doc/FR1-Rx-DTX-detail: grammar fix
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 11 Oct 2024 00:22:47 +0000
parents 3ea19a9aa2a1
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Pre_Process()
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4 *
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5 * PURPOSE: Preprocessing of input speech.
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6 *
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7 * DESCRIPTION:
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8 * - 2nd order high pass filtering with cut off frequency at 80 Hz.
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9 * - Divide input by two.
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10 *
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11 *************************************************************************/
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12
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13 #include "gsm_efr.h"
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14 #include "typedef.h"
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15 #include "namespace.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 "no_count.h"
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19 #include "sig_proc.h"
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20 #include "cnst.h"
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21 #include "enc_state.h"
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22
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23 /*------------------------------------------------------------------------*
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24 * *
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25 * Algorithm: *
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26 * *
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27 * y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b[2]*x[i-2]/2 *
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28 * + a[1]*y[i-1] + a[2]*y[i-2]; *
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29 * *
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30 * *
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31 * Input is divided by two in the filtering process. *
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32 *------------------------------------------------------------------------*/
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33
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34 /* filter coefficients (fc = 80 Hz, coeff. b[] is divided by 2) */
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36 static const Word16 b[3] = {1899, -3798, 1899};
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37 static const Word16 a[3] = {4096, 7807, -3733};
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38
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39 /* Initialization of static values */
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41 void Init_Pre_Process (struct EFR_encoder_state *st)
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42 {
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43 struct preproc_state *pps = &st->pre_proc;
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45 pps->y2_hi = 0;
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46 pps->y2_lo = 0;
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47 pps->y1_hi = 0;
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48 pps->y1_lo = 0;
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49 pps->x0 = 0;
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50 pps->x1 = 0;
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51 }
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53 void Pre_Process (
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54 struct EFR_encoder_state *st,
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55 Word16 signal[], /* input/output signal */
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56 Word16 lg) /* lenght of signal */
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57 {
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58 struct preproc_state *pps = &st->pre_proc;
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59 Word16 i, x2;
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60 Word32 L_tmp;
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62 for (i = 0; i < lg; i++)
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63 {
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64 x2 = pps->x1;
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65 pps->x1 = pps->x0;
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66 pps->x0 = signal[i];
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68 /* y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b140[2]*x[i-2]/2 */
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69 /* + a[1]*y[i-1] + a[2] * y[i-2]; */
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70
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71 L_tmp = Mpy_32_16 (pps->y1_hi, pps->y1_lo, a[1]);
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72 L_tmp = L_add (L_tmp, Mpy_32_16 (pps->y2_hi, pps->y2_lo, a[2]));
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73 L_tmp = L_mac (L_tmp, pps->x0, b[0]);
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74 L_tmp = L_mac (L_tmp, pps->x1, b[1]);
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75 L_tmp = L_mac (L_tmp, x2, b[2]);
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76 L_tmp = L_shl (L_tmp, 3);
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77 signal[i] = round (L_tmp);
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78
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79 pps->y2_hi = pps->y1_hi;
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80 pps->y2_lo = pps->y1_lo;
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81 L_Extract (L_tmp, &pps->y1_hi, &pps->y1_lo);
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82 }
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83 return;
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84 }