% view filter frequency response

[b,a]= butter(6,2000/(fsi/2),'low');
h= impz(b,a,N); % stem(h)

H=(abs(fft(h))); 
fscale= fsi/N*(1:N/2); 
figure(4), plot(fscale,1/200*Y(1:N/2)), xlabel('f [Hz]') %plot signal
hold on
plot(fscale,H(1:N/2),'r') % plot filter frequency response
hold off
legend('signal','LP filter')