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

/* Copyright 2001,2002,2003 NAH6 
 * All Rights Reserved 
 * 
 * Parts Copyright DoD, Parts Copyright Starium 
 * 
 */ 
          /*LINTLIBRARY*/ 
          /*PROTOLIB1*/ 
 
#include  
#include "main.h" 
#include "mexcite.h" 
 
/************************************************************************** 
* 
* ROUTINE 
*		ModifiedExcitation 
* 
* FUNCTION 
*		Modify the stochastic code book excitation gain 
* 
* SYNOPSIS 
*		ModifiedExcitation(LPC_res, Adapt_res, scale) 
* 
*   formal  
* 
*                       data    I/O 
*       name            type    type    function 
*       ------------------------------------------------------------------- 
*	LPC_res		float	 i	LPC residual 
*	Adapt_res	float	 i	Adaptive analysis residual 
*	scale		float	 o	Stochastice codebook gain scale 
* 
*========================================================================== 
*	 
* DESCRIPTION 
* 
*	Depending on the current system state, the stochastic code book 
*	excitation is reduced to a level that is low enough to produce 
*	positive perceptual effects, yet is high enough so as not to upset 
*	the dynamics of the system.  The main effect of the method is that 
*	during sustained voiced sounds, the excitation level is attenuated. 
*	In unvoiced and transition regions the level is amplified to a 
*	level slightly more than that of standard CELP. 
* 
*	The relative adaptive code book excitation component is 
*	increased in voiced regions by decreasing the stochastic code book 
*	excitation component.  The amount of decrease in the stochastic 
*	component depends on the efficiency of the adaptive component. 
*	More reconstruction burden is placed on the adaptive component as 
*	its efficiency increases.  The efficiency is measured by the 
*	closeness (in the squareroot crosscorrelation sense) of the residual 
*	signals before and after pitch prediction.  When the efficiency is  
*       high (e.g., > 0.9), the stochastic component is amplified slightly 
*	(e.g., one quantizer level). 
* 
*	The procedure for modifying the stochastic gain outside the 
*	search loop is: 
*	1)  Measure the efficiency of the adaptive component (ccor) 
*	2)  Search the stochastic code book for the optimum codeword 
*	3)  Modify the stochastic code book gain 
* 
*	This method is compatible with Federal Standard 1016. 
* 
*	This code represents the modified excitation work done by R556 which 
*	was inspired by the constrained excitation work done by Yair Shoham.  
* 
* 
*========================================================================== 
* 
* CALLED BY 
* 
*	Analysis 
* 
*========================================================================== 
* 
* REFERENCES 
* 
*	Shoham, Yair, "Constrained-Stochastic Excitation Coding of Speech 
*	at 4.8 kbps," in Advances in Speech Coding, ed. B. Atal, V. 
*	Cuperman, and A. Gersho, submitted to Kluwer Academic Publishers. 
* 
*	Shoham, Yair, "Constrained-Stochastic Excitation Coding of Speech,"  
*	Abstracts of the IEEE Workshop on Speech Coding for 
*	Telecommunications, 1989, p. 65. 
* 
***************************************************************************/ 
void ModifiedExcitation( 
float	LPC_res[RES_LEN], 
float	Adapt_res[RES_LEN], 
float	*scale) 
{ 
float	ccor, e1; 
int	i; 
 
/*  Calculate the Euclidean norm of the LPC residual */ 
	e1 = .000001; 
	for(i=0; i 0.9) 
	    *scale *= 1.4; 
 
 
}