/* | |
** Copyright 2003-2010, VisualOn, Inc. | |
** | |
** Licensed under the Apache License, Version 2.0 (the "License"); | |
** you may not use this file except in compliance with the License. | |
** You may obtain a copy of the License at | |
** | |
** http://www.apache.org/licenses/LICENSE-2.0 | |
** | |
** Unless required by applicable law or agreed to in writing, software | |
** distributed under the License is distributed on an "AS IS" BASIS, | |
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
** See the License for the specific language governing permissions and | |
** limitations under the License. | |
*/ | |
/*********************************************************************** | |
* File: hp400.c * | |
* * | |
* Description: * | |
* 2nd order high pass filter with cut off frequency at 400 Hz. * | |
* Designed with cheby2 function in MATLAB. * | |
* Optimized for fixed-point to get the following frequency response: * | |
* * | |
* frequency: 0Hz 100Hz 200Hz 300Hz 400Hz 630Hz 1.5kHz 3kHz * | |
* dB loss: -infdB -30dB -20dB -10dB -3dB +6dB +1dB 0dB * | |
* * | |
* Algorithm: * | |
* * | |
* y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2] * | |
* + a[1]*y[i-1] + a[2]*y[i-2]; * | |
* * | |
* Word16 b[3] = {3660, -7320, 3660}; in Q12 * | |
* Word16 a[3] = {4096, 7320, -3540}; in Q12 * | |
* * | |
* float --> b[3] = {0.893554687, -1.787109375, 0.893554687}; * | |
* a[3] = {1.000000000, 1.787109375, -0.864257812}; * | |
* * | |
************************************************************************/ | |
#include "typedef.h" | |
#include "basic_op.h" | |
#include "oper_32b.h" | |
#include "acelp.h" | |
/* filter coefficients */ | |
static Word16 b[3] = {915, -1830, 915}; /* Q12 (/4) */ | |
static Word16 a[3] = {16384, 29280, -14160}; /* Q12 (x4) */ | |
/* Initialization of static values */ | |
void Init_HP400_12k8(Word16 mem[]) | |
{ | |
Set_zero(mem, 6); | |
} | |
void HP400_12k8( | |
Word16 signal[], /* input signal / output is divided by 16 */ | |
Word16 lg, /* lenght of signal */ | |
Word16 mem[] /* filter memory [6] */ | |
) | |
{ | |
Word16 x2; | |
Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1; | |
Word32 L_tmp; | |
Word32 num; | |
y2_hi = *mem++; | |
y2_lo = *mem++; | |
y1_hi = *mem++; | |
y1_lo = *mem++; | |
x0 = *mem++; | |
x1 = *mem; | |
num = (Word32)lg; | |
do | |
{ | |
x2 = x1; | |
x1 = x0; | |
x0 = *signal; | |
/* y[i] = b[0]*x[i] + b[1]*x[i-1] + b140[2]*x[i-2] */ | |
/* + a[1]*y[i-1] + a[2] * y[i-2]; */ | |
L_tmp = 8192L; /* rounding to maximise precision */ | |
L_tmp += y1_lo * a[1]; | |
L_tmp += y2_lo * a[2]; | |
L_tmp = L_tmp >> 14; | |
L_tmp += (y1_hi * a[1] + y2_hi * a[2] + (x0 + x2)* b[0] + x1 * b[1]) << 1; | |
L_tmp <<= 1; /* coeff Q12 --> Q13 */ | |
y2_hi = y1_hi; | |
y2_lo = y1_lo; | |
y1_hi = (Word16)(L_tmp>>16); | |
y1_lo = (Word16)((L_tmp & 0xffff)>>1); | |
/* signal is divided by 16 to avoid overflow in energy computation */ | |
*signal++ = (L_tmp + 0x8000) >> 16; | |
}while(--num !=0); | |
*mem-- = x1; | |
*mem-- = x0; | |
*mem-- = y1_lo; | |
*mem-- = y1_hi; | |
*mem-- = y2_lo; | |
*mem = y2_hi; | |
return; | |
} | |