Error Propagation After Concealing a Lost Speech Frame
Christian Hoene, Ian Marsh, Günter Schäfer, Adam Wolisz · 2006
Abstract — Depending on the content of speech frames, the quality impairment after their loss differs widely. In previous publications we described an off-line measurement procedure to determine the loss impairment – the importance – of single speech frames. We showed that knowing the importance of frames can enhance the transmission performance of VoIP telephones significantly if only important frames are transmitted. Here we study to what extend the importance can be calculated at real-time: The loss impairment is due to the imperfect packet loss concealment (PLC) and also due to error propagation (EP). EP originates from the desynchronisation of the decoder’s internal state and cannot be calculated at real-time. We developed a measurement method to determine the effect of the imperfect PLC and the temporal progression of the error propagation. The results show the trade-off between algorithmic delay and the accuracy of real-time importance calculation: A good frame classification needs to look ahead 20-40 ms in order to calculate the importance precisely. I.