Trajectory and surface modeling of LSF for low rate speech coding
In low rate speech coders, frame-based speech spectral parameters, represented by Line Spectral Frequencies (LSF), are typically encoded by vector quantization without exploiting explicitly the temporal correlation between frames. Recently, however, methods have been proposed that model the temporal trajectory of each LSF over a speech segment by a low-order polynomial function. In the present paper, the authors propose a method that exploits the joint spectro-temporal correlation across a speech segment. The LSF values are treated as points on a smooth surface obtained by fitting a low-order bivariate polynomial function of the variables, frame index and LSF index.