Elimination of transients in LPC based vocoders

It is known that transient impulses will appear in LPC (linear predictive coding)-based speech coders and vocoders because the filter parameters are changed periodically while an input signal is applied. These impulses may be heard as clicks and may cause overflow in electronic circuits. It is shown that the transients may be eliminated by changing the state vector appropriately at the same time as the filter parameters are changed. Expressions are derived for calculating such a change, and the validity of the proposed approach is demonstrated by simulations of a pitch-excited vocoder. Complete elimination of transients is achieved. Different filter structures behave differently with regard to transients, but it is shown that there are pair of states in two filters that will cause the same transients when the transfer functions are identical but the structures differ.<>