Comment on "Roundoff Noise and Attenation Sensitivity Digital Filters with Fixed-Point Arithmetic

The relation between roundoff noise and attenuation sensitivity in digital filters with fixed-point arithmetic given in a letter by Fettweis (A Fettseis, IEEE Trans. Citcuit Theory, Vol. CT-20, pp. 174-175, March 1973) is found to be overly simplified. Some examples where the preceding relation does not hold are given along with a tentative explanation.