%--------------------------------------------------------------------------
%      Spectr_G is a function developped by J.C. COMTE  comtejc@gmail.com
%                              CNC  UMR CNRS 5229.
%                          Last Release  March. 2007
%
%         This work is protected by the CeCILL-C Licence (see below).
%
%
%  z : represents the signal s(t).
%  Fs: is the sampling frequency.
%  W_DT: is the Window size.
%  W_dT: is the Overlap between two consecutive windows.
%  v: is a parameter allowing ('y' or 'Y') to display the signal
%  and its Spectrogram.
%
%  F_Mb:  Magnitude Time-Frequency Matrix (to calculate the power spectrum,
%  calculate the square of F_Mb).
%  F_Mlg: is the Log10 of F_Mb.
%  f: is the frequency vector.
%  t: is the time vector.
%
% This software is governed by the [CeCILL|CeCILL-B|CeCILL-C] license under French law and
% abiding by the rules of distribution of free software.  You can  use, 
% modify and/ or redistribute the software under the terms of the [CeCILL|CeCILL-B|CeCILL-C]
% license as circulated by CEA, CNRS and INRIA at the following URL
% "http://www.cecill.info". 
% 
% As a counterpart to the access to the source code and  rights to copy,
% modify and redistribute granted by the license, users are provided only
% with a limited warranty  and the software's author,  the holder of the
% economic rights,  and the successive licensors  have only  limited
% liability. 
% 
% In this respect, the user's attention is drawn to the risks associated
% with loading,  using,  modifying and/or developing or reproducing the
% software by the user in light of its specific status of free software,
% that may mean  that it is complicated to manipulate,  and  that  also
% therefore means  that it is reserved for developers  and  experienced
% professionals having in-depth computer knowledge. Users are therefore
% encouraged to load and test the software's suitability as regards their
% requirements in conditions enabling the security of their systems and/or 
% data to be ensured and,  more generally, to use and operate it in the 
% same conditions as regards security. 
% 
% The fact that you are presently reading this means that you have had
% knowledge of the [CeCILL|CeCILL-B|CeCILL-C] license and that you accept its terms.
%  
%--------------------------------------------------------------------------
function [t, f, F_Mb, F_Mlg]=Spectr_G(z,Fs,W_DT,W_dT,v)

[nl nc]=size(z);

if nl>nc
    z=z';
    n=nl; nl=nc; nc=n;
end;

N_dT=floor(W_dT*Fs);
N_DT=floor(W_DT*Fs);
N=floor(nc/(N_DT-N_dT));
stp=(N_DT-N_dT);

for i=0:N-1,   
    n=1+i*stp;
    M(i+1,:)=z(1,n:n+N_DT);
end;

[Ml Mc]=size(M)

h=mean(M,2)*ones(1,Mc);
M=M-h;


h=ones(Ml,1)*hamming(Mc)';
M=M.*h;


k=2^(2+round(log(Mc)/log(2)));
n=k/2;

f=(0:n-1)*(Fs/k);
t=((0:Ml-1)/Ml)*(nc/Fs);


F_M=fftshift(fft(M,k,2),2);
F_M=sqrt(F_M.*conj(F_M));

F_Mb=2*(F_M(:,n+1:2*n))/Mc;
F_Mb=F_Mb';
F_Mlg=20*log10(F_Mb);

if (v=='y')||(v=='Y')
figure;    
subplot(2,1,1);
plot([0:nc-1]/Fs,z);
subplot(2,1,2);
pcolor(t,f,F_Mlg);
shading interp;
lighting phong;
end;