pre_proc.c

g729a 语音编码,再linux c 环境下实现,有非常的好的移植性,通话质量好

/*
   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
 Used for the floating point version of both
 G.729 main body and G.729A
*/


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

#include "typedef.h"
#include "version.h"
#ifdef VER_G729A
 #include "ld8a.h"
 #include "tab_ld8a.h"
#else
 #include "ld8k.h"
 #include "tab_ld8k.h"
#endif

/*------------------------------------------------------------------------*
 * 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;
}