% generate a signal and draw it in the time-frequency domain
samplefreq=100;
tstep=1/samplefreq;

t1=0:tstep:0.5;
t2=0.5+tstep:tstep:1.0;
t=[t1 t2];
x=[sin(4*2*pi*t1) sin(9*pi*2*t2)];
n=size(t,2);
plot(t,x);


winsize=32;     % Szerokosc okna
M=zeros(0);     % Nie chcemy problemow w Matlabie
window=zeros(0);

% Dla kazdego okna uruchom FFT
for i=1:n-winsize
    window=x(i:i+winsize-1);
    
    X=abs(fft(window));                     % Spektrum mojego okna
    M(i,1:winsize/2+1)=X(1:winsize/2+1);    % Spektrum dodajemy do mesha.
end

% Wykresl
f=samplefreq*(0:winsize/2)/winsize;
t=1000*t(1+winsize/2:n-winsize/2);
figure;
mesh(f,t,M);
title('time-frequency analysis');
xlabel('freqency [Hz]');
ylabel('time [ms]');

waitforbuttonpress;