A speech coder based on decomposition of characteristic waveforms

For low-rate speech coding it is advantageous to represent the speech signal as an evolving characteristic waveform (CW). The CW evolves slowly when the speech signal is clearly voiced and rapidly when the speech signal is clearly unvoiced. The voiced (periodic) and unvoiced (nonperiodic) components of the speech signal can be separated by a simple nonadaptive filter in the CW domain. Because of perceptual effects, a significant increase in coding efficiency is obtained by coding these two components separately. A 2.4 kb/s coder using these principles was developed. In an independent evaluation, the performance of the 2.4 kb/s waveform interpolation (WI) coder was found to be at least equivalent to the 4.8 kb/s FS1016 standard for all of the many tests.