A packet loss concealment method using pitch waveform repetition and internal state update on the decoded speech for the sub-band ADPCM wideband speech codec

The paper proposes a packet loss concealment (PLC) method for the SB-ADPCM (sub-band adaptive differential pulse code modulation) wideband speech codec. When a packet loss occurs, the concealment repeats a pitch waveform of the speech decoded in the past with attenuation to generate a speech waveform corresponding to the lost packet. The packet loss causes differences in the internal states, such as prediction filter states, between encoding and decoding of the SB-ADPCM codec. This difference results in an annoying click noise during the period following the packet loss. The proposed method reduces this difference by updating the internal state based on the speech decoded by the concealment in the past. It also employs a forgetting factor control for the internal states, which reduces the impact on the internal states from the packet loss. Results from a five-grade mean opinion test show that the proposed method achieves around 3 (fair) or 4 (good) speech quality at a loss rate lower than 5%, and 0.4 through 1.0 higher quality compared to the conventional muting PLC method at packet loss rates of 1 to 10% with a packet size of 10 or 20 msec.