Super-Wideband Bandwidth Extension for Wideband Audio Codecs Using Switched Spectral Replication and Pitch Synthesis

This paper describes a new bandwidth extension algorithm which is targeted at high quality audio communication over IP networks. The algorithm is part of the Huawei/ETRI candidate for the ITU-T super-wideband (SWB) extensions of Rec. G.729.1 and G.718. In the SWB candidate codec, the 7-14 kHz frequency band of speech and audio signals is represented in terms of temporal and spectral envelopes. This description is encoded and transmitted to the decoder. In addition, the fine structure of the input signal is analyzed and compactly encoded. From this compact information, the decoder can regenerate the 7-14 kHz fine structure either by spectral replication or by pitch synthesis. Then, an adaptive envelope restoration procedure is employed. The algorithm operates in the MDCT domain to allow subsequent refinement coding by vector quantization of spectral coefficients. In the paper, relevant listening test results for the G.729.1SWB candidate codec that have been obtained during the ITU-T standardization process are summarized. Good audio quality could be shown for both speech and music signals.