Design of a variable rate algorithm for the 8 kb/s CS-ACELP coder

In this paper, we propose an efficient variable rate algorithm for G.729. The variable rate algorithm consists of two main subjects, the rate determination algorithm and the design of sub rate coders. For the rate determination, we combine the energy-thresholding method, the phonetic segmentation method and the variable hangover period method. Through the analysis of noise features, a 1 kb/s sub rate coder is designed for coding the background noise signal. Also, we design a 4 kb/s sub rate coder for the unvoiced parts. Experiments show that the proposed variable rate conjugate structure-algebraic code excited linear prediction (CS-ACELP) coder produces the same speech quality as G.729, at the average bit rate of 4.4 kb/s