Smart Internet CRC Control of Multiple Audio Streams

A growing area of technical importance is that of distributed virtual environments for work and play.

The problem

For the audio component of such environments to be useful, great emphasis must be placed on the delivery of high quality audio scenes in which participants may change their relative positions. By maintaining synchronisation, an end-user is ensured a more stable audio environment, which will assist in maximising the usability of the application especially when the application characteristics are highly dynamic.

The Smart Internet CRC was interested in designing a multimedia application focussed on an immersive virtual environment. In this project, it was apparent that an integral part of constructing such an environment was the realism of the audio component. To further add complexity, there was a desire to enable a large number of users to communicate with and over-hear other users in the environment, such as would occur in a cafe environment in the real world. The Teletraffic Research Centre's contribution to this project was the design of synchronisation algorithm to assist in the delivery of high quality interactive audio to the end-users.

The solution

The delivered solution was in the form of an efficient algorithm that can achieve and maintain relative synchronisation between audio streams in a real time audio mixing environment.

The algorithm does not attempt to maintain absolute synchronisation between audio streams, as this would require the use of global timing. Rather, the algorithm attempts to maintain consistency within the mixing process such that the alignment of audio samples from each stream remains as constant as possible given the random elements of network delay.

The algorithm is able to adapt quickly to gross changes in the underlying delays of each stream, as might result from network link failures. At the same time, the proposed algorithm is robust to short term variations in delay resulting from audio stream packets being queued at routers.