1 /*
2 ** Copyright 2003-2010, VisualOn, Inc.
3 **
4 ** Licensed under the Apache License, Version 2.0 (the "License");
5 ** you may not use this file except in compliance with the License.
6 ** You may obtain a copy of the License at
7 **
8 ** http://www.apache.org/licenses/LICENSE-2.0
9 **
10 ** Unless required by applicable law or agreed to in writing, software
11 ** distributed under the License is distributed on an "AS IS" BASIS,
12 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 ** See the License for the specific language governing permissions and
14 ** limitations under the License.
15 */
16
17 /***********************************************************************
18 * File: hp50.c *
19 * *
20 * Description: *
21 * 2nd order high pass filter with cut off frequency at 31 Hz. *
22 * Designed with cheby2 function in MATLAB. *
23 * Optimized for fixed-point to get the following frequency response: *
24 * *
25 * frequency: 0Hz 14Hz 24Hz 31Hz 37Hz 41Hz 47Hz *
26 * dB loss: -infdB -15dB -6dB -3dB -1.5dB -1dB -0.5dB *
27 * *
28 * Algorithm: *
29 * *
30 * y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2] *
31 * + a[1]*y[i-1] + a[2]*y[i-2]; *
32 * *
33 * Word16 b[3] = {4053, -8106, 4053}; in Q12 *
34 * Word16 a[3] = {8192, 16211, -8021}; in Q12 *
35 * *
36 * float --> b[3] = {0.989501953, -1.979003906, 0.989501953}; *
37 * a[3] = {1.000000000, 1.978881836, -0.979125977}; *
38 ************************************************************************/
39
40 #include "typedef.h"
41 #include "basic_op.h"
42 #include "oper_32b.h"
43 #include "cnst.h"
44 #include "acelp.h"
45
46 /* filter coefficients */
47 static Word16 b[3] = {4053, -8106, 4053}; /* Q12 */
48 static Word16 a[3] = {8192, 16211, -8021}; /* Q12 (x2) */
49
50 /* Initialization of static values */
51
Init_HP50_12k8(Word16 mem[])52 void Init_HP50_12k8(Word16 mem[])
53 {
54 Set_zero(mem, 6);
55 }
56
57
HP50_12k8(Word16 signal[],Word16 lg,Word16 mem[])58 void HP50_12k8(
59 Word16 signal[], /* input/output signal */
60 Word16 lg, /* lenght of signal */
61 Word16 mem[] /* filter memory [6] */
62 )
63 {
64 Word16 x2;
65 Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
66 Word32 L_tmp;
67 Word32 num;
68
69 y2_hi = *mem++;
70 y2_lo = *mem++;
71 y1_hi = *mem++;
72 y1_lo = *mem++;
73 x0 = *mem++;
74 x1 = *mem;
75 num = (Word32)lg;
76 do
77 {
78 x2 = x1;
79 x1 = x0;
80 x0 = *signal;
81 /* y[i] = b[0]*x[i] + b[1]*x[i-1] + b140[2]*x[i-2] */
82 /* + a[1]*y[i-1] + a[2] * y[i-2]; */
83 L_tmp = 8192 ; /* rounding to maximise precision */
84 L_tmp += y1_lo * a[1];
85 L_tmp += y2_lo * a[2];
86 L_tmp = L_tmp >> 14;
87 L_tmp += (y1_hi * a[1] + y2_hi * a[2] + (x0 + x2) * b[0] + x1 * b[1]) << 1;
88 L_tmp <<= 2; /* coeff Q12 --> Q13 */
89 y2_hi = y1_hi;
90 y2_lo = y1_lo;
91 y1_hi = (Word16)(L_tmp>>16);
92 y1_lo = (Word16)((L_tmp & 0xffff)>>1);
93 *signal++ = extract_h((L_add((L_tmp<<1), 0x8000)));
94 }while(--num !=0);
95
96 *mem-- = x1;
97 *mem-- = x0;
98 *mem-- = y1_lo;
99 *mem-- = y1_hi;
100 *mem-- = y2_lo;
101 *mem-- = y2_hi;
102
103 return;
104 }
105
106
107