hp6k.c

通讯协议

/*-------------------------------------------------------------------*
 *                         HP6K.C									 *
 *-------------------------------------------------------------------*
 * 15th order band pass 6kHz to 7kHz FIR filter.                     *
 *                                                                   *
 * frequency:  4kHz   5kHz  5.5kHz  6kHz  6.5kHz 7kHz  7.5kHz  8kHz  *
 * dB loss:   -60dB  -45dB  -13dB   -3dB   0dB   -3dB  -13dB  -45dB  *
 *-------------------------------------------------------------------*/

#include "typedef.h"
#include "basic_op.h"
#include "acelp.h"
#include "count.h"
#include "cnst.h"

#define L_FIR 31

/* filter coefficients (gain=4.0) */

static Word16 fir_6k_7k[L_FIR] =
{
    -32, 47, 32, -27, -369,
    1122, -1421, 0, 3798, -8880,
    12349, -10984, 3548, 7766, -18001,
    22118, -18001, 7766, 3548, -10984,
    12349, -8880, 3798, 0, -1421,
    1122, -369, -27, 32, 47,
    -32
};


void Init_Filt_6k_7k(Word16 mem[])         /* mem[30] */
{
    Set_zero(mem, L_FIR - 1);

    return;
}

void Filt_6k_7k(
     Word16 signal[],                      /* input:  signal                  */
     Word16 lg,                            /* input:  length of input         */
     Word16 mem[]                          /* in/out: memory (size=30)        */
)
{
    Word16 i, j, x[L_SUBFR16k + (L_FIR - 1)];
    Word32 L_tmp;

    Copy(mem, x, L_FIR - 1);

    for (i = 0; i < lg; i++)
    {
        x[i + L_FIR - 1] = shr(signal[i], 2);   move16();  /* gain of filter = 4 */
    }

    for (i = 0; i < lg; i++)
    {
        L_tmp = 0;                         move32();
        for (j = 0; j < L_FIR; j++)
            L_tmp = L_mac(L_tmp, x[i + j], fir_6k_7k[j]);
        signal[i] = round(L_tmp);          move16();
    }

    Copy(x + lg, mem, L_FIR - 1);

    return;
}