imdct.m

linear time－frequency toolbox

function [f]=imdct(c,g,Ls)
%IMDCT  Inverse MDCT
%   Usage:  f=imdct(c,g);
%           f=imdct(c,g,Ls);
%
%   Input parameters:
%         c     : M*N array of coefficients.
%         g     : Window function.
%         Ls    : Final length of function (optional)
%   Output parameters:
%         f     : Input data
%
%   IMDCT(c,g) computes an inverse MDCT with window g.
%   The number of channels is deduced from the size of the coefficient
%   array c.
%
%   g must be whole-point even.
%
%   IMDCT(f,g,Ls) does the same, but cuts or zero-extend the final
%   result to length Ls.
%
%   SEE ALSO:  MDCT, DGT, WILDUAL, WILORTH
%
%   REFERENCES:
%     H. Bölcskei and F. Hlawatsch. Oversampled Wilson-type cosine modulated
%     filter banks with linear phase. In Asilomar Conf. on Signals, Systems, and
%     Computers, pages 998-1002, nov 1996.
%     
%     H. S. Malvar. Signal Processing with Lapped Transforms. Artech House
%     Publishers, 1992.
%     
%     J. P. Princen and A. B. Bradley. Analysis/synthesis filter bank design based
%     on time domain aliasing cancellation. IEEE Transactions on Acoustics,
%     Speech, and Signal Processing, ASSP-34(5):1153-1161, 1986.
%     
%     J. P. Princen, A. W. Johnson, and A. B. Bradley. Subband/transform coding
%     using filter bank designs based on time domain aliasing cancellation.
%     Proceedings - ICASSP, IEEE International Conference on Acoustics, Speech and
%     Signal Processing, pages 2161-2164, 1987.

%   Author : Peter Soendergaard.

error(nargchk(2,3,nargin));

if size(g,2)>1
  if size(g,1)>1
    error('g must be a vector');
  else
    % g was a row vector.
    g=g(:);
  end;
end;

% If input is real, and window is real, output must be real as well.
inputwasreal = (isreal(g) && isreal(c));

Lwindow=size(g,1);
wasrow=0;

M=size(c,1);
N=size(c,2);
W=size(c,3);

L=M*N;

Lwindow=size(g,1);

% Length of window must be dividable by M.
if rem(Lwindow,M)~=0
  error('Length of window must be dividable by M.')
end;

% Call computational subroutine.
a=M;

c=comp_idwiltiii(reshape(c,M*N,W),a,M);

f=comp_igdgt(c,g,a,2*M,L,0,.5,0,0);

% Check if Ls was specified.
if nargin==3
  f=postpad(f,Ls);
else
  Ls=L;
end;


f=comp_sigreshape_post(f,Ls,wasrow,[0; W]);

% Clean signal if it is known to be real
if inputwasreal
  f=real(f);
end;