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/*
** 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: hp50.c *
* *
* Description: *
* 2nd order high pass filter with cut off frequency at 31 Hz. *
* Designed with cheby2 function in MATLAB. *
* Optimized for fixed-point to get the following frequency response: *
* *
* frequency: 0Hz 14Hz 24Hz 31Hz 37Hz 41Hz 47Hz *
* dB loss: -infdB -15dB -6dB -3dB -1.5dB -1dB -0.5dB *
* *
* 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] = {4053, -8106, 4053}; in Q12 *
* Word16 a[3] = {8192, 16211, -8021}; in Q12 *
* *
* float --> b[3] = {0.989501953, -1.979003906, 0.989501953}; *
* a[3] = {1.000000000, 1.978881836, -0.979125977}; *
************************************************************************/
#include "typedef.h"
#include "basic_op.h"
#include "oper_32b.h"
#include "cnst.h"
#include "acelp.h"
/* filter coefficients */
static Word16 b[3] = {4053, -8106, 4053}; /* Q12 */
static Word16 a[3] = {8192, 16211, -8021}; /* Q12 (x2) */
/* Initialization of static values */
void Init_HP50_12k8(Word16 mem[])
{
Set_zero(mem, 6);
}
void HP50_12k8(
Word16 signal[], /* input/output signal */
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 = 8192 ; /* 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 <<= 2; /* 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++ = extract_h((L_add((L_tmp<<1), 0x8000)));
}while(--num !=0);
*mem-- = x1;
*mem-- = x0;
*mem-- = y1_lo;
*mem-- = y1_hi;
*mem-- = y2_lo;
*mem-- = y2_hi;
return;
}
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