An audio data processing system is a client-server system including an audio data communication device and an audio data processing device which are linked together via a communication network. The audio data communication device includes an acoustic generator, a control device, a transmitter and a receiver in connection with first and second storage areas. The transmitter sequentially transmits a time series of unprocessed data DA[n] stored in the first storage area, while the receiver sequentially receives a time series of processing-completed data DB[n] from the acoustic data processing device so that processing-completed data are stored in the second storage area and sequentially reproduced. When specific processing-completed data is not stored in the second storage area, the control device designates and reproduces specific unprocessed data, which is unprocessed acoustic data corresponding to specific processing-completed data. Alternatively, the control device designates and reproduces cross-faded acoustic data, combining unprocessed data and processing-completed data.