Hierarchical audio encoder for network traffic adaptation
Leann M. Christianson, Kevin A. Brown · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1999
In this paper, we describe modifications to the rate multicast audio tool to allow audio stream to be hierarchically encoded. This allows the rate of audio data transmission to be selected by the receiver. This is particularly useful in multicast sessions where many users participate with diverse connectivity. The hierarchical encoder also allows dynamic adjustment of the received data rate to network conditions. The algorithm is based upon a simple pulse code modulation scheme. Speech is sampled at 8,000 samples per second with 16 bits per sample. The bits are then divided into groups based on their overall relative importance to the sample. A base group is defined which provides a reasonable approximation to the sample, but which discards most details. Each successive group adds more detail. The groups, which together represent different resolutions, are sent as separate data streams. The receiver subscribes to a set of data streams such that the total data rate can feasibly be delivered by the network. Bandwidth usage and signal resolution are easily adapted by adding or dropping groups. Performance was evaluated based on continuity and intelligibility of the speech segments as well as bandwidth usage and loss.