c_anablock.m

Sparse Signal Representation using Overlapping Frames (matlab toolbox)

function y=C_anablock(x,h1,h2)
% C_anablock  Analysis block in a FIR two channel filterbank 
%
% y=C_anablock(x,h1,h2);
% ----------------------------------------------
% Arguments:
%   x    - the signal, a column vector (or a matrix of column vectors)
%          each column is filtered independently of each other
%          [N,L]=size(x);   and we should have mod(N,2)==0
%   h1   - the FIR filter for the upper branch (low pass)
%   h2   - the FIR filter for the lower branch (high pass)
%   y    - the subbands, size(y)=[N/2,2*L], where odd columns correspond to
%          the upper branch, and even columns to the lower branch
% ----------------------------------------------
% Note that we assume circular expansion of the signal x

%----------------------------------------------------------------------
% Copyright (c) 1999.  Karl Skretting.  All rights reserved.
% Hogskolen in Stavanger (Stavanger University), Signal Processing Group
% Mail:  [e-mail]   Homepage:  http://www.ux.his.no/~karlsk/
% 
% HISTORY:
% Ver. 1.0  20.08.1999  KS: Function made
% Ver. 1.1  02.12.2002  KS: moved from ..\Frames to ..\FrameTools\
%----------------------------------------------------------------------

Mfile='C_anablock';
Circular=1;       % make circular expansion of signal (results)

if (nargin ~= 3)
   error([Mfile,': wrong number of arguments, see help.']);
end

[N,L]=size(x);
if (mod(N,2)) 
   error([Mfile,': length of signal(s) is not a factor of two, see help.']);
end
N1=length(h1);
N2=length(h2);
% make sure filters have odd length
if mod(N1-1,2); h1=[h1(:);0]; N1=N1+1; end;
if mod(N2-1,2); h2=[h2(:);0]; N2=N2+1; end;
N3=max([N1,N2]);
y=zeros((N+N3-1)/2,2*L);

for l=1:L
   % upper branch
   u=conv(x(:,l),h1);
   u=reshape(u,2,(N+N1-1)/2);  % N1 is odd and N is even
   y(1:((N+N1-1)/2),2*l-1)=u(2,:)';
   % lower branch
   u=conv(x(:,l),h2);
   u=reshape(u,2,(N+N2-1)/2);  % N2 is odd and N is even
   y(1:((N+N2-1)/2),2*l)=u(2,:)';
end

if Circular
   first=1:((N3-1)/2);
   middle=((N3+1)/2):(N/2);
   last=(N/2+1):((N+N3-1)/2);
   y=[y(first,:)+y(last,:);y(middle,:)];
end


return;