A 16-kbit/s wideband speech codec scalable with g.729

A wideband speech scalable codec is proposed for improving the flexibility in telecommunication networks. This coder is scalable with G.729 (ITU 8-kbit/s standard). Its decoder can process the incoming bitstream at three bit rates (8, 12, and 16 kbit/s) and provide a choice of speech types (wideband and telephone-band). The codec has a split-band structure, where both bands are coded by analysis-by-synthesis techniques. This paper proposes two types of scalable codec: a separate one and a composite one. It also proposes a new method (an additional adaptive codebook) for predicting pitch, while maintaining scalability with the G.729 codec. Subjective testing for wideband speech showed that the quality of the proposed codec at 16-kbit/s is equivalent to that of the 64-kbit/s G.722, and at 12-kbit/s is better than that of the 48-kbit/s G.722. Testing has further demonstrated that the 8-kbit/s coder provides high quality for telephone-band speech.