Apparatus and method for coding speech signals

An audio signal encoding device is provided including an input for receiving a sub-frame of an audio signal to be encoded, an adaptive codebook and a processing unit. The adaptive codebook stores at least one prior knowledge entry which includes a data element representative of characteristics of at least a portion of a previously generated audio signal sub-frame. The processing unit generates a set of parameters allowing for synthesization of the audio signal sub-frame received at the input on the basis of at least the sub-frame of the audio signal received at the input and the data element stored in the adaptive codebook. A corresponding decoding device for synthesizing an audio signal on the basis of a set of parameters is also provided.