Before proceeding it is possible to anticipate a general feature of the Lanczos response function by recalling a property of the Gibbs oscillation. Even as number of terms in the Fourier series representation of a step function becomes very large, its amplitude has a lower bound of 9% .
The Lanczos filter smooths the discontinuity (as in Fig1) with the consequence that the above property is again present except that the amplitude of the Gibbs oscillation is significantly reduced.