Design of a VOCODER using instants of significant excitation

Vocoders are designed / used to reduce the number of bits required to represent the speech signal without significant degradation in the resultant speech quality. In most of the speech coding techniques, the system and the source parameters are coded separately. The system is generally coded using a codebook which demands only less number of bits. Coding of the source parameters requires significant computational complexity and memory to preserve the identity and naturalness of the speaker. In this work, a LPC vocoder is designed which uses the instants of significant excitation estimated from the speech signal to code the source information. Traditional pitch excited LPC vocoders produce intelligible speech at a bit rate of 2400 bps, but they are often synthetic. Hence source is coded by identifying the locations of instants of significant excitation and the corresponding strength at those instants. Thus the bit rate requirement is reduced significantly in the order of 1.6 Kbps which is promising. Also, the performance analysis shows that the resultant synthesized speech is intelligible and quite natural preserving the identity of the speaker.