Low bit rate coding using an interpolated zinc excitation model

Prototype excitation vocoding has been of particular interest, particularly at bit rates below 4 kbits/sec where conventional analysis by synthesis (AbS) LPC based coders fail to deliver the speech quality required in a number of new voice communication applications and services. The present authors propose a new time domain, interpolated zinc function prototype excitation technique (IZFPE) for communications quality speech at about 2.0 kb/s. In this method a prototype pitch segment is selected every 20 ms. Each prototype segment is then modelled by a zinc orthogonal function which is derived by employing a closed loop AbS procedure (ZFE-AbS). Successive prototype zinc excitations are then interpolated such that the characteristics of the resulting excitation signal evolve slowly with time