t1=[1:256]*2*pi/7;
t2=[1:256]*2*pi/8;
a1=1;
a2=.5;
% this gives a frequency that is not one of the FFT freqs
x=a1*cos(t1) + a2*cos(t2);
subplot(211);
plot(x);
title('X = cos([1:256]*2*pi/7) + 0.5*cos([1:256]*2*pi/8)')

sig=1;
x=x+sig*randn(size(x));

subplot(212);
plot(x);
title(['Y_n=X_n+W_n  sigma_W = ',num2str(sig)]);

% print -deps ts1