www.pudn.com > CryptoPhone-src-031122.zip > lsftopc.c

/* Copyright 2001,2002,2003 NAH6 
 * All Rights Reserved 
 * 
 * Parts Copyright DoD, Parts Copyright Starium 
 * 
 */ 
          /*LINTLIBRARY*/ 
          /*PROTOLIB1*/ 
 
#include  
#include  
#include "main.h" 
#include "lsftopc.h" 
 
/************************************************************************* 
* 
* NAME 
*	LSFtoPC  
* 
* FUNCTION 
* 
*	convert line spectral frequencies to predictor coefficients 
* 
* SYNOPSIS 
* 
*	LSFtoPC(f, pc, frame_num) 
*  
*   formal 
*			data	I/O 
*	name		type	type	function 
*	------------------------------------------------------------------- 
*	f		real	i	lsp frequencies 
*	pc		real	o	LPC predictor coefficients 
*	frame_num	int	i	Frame number 
* 
* 
*************************************************************************** 
* 
* DESCRIPTION 
* 
*	LSFtoPC converts line spectral frequencies to 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 
* 
***************************************************************************/ 
void LSFtoPC( 
float	lsf[ORDER], 
float	pc[ORDER+1], 
int	frame_num) 
{ 
int 	i, j; 
float	pi, xf, xx; 
int	half_order; 
float	a[ORDER/2 +1], a1[ORDER/2 +1], a2[ORDER/2 +1]; 
float	b[ORDER/2 +1], b1[ORDER/2 +1], b2[ORDER/2 +1]; 
float	p[ORDER/2], q[ORDER/2]; 
float	freq[ORDER]; 
 
 
/*  Check input for ill-conditioned cases */ 
	if( (lsf[0] <= 0.0) || (lsf[0] >= 0.5) )	{ 
	  printf("LSFtoPC: LSFs out of bounds; lsf[0] = %1.4f at frame %d\n", 
		lsf[0], frame_num); 
	} 
 
	for(i=1; i= 0.5) ) 
	    printf("LSFtoPC: LSFs out of bounds; lsf[%d] = %1.4f at frame %d\n", 
		i, lsf[i], frame_num); 
	} 
 
/*  Initialization */ 
/*	pi = 4*atan(1.0);*/ 
  	pi = 3.1415926535897931032; 
 
	for(i=0;i 0) 
	    pc[i-1] = -0.5 * (a[half_order] + b[half_order]); 
 
	}	 
 
/*  Convert to CELPs PC array configuration */ 
	for(i=9;i>=0;i--)	 
	  pc[i+1] = -pc[i]; 
	pc[0] = 1.0; 
 
 
}