Interpolated Allpass Fractional-Delay Filters Using Root Displacement

Fractional-delay filter is the general name given to filters modelling non-integer delays. Such filters have a flat phase delay for a wide frequency band, with the value of the phase delay approximating the fractional delay. A maximally-flat delay IIR fractional-delay filter can be obtained by the Thiran approximation. A simple and efficient method for obtaining filters modelling intermediate fractional delays from two Thiran fractional-delay filters is proposed. The proposed method allows continuously modifying the fractional delay. Computational complexity of the proposed method is discussed. A practical application of the method in model-based sound synthesis is given as an example