We propose in this paper a new point of view which unies two w ell known lter families for approximating ideal fractional delay lters: Lagrange Interpolator Filters (LIF) and Thiran Allpass Filters. We a c hieve this unication by approximating the ideal Fourier transform of the fractional delay according to two dierent Pad e approximations: series expansions and continued fraction expansions, and by proving that both approximations correspond exactly either to the LIF family or to the allpass

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... lay lters family. This leads to an ecient modular implementation of LIFs.