function myfft(x,fs)
l = length(x);
n = floor(l*6/fs);

length(1:floor(l/2));
F = abs(fft(x));
plot(linspace(0,fs/2,floor(l/2)),F(1:floor(l/2)));
title('FFT analysis');
xlabel('Frequency (Hz)');
ylabel('Power');
title('FFT analysis');
axis([0 6 0 10*mean(F(1:n))]);