Speech processing system

An audio transmission system is provided which is operable to receive sets of signals representative of a speech signal generated by a speech source 7. The system includes a statistical analysis unit 21 which is operable to determine parameters representative of each of the sets of signal values, and an encoder 71 to encode these parameter values and then to transmit these parameter values to a receiver circuit 75. At the receiver, the encoded parameters are decoded at 76 to recover the parameter values. The recovered parameter values may then be used to resynthesise the speech using a speech synthesiser 79 or they may be used by a speech recognition system 77 to generate a recognition result. The statistical analysis unit 21 applies a set of received audio signal values to a stored predetermined function to provide a probability density for parameters of a predetermined audio model, parameters best representing the set then being derived. A measure of the quality of the audio signal may be determined so that an appropriate coding and/or decoding method can be employed.