dcodtau.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.
%
% ******************************************************************
% DCODTAU
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 8-4-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Decodes all pitch tau values for a frame
%
% DESIGN NOTES
%
% Converts pitch delay bits from the bit stream to actual pitch delays,
% using table lookups and delay calculations.
%
% VARIABLES
%
% INPUTS
%   taubits    -     Number of bits allocated for odd frame tau quantization
%   taudelta   -     Number of bits allocated for even frame delta coding
%   bitsum1    -     Number of bits for odd subframes
%   bitsum2    -     Number of bits for even subframes
%   bitpointer -     Number of bits used
%   nn         -     Number of subframes
%   stream     -     Bit stream
%   pddecode   -     Pitch delay permutation table
%   pdtabi     -     Pitch delay table index
%
% OUTPUTS
%   taus       -     Vector of pitch delays
%   bitpointer -     Number of bits used
%
% INTERNALS
%   pointer    -     Current position in the bit stream
%   tptr       -     Tau decode table index
%   mnptr      -     Pitch delay table index lower limit
%   mxptr      -     Pitch delay table index upper limit
%   i          -     Loop index
%
% GLOBALS
%   plevel1    -     Number of full search pitch delays
%   plevel2    -     Number of delta search pitch delays
%   lptrDT     -     Delta decoding temporary
%   pdelay     -     Adaptive codebook pitch delays
%
% ******************************************************************

function [ taus, bitpointer ] = dcodtau( taubits, taudelta, bitsum1, ...
                                         bitsum2, bitpointer, nn, ...
                                         stream, pddecode, pdtabi )

% DECLARE GLOBAL VARIABLES
global plevel1 plevel2 lptrDT pdelay

% INIT RETURN VECTOR
taus = zeros( nn, 1 );

% ESTABLISH STARTING BIT STREAM POSITION
pointer = bitpointer;

% RUN DECODING FOR ALL SUBFRAMES
for i = 1:nn
    if rem( i,2 ) ~= 0

        % ODD SUBFRAME DELAY DECODE
        [ tptr, pointer ] = unpack( stream, taubits, pointer );
        taus(i) = pddecode( tptr+1 );
        pointer = pointer + bitsum1 - taubits;
    else

        % EVEN SUBFRAME DELTA DELAY DECODE
        [ tptr, pointer ] = unpack( stream, taudelta, pointer );
        pointer = pointer + bitsum2 - taudelta;
        mnptr = lptrDT - ( (plevel2/2) - 1 );
        mxptr = lptrDT + (plevel2/2);
        if mnptr < 0
            mnptr = 0;
        end
        if mxptr > ( plevel1-1 )
            mnptr = plevel1 - plevel2;
        end
        taus(i) = pdelay( tptr + mnptr + 1 );
    end
    lptrDT = pdtabi( tptr+1 );
end

% UPDATE BIT STREAM INDEX
bitpointer = bitpointer + taubits;