in the g729a recommendation, the excitation is modelled using an
"algebraic codebook". what is meant by an "algebraic" codebook ??
also, the postfiltering stage of the decoder uses a tilt compensation
filter to compenstate for the spectral tilt of the short-term
postfilter. but why does the short-term filter introduce a spectral
tilt, when it is only supposed to emphasize the formant frequencies ??