A dual-band excitation LSP codec for very low bit rate transmission

In multiband excitation (MBE) vocoders, the excitation spectrum is a series of voiced/unvoiced (v/uv) bands. This allows each speech segment to be partially voiced and partially unvoiced. It has been found that excitation in low frequency region is mostly voiced whereas in high frequency area, it is usually unvoiced. Although dividing the excitation spectrum into several v/uv bands (12 bands are commonly used) provides better output speech quality, its implementation for very low bit rate transmission is very difficult, if not impossible. In the paper, a modified version called a dual-band excitation LSP vocoder is proposed. The excitation spectrum, in this case, contains either one or two v/uv bands. Line spectral pairs (LSP) are used to represent the spectral envelope because of its effectiveness. Speech quality at a transmission rate of 2 kbps has been found to be clear and intelligible