Low-delay CELP and tree coders: comparison and performance improvements

A stochastic tree coder based on the (M,L) search algorithm suggested by V. Iyengar and P. Kabal (1988) and a low-day CELP (code-excited linear prediction) coder proposed by J.H. Chen (1989) are considered. The individual components (predictors, gain adaptation, excitation coding) of the two coders are analyzed. The performances of the two types of coders are compared. The two coders have comparable performance at 16 kb/s under clean channel conditions. Methods to improve the performance of the coders, particularly with a view to bringing the bit rate to below 16 kb/s, are studied. Suggestions for improving the performance include an improved high-order predictor (applicable to both coders), and training of the excitation dictionary as well as a better gain adaptation strategy for the tree coder