A 6.4 kbit/s extension to the G.729 speech coder

This paper proposes a 6.4-kbit/s extension to the G.729 speech coder. Each G.729 module was investigated to determine which bits could be removed without hurting the speech quality, then a 6.4-kbit/s coder was designed. This coder has an 11-bit algebraic codebook that uses two or three pulses. We also propose a conditional orthogonalized search for the fixed codebook to improve the speech quality. The conditional orthogonalized search chooses one of two search methods (orthogonalized or non-orthogonalized) based on the optimum pitch gain. Subjective tests have indicated that the quality of the proposed coder is equivalent to that of the 6.3-kbit/s G.723.1 coder.