pctorc.m

FS1016源代码

% MATLAB SIMULATION OF NSA FS-1016 CELP v3.2
% COPYRIGHT (C) 1995-99 ANDREAS SPANIAS AND TED PAINTER
%
% This Copyright applies only to this particular MATLAB implementation
% of the FS-1016 CELP coder.  The MATLAB software is intended only for educational
% purposes.  No other use is intended or authorized.  This is not a public
% domain program and distribution to individuals or networks is strictly
% prohibited.  Be aware that use of the standard in any form is goverened
% by rules of the US DoD.  Therefore patents and royalties may apply to
% authors, companies, or committees associated with this standard, FS-1016.  For
% questions regarding the MATLAB implementation please contact Andreas
% Spanias at  [phone].  For questions on rules,
% royalties, or patents associated with the standard, please contact the DoD.
%
% ALL DERIVATIVE WORKS MUST INCLUDE THIS COPYRIGHT NOTICE.
%
% ******************************************************************
% PCTORC
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 6-9-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Convert from lp-polynomial (direct form) to reflection coefficients
%
% DESIGN NOTES
%
% This routine uses the Levinson recursion to compute reflection
% coefficients from the LPC coefficients.  The first LPC
% coefficient is assumed to be 1, and although it is passed
% to the routine, it is not used in the calculations.
%
% LPC predictor coefficient convention is:
%
%          p+1       -(i-1)
%   A(z) = SUM   a  z          where a  = +1.0
%          i=1    i                   1
%
% The sign convention used defines the first reflection coefficient
% as the normalized first autocorrelation coefficient, which results
% in positive values of rc(1) for voiced speech.
%
% VARIABLES
%
% INPUTS
%   lpc      -      Direct form (A(Z)) predictor coefficients (n+1)
%   n        -      Predictor order
%
% OUTPUTS
%   rc       -      Reflection coefficients (voiced -> +rc(1) )
%
% INTERNALS
%   a        -      Copy of input predictor polynomial
%   t        -      Temporary for intermediate recursion results
%   i        -      Index of recursion
%
% GLOBALS
%   MAXNO    -      Predictor order ( A(Z) )
%
% ******************************************************************

function rc = pctorc( lpc, n )

% DECLARE GLOBAL CONSTANTS
global MAXNO

% ALLOCATE RETURN VECTOR AND INIT LOCAL COPY OF PREDICTOR POLYNOMIAL 
rc = zeros( MAXNO, 1 );
a = lpc;

% DO LEVINSON RECURSION
for i = n:-1:2
    rc(i) = -a( i+1 );
    t( i:-1:2 ) = ( a( i:-1:2 ) + ( rc(i) .* a(2:i) ) ) / ...
                  ( 1.0 - ( rc(i) * rc(i) ) );
    a( 2:i ) = t( 2:i );
end
rc(1) = -a(2);