Variable rate multi-mode excitation coding of speech at 2.4 kbps

A variable rate speech coder utilizing speech classification is presented as a cost effective solution to applications where low bit rate, good quality, and less complexity are the main objectives. The coder operates at an average rate of 2.4 kbps and the speech quality is close to that produced by the ITU G.723.1 codec. It has been implemented with less than 10 MIPS, 2.5 K RAM, 3.3 K DROM, and 6 K PROM on a 16-bit fixed-point general purpose DSP. The framework of the coder is based on multi-pulse and code-excited coding schemes. The rate variation and coding efficiency are manifested in a multimode excitation modeling depending on the nature of the input speech.