transferFunction:: Int -> Number.Ratio.T (MathObj.Polynomial.T Double)
transferFunction n = const 1 % polynome where
  polynome = const alpha * p1^r * foldl (*) (const 1) (map p2 [1..l])
  p1 = fromCoeffs [alpha, 1]
  p2 n' = fromCoeffs [alpha^^2, 2 * alpha * sin(thetta n'), 1]
  thetta n' = (2 * fromIntegral n' - 1) / (2 * fromIntegral n) * pi
  alpha = fromdB attPass ** (- fromIntegral n)
  (l,r) = divMod n 2