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annotate libgsmefr/pre_proc.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 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 }