Fast Recovery for a CELP-Like Speech Codec After a Frame Erasure

• Published in: IEEE transactions on audio, speech, and language processing speech, and language processing, 2007-11, Vol.15 (8), p.2485-2495
• Main Authors: Chibani, M., Lefebvre, R., Gournay, P.
• Format: Article
• Language: English
• Subjects: Adaptive codebook; Applied sciences; Bit rate; Code standards; code-excited linear prediction (CELP); Codec; Coding, codes; Costs; Decoders; Decoding; error propagation; Exact sciences and technology; Excitation; frame erasure; Frames; Information, signal and communications theory; Internet telephony; Mathematical models; Programmable control; Quality of service; Recovery; Signal and communications theory; Signal processing; Speech; Speech codecs; Speech processing; Studies; Technological innovation; Telecommunications and information theory; Wideband; wideband speech coding
• ISSN: 1558-7916; 2329-9290; 1558-7924; 2329-9304
• DOI: 10.1109/TASL.2007.907332

The adaptive codebook used in code-excited linear prediction (CELP)-like speech codecs is very effective for modeling the quasi-periodic component of the excitation signal but, unfortunately, introduces a strong interframe dependency that renders the decoder vulnerable to frame erasures. For voiced speech, the error affects not only the erased frame but also all the subsequent frames. In this paper, a technique to improve the recovery after a frame erasure is proposed. The technique consists in a constrained excitation search at the encoder and a resynchronization procedure at the decoder. The constraint aims at reducing the contribution of the adaptive codebook by making the innovation codebook partially model the pitch excitation. Further, for highly voiced frames, the pitch-related information contained in the innovation excitation is exploited at the decoder to speed up the resynchronization of the adaptive codebook after a frame erasure. When applied to the adaptive multirate wideband (AMR-WB) codec, the method brings a significant improvement in the case of frame erasures, at the cost of a minor quality loss compared to the standard codec at the same bit rate. The method does not need additional delay and has the advantage of maintaining full interoperability between the standard codec and its modified version.