Low bit rate vocoder algorithm for videoconferencing and Internet phone

This paper analyzes the dynamic sparse algebraic codebook used to model a residual signal and proposes a new algebraic codebook structure as well as a searching process with improved performance. This paper makes it possible to select various pulse amplitudes differently from the conventional method. In addition, two pulses can be selected on the same track and LP delay is minimized at the transient period. For speech quality on the telephone line, a 5.6 kbps speech coder using the proposed algorithm was equivalent to the 6.3 kbps MP-MLQ in the subjective speech quality test. However, speech degradation was caused a little compared with the MP-MLQ where MNRU Q=15 dB.