hp400.c revision 41050cdb033641ddf26831d9272c0930f7b40a2d 
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  */
47static Word16 b[3] = {915, -1830, 915};         /* Q12 (/4) */
48static Word16 a[3] = {16384, 29280, -14160};    /* Q12 (x4) */
49/* Initialization of static values */
50
51void Init_HP400_12k8(Word16 mem[])
52{
53	Set_zero(mem, 6);
54}
55
56
57void 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
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107