ref: 94c7cb322517928839dde6a263783b773e2629c3
dir: /amr-wb/hp400.c/
/*-----------------------------------------------------------------------*
* HP400.C *
*-----------------------------------------------------------------------*
* 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"
#include "count.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 i, x2;
Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
Word32 L_tmp;
y2_hi = mem[0]; move16();
y2_lo = mem[1]; move16();
y1_hi = mem[2]; move16();
y1_lo = mem[3]; move16();
x0 = mem[4]; move16();
x1 = mem[5]; move16();
for (i = 0; i < lg; i++)
{
x2 = x1; move16();
x1 = x0; move16();
x0 = signal[i]; move16();
/* 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]; */
move32();
L_tmp = 16384L; /* rounding to maximise precision */
L_tmp = L_mac(L_tmp, y1_lo, a[1]);
L_tmp = L_mac(L_tmp, y2_lo, a[2]);
L_tmp = L_shr(L_tmp, 15);
L_tmp = L_mac(L_tmp, y1_hi, a[1]);
L_tmp = L_mac(L_tmp, y2_hi, a[2]);
L_tmp = L_mac(L_tmp, x0, b[0]);
L_tmp = L_mac(L_tmp, x1, b[1]);
L_tmp = L_mac(L_tmp, x2, b[2]);
L_tmp = L_shl(L_tmp, 1); /* coeff Q12 --> Q13 */
y2_hi = y1_hi; move16();
y2_lo = y1_lo; move16();
L_Extract(L_tmp, &y1_hi, &y1_lo);
/* signal is divided by 16 to avoid overflow in energy computation */
signal[i] = round(L_tmp); move16();
}
mem[0] = y2_hi; move16();
mem[1] = y2_lo; move16();
mem[2] = y1_hi; move16();
mem[3] = y1_lo; move16();
mem[4] = x0; move16();
mem[5] = x1; move16();
return;
}