polefilt.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.
%
% ******************************************************************
% POLEFILT
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 6-22-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Direct form IIR, all-pole filter
%
% DESIGN NOTES
%
% Recursive all-pole in-place time-domain filter.
% The transfer function 1/A(z) is implemented
% in a direct form realisation.
%
%               N       -i
%   H(z) = 1 / SUM a(i)z         with a(0) = +1.0
%              i=0
%
% NOTE:  a(0) is not used for the actual computing,
%        as can easily be seen in the following flow graph.
%
%   x(t) ->---+------->--------(z0)-----> y(t)
%             |                  |
%             +-------< -a1 ----z1
%             |                  |
%             +-------< -a2 ----z2
%             |                  |
%             :                  :
%             |                  |
%             +-------< -aN ----zN
%
% VARIABLES
%
% INPUTS
%   a          -     N+1 tap weights
%   n          -     Filter order, N
%   z          -     Filter memory
%   xy         -     Input sequence
%   len        -     Input sequence length
%
% OUTPUTS
%   z          -     Filter memory
%   xy         -     Output sequence
%
% INTERNALS
%   t          -     Sequence index value
%   ar         -     Weighted sum accumulator
%
% ******************************************************************

function [ z, xy ] = polefilt( a, n, z, xy, len )

if a(1) ~= 1.0
    fprintf( 'polefilt: bad coefficients\n');
end

for t = 1:len
    z(1) = xy(t) - sum( z(2:n+1) .* a(2:n+1) );
    z(2:n+1) = z(1:n);
    xy(t) = z(1);
end