lsp34.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.
%
% ******************************************************************
% LSP34
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 6-13-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Independent nonuniform scalar quantization of line spectral pairs
%
% DESIGN NOTES
%
% Independent (nondifferential) scalar LSP quantization.  Determine
% LSP quantization by refined sequential quantization.  Because the
% quantization tables overlap, sequential quantization can produce a
% nonmonotonic LSP vector.  For nonmonotinic LSPs, the quantization
% is refined by adjusting the quantization for minimum error by
% selecting 1 of the following 2 cases:
%
%   1. Quantize current LSP to next higher level
%   2. Quantize previous LSP to the next lower level
%
% VARIABLES
%
% INPUTS
%   freq     -      Input LSPs, unquantized
%   bits     -      Bit allocation
%   no       -      Order (predictor order)
%
% OUTPUTS
%   freq     -      Quantized LSPs
%   findex   -      Quantized LSP table indicies
%
% INTERNALS
%   i        -      Counter
%   low      -      Minimum quantization error
%   levels   -      Quantization levels allocated to current LSP
%   dist     -      Quantization error
%   errorup  -      Quantization error w.r.t. next higher quantile
%   errordn  -      Quantization error w.r.t. next lower quantile
%   Q        -      LSP quantization table, reorganized into a column vector
%                   for : based index computation
%
% GLOBALS
%   lspQ      -     LSP quantization table
%
% CONSTANTS
%   FSCALE   -      Frequency scale factor (system sample rate)
%   MAXNO    -      Predictor order
%
% ******************************************************************

function [ freq, findex ] = lsp34( freq, no, bits )

% DECLARE GLOBAL CONSTANTS 
global MAXNO

% DECLARE GLOBAL VARIABLES (STATIC)
global lspQ

% DEFINE CONSTANTS
FSCALE = 8000.00;

% INIT RETURN VECTOR
findex = zeros( MAXNO, 1 );

% INIT LOCAL VARIABLES
freq = FSCALE * freq;
levels = ( 2 .^ bits ) - 1;

% QUANTIZE ALL LSP FREQUENCIES AND FORCE MONOTONICITY
for i = 1:no

    % QUANTIZE TO NEAREST OUTPUT LEVEL
    dist = abs( freq(i) - lspQ(i,1:levels(i)+1) );
    [ low, findex(i) ] = min( dist );

    % ADJUST QUANTIZATION IF NONMONOTONICALLY QUANTIZED AND
    % FIND ADJUSTMENT FOR MINIMUM QUANTIZATION ERROR
    if i > 1
        if lspQ( i,findex(i) ) <= lspQ( i-1,findex(i-1) )
            errorup = abs( freq(i)   - lspQ(i,min(findex(i)+1,levels(i) )) ) + ...
                      abs( freq(i-1) - lspQ(i-1, findex(i-1)) );
            errordn = abs( freq(i)   - lspQ(i,findex(i)) ) + ...
                      abs( freq(i-1) - lspQ(i-1,max(findex(i-1)-1,0)) );

            % ADJUST INDEX FOR MINIMUM ERROR (AND PRESERVE MONOTONICITY)
            if errorup < errordn
                findex(i) = min( findex(i)+1, levels(i) );
                while ( lspQ(i,findex(i)) < lspQ(i-1,findex(i-1)) )
                    findex(i) = min( findex(i)+1, levels(i) );
                end
            elseif i == 1
                findex(i-1) = max( findex(i-1)-1, 0 );
            elseif lspQ( i-1, max(findex(i-1)-1, 0) ) > lspQ( i-2, findex(i-2) )
                findex(i-1) = max( findex(i-1)-1, 0 );
            else
                findex(i) = min( findex(i)+1, levels(i) );
                while lspQ( i, findex(i) ) < lspQ( i-1, findex(i-1) )
                    findex(i) = min( findex(i)+1, levels(i) );
                end
            end
        end
    end
end

% CORRECT FINDEX VALUES TO MAINTAIN COMPATIBILITY WITH C IMPLEMENTATION
findex = findex - 1;

% QUANTIZE LSP FREQUENCIES USING INDICIES FOUND ABOVE
% RESHAPE TO EXPLOIT : BASED INDEXING FOR COLUMN VECTOR INSTEAD OF
% LOOP INDEXING IN A TWO-DIMENSIONAL ARRAY
Q = reshape( lspQ',160,1);
freq( 1:no ) = Q( ((0:no-1)'*16)+findex(1:no)+1 ) / FSCALE;