SPEECH CODING

A variable bit-rate speech coding method determines for each subframe a quantised vector d(i) comprising a variable number of pulses. An excitation vector c(i) for exciting LTP and LPC synthesis filters is derived by filtering the quantised vector d(i), and a gain value gc is determined for scaling the pulse amplitude excitation vector c(i) such that the scaled excitation vector represents the weighted residual signal {tilde over (s)} remaining in the subframe speech signal after removal of redundant information by LPC and LTP analysis. A predicted gain value ĝc is determined from previously processed subframes, and as a function of the energy Ec contained in the excitation vector c(i) when the amplitude of that vector is scaled in dependence upon the number of pulses m in the quantised vector d(i). A quantised gain correction factor {circumflex over (&ggr;)}gc is then determined using the gain value gc and the predicted gain value ĝc.