The audio outputs 29 of each of a plurality of telecommunications terminals in a packet switched system are synchronized by having each terminal transmit a stream of packets whose rate, and therefore duration is determined according to a clock generator 25, and is thus indicative of the rate at which the terminal is generating its audio output. The signals from each terminal are transmitted to a common server. For each terminal, the server uses a master dock to compare the duration of the packet stream with an expected duration, and calculates an offset value which is returned to the respective terminal. Each terminal stores the offset value it receives (20) and uses it to adjust the output of its clock generator 25 so that its operations can be synchronized to the server. This allows all the terminals' digital-to-analog conversion processes to be synchronized such that all their analog outputs are coordinated, allowing co-located acoustic outputs to be synchronous. A second embodiment maintains synchronization by maintaining the volume of the data buffer 23 serving the audio output 29 within predetermined limits.