A Low Latency Packet Loss Concealment Method for MIDI Signals

A Networked Music Performance (NMP) is a real-time interaction over a computer network which allows musicians in different places to perform as if they were in the same room. A crucial requirement of NMP is to have low latency, in order to make all musicians perceive that they are playing simultaneously while maintaining a stable tempo. In order to ensure a good NMP experience it is also necessary to ensure low packet loss rates due network congestion or excessive transmission delays. In the case of raw or codec-based audio streaming, the loss of packets causes the generation of sounds artifacts during the playback. Conversely, in the case of MIDI signals, since MIDI events encode the musician's actions and not the system status, packet losses could make the reproduced audio signal prolongedly different from the original one. For this reason it is essential to correct errors caused by the loss of one or more packets, so that the correct system status can be restored as soon as possible. In this thesis, we propose a packet loss concealment method that consists in sending information about the exact status of the system in addition to MIDI events, so that errors can be corrected in case of packet loss by restoring the system status. The proposed method and protocol have been implemented in a client-server prototype, where clients represent musicians and the server manages the playback of clients' messages and their corrections. Several tests carried out on this prototype show that, with a small transmission overhead, significant improvements in the perceived audio quality can be achieved.