Design and implementation of a parametric speech coder

Speech coders based on linear predictive coding are good and accurate in modeling speech utterances. They not only model speech utterance in an accurate manner but have the following properties: i) they provide a good estimate of the vocal tract spectral envelope; ii) they are analytically tractable; iii) they can be implemented in either software or hardware; iv) they use less data storage than many other approaches of speech coders. In this paper, a hybrid speech coder based on code excited linear predictive coding (CELPC) and voice excited linear predictive coding (VELPC) is presented. CELPC is one of the main techniques for producing high quality speech at around 4.8 kbps. However, the computation requirement for the original CELPC was too demanding and not suitable for practical use. Therefore, a hybrid approach to produce speech signals with high quality and with a bit rate of 3.478 kbps has been proposed. This method splits the speech signal into two portions, the base-band signal and the high-band signal in the frequency domain. The base-band and the high-band signal are then coded using the CELPC and VELPC techniques, respectively.