A bandwidth extension (BWE) algorithm from wideband to superwideband (SWB) is proposed for a scalable speech/audio codec\r\nthat uses modified discrete cosine transform (MDCT) coefficients as spectral parameters. The superwideband is first split into\r\nseveral subbands that are represented as gain parameters and normalized MDCT coefficients in the proposed BWE algorithm.\r\nWe then estimate normalized MDCT coefficients of the wideband to be fetched for the superwideband and quantize the fetch\r\nindices. After that, we quantize gain parameters by using relative ratios between adjacent subbands. The proposed BWE algorithm\r\nis embedded into a standard superwideband codec, the SWB extension of G.729.1 Annex E, and its bitrate and quality are compared\r\nwith those of the BWE algorithm already employed in the standard superwideband codec. It is shown from the comparison that\r\nthe proposed BWE algorithm relatively reduces the bitrate by around 19% with better quality, compared to the BWE algorithm in\r\nthe SWB extension of G.729.1 Annex E.
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