function y = mg_NOI_filter(b, a, x)
ma = length(a);
mb = length(b);
n = length(x);
y = zeros(1, n);

for i = 1:n
  z = 0;
  for j = 1:mb
    if ((i-j+1) < 1)
      z += 0;
    else
      z += x(i-j+1)*b(j);
    endif;
  endfor;

  for k = 1:ma
    if ((i-k+1) < 1)
      z -= 0;
    else
      z -= x(i-k+1)*a(k);
    endif;
  endfor;

  y(i) = z;
endfor;
endfunction