A 16-kbit/s bandwidth scalable audio coder based on the G.729 standard

This paper proposes a bandwidth-scalable coding scheme based on the G.729 standard as a base layer coder. In the scheme, according to the channel conditions, the output speech of the decoder can be selected to be narrow-band (4-kHz bandwidth) or wideband (8-kHz bandwidth). The proposed scheme consists of two layers: base and enhancement. The base coder uses the G.729 algorithm to encode narrow-band speech. The enhancement coder is based on a fullband CELP model and it encodes wideband speech while making use of the available base layer information. Two bandwidth-scalable coders are designed: one is scalable with the 8 kb/s G.729 base coder and another with the 6.4 kb/s G.729 (Annex D) base coder. Subjective tests show that, for wideband speech, the proposed coders at 16 kb/s achieve better performance than the 16 kb/s MPEG-4 CELP with bandwidth scalability.