A study of design compromises for speech coders in packet networks

We present an objective and subjective comparison of alternative methods for improving the robustness of speech coders in packet networks. The two approaches are considered: 1) adding redundancy in the packets to improve the robustness of a baseline encoder; 2) reducing (or eliminating) inter-frame dependencies at the encoder. It is shown that both approaches have to trade bit rate and/or delay for quality over lossy channels. Formal subjective tests clearly show that, using relatively simple forward error correction methods, standard coders such as ITU-T recommendation G.729 can be made significantly more robust than "frame-independent" coders, at a lower or similar bit rate.