Minimal multiplier realisation of bilinear-LDI digital allpass networks

The authors outline a procedure for the bilinear-LDI digital realisation of arbitrary-order stable analogue allpass transfer functions. The salient features of the resulting digital networks are: (i) they are structurally allpass, i.e. their transfer functions are allpass independently of the specific choice of their multiplier coefficient values; (ii) they are minimal in the number of digital multipliers required; and (iii) they require only one unit delay more than the minimum number possible. A comparison shows that, in terms of number of operations, these allpass networks are superior to the corresponding direct-form, direct-cascade-form and wave-digital realisations.<>