Low-complexity Bandwidth Extension in MDCT domain for low-bitrate speech coding

We propose a low-complexity bandwidth extension (BWE) method operating in the modified discrete cosine transform (MDCT) domain to reduce the bitrate of wideband and super-wideband speech codecs. The proposed method generates a high-frequency signal by copying the MDCT spectrum from the low frequency part, and then adjusts tonality to improve the subjective quality of the generated high-frequency signal. In combination with an MDCT-based transform codec, it requires only 64.9% of the computational complexity of MPEG-4 spectral band replication (SBR). It also achieves subjective quality better than SBR for many speech samples.