Subjective evaluation of packet loss recovery techniques for voice over IP

We conducted a subjective evaluation experiment for VoIP speech under severe packet loss condition. The target codec was G.729, and four packet loss concealment methods were tested: parameter redundancy, SVM-based parameter redundancy, N-gram-based parameter estimation and interleaving. We first evaluated the effect of the interleaving block length on the subjective delay and speech quality. As a result, we found that the interleaving improved the subjective speech quality, but longer block length did not improve the quality. Next, we investigated the effect of PLC methods on the subjective latency and quality, and we found interleaving and simple PLC method gave the best result. N-gram-based PLC method made the quality worse.