Scalable multi-rate iLBC

Rate flexibility and high robustness to packet loss are the essential features of speech codec for voice communications over Internet Protocol (IP) networks. Multi-rate internet Low Bit-rate Codec (iLBC) is one of the speech codecs that possesses both properties and was presented by our previous papers. However the speech quality is limited in clean channel conditions because of the limitations of the current frame-independent coding scheme in time domain. In this paper, the benefits of scalable structure constructed by the addition of enhancement layer to the core layer of multi-rate iLBC are presented. The experimental simulation results show that the proposed framework can improve speech quality especially at high bit rates.