|
2
|
1
|
|
|
2 /******************************************************************
|
|
|
3
|
|
|
4 iLBC Speech Coder ANSI-C Source Code
|
|
|
5
|
|
|
6 anaFilter.c
|
|
|
7
|
|
|
8 Copyright (C) The Internet Society (2004).
|
|
|
9 All Rights Reserved.
|
|
|
10
|
|
|
11 ******************************************************************/
|
|
|
12
|
|
|
13 #include <string.h>
|
|
|
14 #include "iLBC_define.h"
|
|
|
15
|
|
|
16 /*----------------------------------------------------------------*
|
|
|
17 * LP analysis filter.
|
|
|
18 *---------------------------------------------------------------*/
|
|
|
19
|
|
|
20 void anaFilter(float *In, /* (i) Signal to be filtered */
|
|
|
21 float *a, /* (i) LP parameters */
|
|
|
22 int len, /* (i) Length of signal */
|
|
|
23 float *Out, /* (o) Filtered signal */
|
|
|
24 float *mem /* (i/o) Filter state */
|
|
|
25 )
|
|
|
26 {
|
|
|
27 int i, j;
|
|
|
28 float *po, *pi, *pm, *pa;
|
|
|
29
|
|
|
30 po = Out;
|
|
|
31
|
|
|
32 /* Filter first part using memory from past */
|
|
|
33
|
|
|
34 for (i = 0; i < LPC_FILTERORDER; i++) {
|
|
|
35 pi = &In[i];
|
|
|
36 pm = &mem[LPC_FILTERORDER - 1];
|
|
|
37 pa = a;
|
|
|
38 *po = 0.0;
|
|
|
39
|
|
|
40
|
|
|
41
|
|
|
42
|
|
|
43
|
|
|
44 for (j = 0; j <= i; j++) {
|
|
|
45 *po += (*pa++) * (*pi--);
|
|
|
46 }
|
|
|
47 for (j = i + 1; j < LPC_FILTERORDER + 1; j++) {
|
|
|
48
|
|
|
49 *po += (*pa++) * (*pm--);
|
|
|
50 }
|
|
|
51 po++;
|
|
|
52 }
|
|
|
53
|
|
|
54 /* Filter last part where the state is entirely
|
|
|
55 in the input vector */
|
|
|
56
|
|
|
57 for (i = LPC_FILTERORDER; i < len; i++) {
|
|
|
58 pi = &In[i];
|
|
|
59 pa = a;
|
|
|
60 *po = 0.0;
|
|
|
61 for (j = 0; j < LPC_FILTERORDER + 1; j++) {
|
|
|
62 *po += (*pa++) * (*pi--);
|
|
|
63 }
|
|
|
64 po++;
|
|
|
65 }
|
|
|
66
|
|
|
67 /* Update state vector */
|
|
|
68
|
|
|
69 memcpy(mem, &In[len - LPC_FILTERORDER],
|
|
|
70 LPC_FILTERORDER * sizeof(float));
|
|
|
71 }
|
