Pitch resynchronization while recovering from a late frame in a predictive speech decoder

The concealment procedure used by CELP speech decoders to regenerate lost frames introduces an error that propagates into the following frames. Within the context of voice transmission over packet networks, some packets arrive too late to be decoded and must also be concealed. Once they arrive however, those packets can be used to update the internal state of the decoder, which stops error propagation. Yet, care must be taken to ensure a smooth transition between the concealed frame and the following “updated” frame computed with properly updated internal states. During voiced or quasi-periodic segments, the pitch phase error that is generally introduced by the concealment procedure makes it difficult and detrimental to quality to use the traditional fade-in, fade-out approach. This paper presents a method to handle that pitch phase error. Specifically, the transition is done in such a way that the natural pitch periodicity of the speech signal is not broken.