Performance enhanced scalable wideband speech coding for IP networks

The scalable wideband speech coding scheme based on the Internet low bitrate codec (iLBC) was previously presented and achieved speech quality equivalent to ITU-T G.729.1 at high bit rates. However, the performance was limited at low bit rates. In this paper, we present various approaches to improve performance especially at low bit rates. In particular, the time-domain bandwidth extension (TDBWE) is employed for higher-band coding, and the efficient coding structure is employed in enhancement layers. The performance evaluation results show that significant improvement is achieved at low bit rates and the proposed codec outperforms G.729.1 at most bit rates.