Time-warping and re-phasing in packet loss concealment

This paper proposes two techniques to improve packet loss concealment (PLC). In the first technique, time-warping is used to stretch or shrink the time axis of the signal received in the first good frame after frame loss to align it with the extrapolated signal used to conceal the bad frame. This aligning procedure avoids any destructive interference that might otherwise occur when the two signals are out of phase and overlap-added. The second technique may be applied to speech codecs with memory, particularly suited for backward-adaptive systems. In this technique, called “rephasing”, the internal states of the codec are phase-aligned with the signal in the first good frame. Both techniques are part of the ITU-T G.722 Appendix III packet loss concealment standard and provide significant quality improvement.