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: hp400.c *
19 * *
20 * Description: *
21 * 2nd order high pass filter with cut off frequency at 400 Hz. *
22 * Designed with cheby2 function in MATLAB. *
23 * Optimized for fixed-point to get the following frequency response: *
24 * *
25 * frequency: 0Hz 100Hz 200Hz 300Hz 400Hz 630Hz 1.5kHz 3kHz *
26 * dB loss: -infdB -30dB -20dB -10dB -3dB +6dB +1dB 0dB *
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] = {3660, -7320, 3660}; in Q12 *
34 * Word16 a[3] = {4096, 7320, -3540}; in Q12 *
35 * *
36 * float --> b[3] = {0.893554687, -1.787109375, 0.893554687}; *
37 * a[3] = {1.000000000, 1.787109375, -0.864257812}; *
38 * *
39 ************************************************************************/
40
41 #include "typedef.h"
42 #include "basic_op.h"
43 #include "oper_32b.h"
44 #include "acelp.h"
45
46 /* filter coefficients */
47 static Word16 b[3] = {915, -1830, 915}; /* Q12 (/4) */
48 static Word16 a[3] = {16384, 29280, -14160}; /* Q12 (x4) */
49 /* Initialization of static values */
50
Init_HP400_12k8(Word16 mem[])51 void Init_HP400_12k8(Word16 mem[])
52 {
53 Set_zero(mem, 6);
54 }
55
56
HP400_12k8(Word16 signal[],Word16 lg,Word16 mem[])57 void HP400_12k8(
58 Word16 signal[], /* input signal / output is divided by 16 */
59 Word16 lg, /* lenght of signal */
60 Word16 mem[] /* filter memory [6] */
61 )
62 {
63 Word16 x2;
64 Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
65 Word32 L_tmp;
66 Word32 num;
67 y2_hi = *mem++;
68 y2_lo = *mem++;
69 y1_hi = *mem++;
70 y1_lo = *mem++;
71 x0 = *mem++;
72 x1 = *mem;
73 num = (Word32)lg;
74 do
75 {
76 x2 = x1;
77 x1 = x0;
78 x0 = *signal;
79 /* y[i] = b[0]*x[i] + b[1]*x[i-1] + b140[2]*x[i-2] */
80 /* + a[1]*y[i-1] + a[2] * y[i-2]; */
81 L_tmp = 8192L; /* rounding to maximise precision */
82 L_tmp += y1_lo * a[1];
83 L_tmp += y2_lo * a[2];
84 L_tmp = L_tmp >> 14;
85 L_tmp += (y1_hi * a[1] + y2_hi * a[2] + (x0 + x2)* b[0] + x1 * b[1]) << 1;
86 L_tmp <<= 1; /* coeff Q12 --> Q13 */
87 y2_hi = y1_hi;
88 y2_lo = y1_lo;
89 y1_hi = (Word16)(L_tmp>>16);
90 y1_lo = (Word16)((L_tmp & 0xffff)>>1);
91
92 /* signal is divided by 16 to avoid overflow in energy computation */
93 *signal++ = (L_tmp + 0x8000) >> 16;
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 return;
103 }
104
105
106
107