pre_proc.c

语音压缩编码中的g729p编码程序

/*
   ITU-T G.729 Annex C - Reference C code for floating point
                         implementation of G.729
                         Version 1.01 of 15.September.98
*/

/*
----------------------------------------------------------------------
                    COPYRIGHT NOTICE
----------------------------------------------------------------------
   ITU-T G.729 Annex C ANSI C source code
   Copyright (C) 1998, AT&T, France Telecom, NTT, University of
   Sherbrooke.  All rights reserved.

----------------------------------------------------------------------
*/

/*
 File : PRE_PROC.C
*/


/*------------------------------------------------------------------------*
 * Function pre_process()                                                 *
 *                                                                        *
 * Preprocessing of input speech.                                         *
 *   - 2nd order high pass filter with cut off frequency at 140 Hz.       *
 *-----------------------------------------------------------------------*/

#include "typedef.h"
#include "ld8k.h"
#include "tab_ld8k.h"

 /*------------------------------------------------------------------------*
 * 2nd order high pass filter with cut off frequency at 140 Hz.           *
 * Designed with SPPACK efi command -40 dB att, 0.25 ri.                  *
 *                                                                        *
 * 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];                         *
 *                                                                        *
 *     b[3] = {0.92727435E+00, -0.18544941E+01, 0.92727435E+00};          *
 *     a[3] = {0.10000000E+01, 0.19059465E+01, -0.91140240E+00};          *
*-----------------------------------------------------------------------*/


static FLOAT x0, x1;         /* high-pass fir memory          */
static FLOAT y1, y2;         /* high-pass iir memory          */

void init_pre_process( void
                                          )
{
        x0 = x1 = (F)0.0;
        y2 = y1 = (F)0.0;
        
        return;
}

void pre_process(
                                 FLOAT signal[],      /* (i/o)  : signal                     */
                                 int lg               /* (i)    : lenght of signal           */
                                 )
{
        int i;
        FLOAT x2;
        FLOAT y0;
        
        for(i=0; i<lg; i++)
        {
                x2 = x1;
                x1 = x0;
                x0 = signal[i];
                
                y0 = y1*a140[1] + y2*a140[2] + x0*b140[0] + x1*b140[1] + x2*b140[2];
                
                signal[i] = y0;
                y2 = y1;
                y1 = y0;
        }
        
        return;
}