Speech coding is a very mature research area and many coding schemes are available that provide speech qualities ranging from highly intelligible synthetic speech at about 2 kbit/s, till wideband natural speech at about 16 kbit/s. However, emerging application scenarios such as information services on broadcast radio are eliciting additional concurrent challenges not easily addressed by current speech coding technology, namely the need to code mixed audio material, the need to permit flexible bitrate coding configurations, the need to scale effectively in quality in the range 2-8 kbit/s, and the need to offer pleasant natural sound. In this paper we present a new very low rate speech/audio coding technology addressing those concurrent challenges thanks to the use of innovative approaches regarding accurate reconstruction of harmonic complexes, optimal coding of the excitation, efficient side information coding, and suitable combination of new bandwidth extension techniques. The structure of the speech/audio coder will be detailed and its performance in the range 2.4-12 kbit/s will be illustrated and compared to that of reference coders.
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