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comparison libgsmefr/pre_proc.c @ 53:49dd1ac8e75b

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libgsmefr: import most *.c files from ETSI source
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 25 Nov 2022 16:18:21 +0000
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children 3ea19a9aa2a1
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52:988fd7ff514f 53:49dd1ac8e75b
1 /*************************************************************************
2 *
3 * FUNCTION: Pre_Process()
4 *
5 * PURPOSE: Preprocessing of input speech.
6 *
7 * DESCRIPTION:
8 * - 2nd order high pass filtering with cut off frequency at 80 Hz.
9 * - Divide input by two.
10 *
11 *************************************************************************/
12
13 #include "typedef.h"
14 #include "basic_op.h"
15 #include "oper_32b.h"
16 #include "count.h"
17
18 /*------------------------------------------------------------------------*
19 * *
20 * Algorithm: *
21 * *
22 * y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b[2]*x[i-2]/2 *
23 * + a[1]*y[i-1] + a[2]*y[i-2]; *
24 * *
25 * *
26 * Input is divided by two in the filtering process. *
27 *------------------------------------------------------------------------*/
28
29 /* filter coefficients (fc = 80 Hz, coeff. b[] is divided by 2) */
30
31 static const Word16 b[3] = {1899, -3798, 1899};
32 static const Word16 a[3] = {4096, 7807, -3733};
33
34 /* Static values to be preserved between calls */
35 /* y[] values are kept in double precision */
36
37 static Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
38
39 /* Initialization of static values */
40
41 void Init_Pre_Process (void)
42 {
43 y2_hi = 0;
44 y2_lo = 0;
45 y1_hi = 0;
46 y1_lo = 0;
47 x0 = 0;
48 x1 = 0;
49 }
50
51 void Pre_Process (
52 Word16 signal[], /* input/output signal */
53 Word16 lg) /* lenght of signal */
54 {
55 Word16 i, x2;
56 Word32 L_tmp;
57
58 for (i = 0; i < lg; i++)
59 {
60 x2 = x1; move16 ();
61 x1 = x0; move16 ();
62 x0 = signal[i]; move16 ();
63
64 /* y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b140[2]*x[i-2]/2 */
65 /* + a[1]*y[i-1] + a[2] * y[i-2]; */
66
67 L_tmp = Mpy_32_16 (y1_hi, y1_lo, a[1]);
68 L_tmp = L_add (L_tmp, Mpy_32_16 (y2_hi, y2_lo, a[2]));
69 L_tmp = L_mac (L_tmp, x0, b[0]);
70 L_tmp = L_mac (L_tmp, x1, b[1]);
71 L_tmp = L_mac (L_tmp, x2, b[2]);
72 L_tmp = L_shl (L_tmp, 3);
73 signal[i] = round (L_tmp); move16 ();
74
75 y2_hi = y1_hi; move16 ();
76 y2_lo = y1_lo; move16 ();
77 L_Extract (L_tmp, &y1_hi, &y1_lo);
78 }
79 return;
80 }