lsptopc.m

实现fs1016w的CELP的低速率语音编解码功能的基于vc开发环境的原代码。

% 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.
%
% ******************************************************************
% LSPTOPC
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 6-15-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Convert lsp frequencies to predictor coefficients
%
% DESIGN NOTES
%
% LSPTOPC converts line spectral frequencies to LPC predictor
% coefficients.
%
% The analysis filter may be reconstructed:
%
%   A(z) = 1/2 [ P(z) + Q(z) ]
%
% LPC predictor coefficient convention is:
%          p+1     -(i-1)
%   A(z) = SUM a  z         where a  = +1.0
%          i=1  i                  1
%
% VARIABLES
%
% INPUTS
%   f          -     LSP frequencies
%   no         -     LPC filter order
%
% OUTPUTS
%   pc         -     LPC predictor coefficients
%
% INTERNALS
%   xx         -     Analysis filter excitation
%   xf         -     Analysis filter excitation
%   p          -     LSP filter polynomial
%   q          -     LSP filter polynomial
%   a          -     LSP filter output
%   b          -     LSP filter output
%   a1,a2      -     LSP filter memory
%   b1,b2      -     LSP filter memory
%   i,k        -     Loop counters
%   noh        -     no/2
%   freq       -     Local copy of LSP frequencies
%
% GLOBALS
%   FrameCnt   -     Current frame number
%
% ******************************************************************

function pc = lsptopc( f, no )

% DECLARE GLOBAL VARIABLES
global FrameCnt

% TEST FOR ILL-CONDITIONED INPUT LSPs
if ( any(f<=0.00) | any(f>=0.5) )
    fprintf( 'lpstopc: LSPs out of bounds at frame %d\n', FrameCnt );
end
if any( f(2:no) <= f(1:no-1) )
    fprintf( 'lpstopc: nonmonotonic LSPs at frame %d\n', FrameCnt );
end

% INITIALIZE LOCAL VARIABLES
noh = no / 2;
freq = f;
a = zeros( noh+1, 1 );
a1 = a;
a2 = a;
b = a;
b1 = a;
b2 = a;
pc = zeros( no, 1 );

% INITIALIZE LSP FILTER PARAMETERS
p = -2 * cos( 2*pi*freq((1:2:no-1)') );
q = -2 * cos( 2*pi*freq((2:2:no)') );

% COMPUTE IMPULSE RESPONSE OF ANALYSIS FILTER
xf = 0.00;
for k = 1:no+1
    xx = 0.00;
    if k == 1
        xx = 1.00;
    end
    a(1) = xx + xf;
    b(1) = xx - xf;
    xf = xx;
    for i = 1:noh
        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);
    end
    if k ~= 1
        pc(k-1) = -0.5 * ( a(noh+1) + b(noh+1) );
    end
end

% CONVERT TO PREDICTOR COEFFICIENT ARRAY CONFIGURATION
pc(2:no+1) = -pc(1:no);
pc(1) = 1.0;