lsptopc.c

语音CELP压缩解压源代码（C语音)

/**************************************************************************
*
* NAME
*	lsptopc 
*
* FUNCTION
*
*	convert lsp frequencies to predictor coefficients
*
* SYNOPSIS
*
*	subroutine lsptopc(f, pc)
*
*   formal
*			data	I/O
*	name		type	type	function
*	-------------------------------------------------------------------
*	f		real	i	lsp frequencies
*	pc		real	o	LPC predictor coefficients
*
*   external
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*	no		int	i
*	frame		int	i
*
***************************************************************************
*
* DESCRIPTION
*
*	LSPTOPC converts line spectral frequencies to LPC predictor
*	coefficients.
*
*	The analysis filter may be reconstructed:
*
*		A(z) = 1/2 [ P(z) + Q(z) ]
*
*	CELP's LPC predictor coefficient convention is:
*              p+1         -(i-1)
*       A(z) = SUM   a   z          where a  = +1.0
*              i=1    i                    1
*
***************************************************************************
*
* CALLED BY
*
*	celp	spectdist   intsynth
*
* CALLS
*
*
*
**************************************************************************/
#define	TRUE	1
#define	FALSE	0
#include <math.h>
#include <stdio.h>
#include "ccsub.h"
extern int no, frame;

lsptopc(f, pc)
float f[], pc[];

{
  int i, j, k, noh, lspflag;
  float freq[MAXNO], p[MAXNO / 2], q[MAXNO / 2];
  float a[MAXNO / 2 + 1], a1[MAXNO / 2 + 1], a2[MAXNO / 2 + 1];
  float b[MAXNO / 2 + 1], b1[MAXNO / 2 + 1], b2[MAXNO / 2 + 1];
  float pi, xx, xf;

  /* *check input for ill-conditioned cases 			 */

  if (f[0] <= 0.0 || f[0] >= 0.5)
    printf("lsptopc: LSPs out of bounds; f(0) = %f at frame %d\n",
	   f[0], frame);
  lspflag = FALSE;
  for (i = 1; i < no; i++)
  {
    if (f[i] <= f[i - 1])
      lspflag = TRUE;
    if (f[i] <= 0.0 || f[i] >= 0.5)
      printf("lsptopc: LSPs out of bounds; f(%d) = %f at frame %d\n",
	     i, f[i], frame);
  }
  if (lspflag)
    printf("lsptopc: nonmonotonic LSPs at frame %d\n", frame);

  /* *initialization 						 */

  pi = 3.1415926535897931032;
  noh = no / 2;
  for (j = 0; j < no; j++)
    freq[j] = f[j];
  for (i = 0; i < noh + 1; i++)
  {
    a[i] = 0.;
    a1[i] = 0.;
    a2[i] = 0.;
    b[i] = 0.;
    b1[i] = 0.;
    b2[i] = 0.;
  }

  /* *lsp filter parameters 					 */

  for (i = 0; i < noh; i++)
  {
    p[i] = -2. * cos(2. * pi * freq[2 * i]);
    q[i] = -2. * cos(2. * pi * freq[2 * i + 1]);
  }

  /* *impulse response of analysis filter 			 */

  xf = 0.0;
  for (k = 0; k < no + 1; k++)
  {
    xx = 0.0;
    if (k == 0)
      xx = 1.0;
    a[0] = xx + xf;
    b[0] = xx - xf;
    xf = xx;
    for (i = 0; i < noh; i++)
    {
      a[i + 1] = a[i] + p[i] * a1[i] + a2[i];
      b[i + 1] = b[i] + q[i] * b1[i] + b2[i];
      a2[i] = a1[i];
      a1[i] = a[i];
      b2[i] = b1[i];
      b1[i] = b[i];
    }
    if (k != 0)
      pc[k - 1] = -.5 * (a[noh] + b[noh]);
  }

  /* *convert to CELP's predictor coefficient array configuration */

  for (i = no - 1; i >= 0; i--)
    pc[i + 1] = -pc[i];
  pc[0] = 1.0;
}