The method of claim 1, wherein said calculating an excitation signal further comprises:storing an initial phase difference value A0, wherein said initial phase difference value A0 has the form x/P-k/P2 ; wherein k is a constant; and wherein a first iteration of said summing said phase offset value ??'I (x)* with said phase difference value AI-1 to produce a new phase offset value ??'I (x)* uses