1. A transmission system comprising a transmitter for transmitting an input signal via a transmission channel, and a receiver for receiving the transmitted input signal via the transmission channel; the transmitter comprising an encoder with an excitation sequence generator for generating a plurality of excitation sequences, selection means for selecting an excitation sequence resulting in a minimum error between a synthetic signal derived from said excitation sequence and a target signal derived from the input signal, the transmitter being arranged for transmitting a signal representing an optimal excitation sequence to the receiver; and the receiver comprising a decoder with an excitation sequence generator for deriving the selected excitation sequence from the signal representing the selected excitation sequence, and a synthesis filter for deriving a synthetic signal from the excitation sequence; wherein the encoder comprises a reduced complexity synthesis filter, which is reduced in order relative to the synthesis filter of the receiver, for deriving from the plurality of excitation sequences a plurality of synthetic signals, and the selection means are arranged for selecting an excitation sequence resulting in a minimum error between the corresponding synthetic signal and target signal.