An allpass transformed lattice filter with improved sensitivity properties

The sensitivity of a lattice filter pole location to perturbation of the PARCOR coefficients determines the number of bits of precision required for scalar quantization of those coefficients in LPC. It is demonstrated that the sensitivity characteristics can be altered without sacrificing the desirable properties of the lattice filter. Further, it is argued that for speech it is desirable to lower the sensitivity at low frequencies at the expense of higher frequencies, which can be accomplished by a simple one- pole allpass transformation. The resulting reduction in bit rate is comparable to that obtained by preemphasis.