In a digital speech encoding system wherein the transmitter substitutes for the original speech signal to be encoded (1) certain parameters supplied by an analysis circuit defining, within successive time frames, the characteristics of a synthesis filter modeling the vocal tract and located at a receiver connected to the transmitter via a low-bit-rate data link, and (2) a multipulse excitation signal intended for said synthesis filter and supplied by a pulse generating circuit which determines the pulse position and amplitudes by successive approximation minimizing the mean squared error between the original speech signal and the synthetic speech signal obtained from the filter, the pulse generating circuit adds to the amplitude of each of the pulses, at the end of the approximation routine, a corrective term that is a function of the value of the partial derivative of the mean squared error taken relative to the amplitude of the pulse under consideration, taken as an independent variable.