Bandwidth Extension of a Narrowband Speech Coder for Music Streaming Services Over IP Networks

In this paper, we propose a bandwidth extension (BWE) algorithm for a low-bit-rate narrowband CELP coder using a spectral envelope sharing approach to develop a wideband speech coder. The developed wideband speech coder, referred to here as the BWE coder, is constructed using an embedded structure by adding an enhancement layer to the narrowband CELP coder. To minimize the bit-rate increase caused by the enhancement layer, the proposed BWE coder shares the spectral envelope and excitation parameters both with the narrowband CELP coder and the enhancement layer. In this paper, we choose G.729EV layer 2 as the baseline narrowband speech coder, and mel-frequency cepstral coefficients (MFCCs) are used to reconstruct the higher frequency components at the enhancement layer. By doing this, the bit-rate of the proposed BWE coder is found to be 12.7 kbit/s, just 0.7 kbit/s higher than that of G.729EV layer 2. It is also demonstrated from a MUSHRA test with audio signals from four different music genres, that the BWE coder gives better quality than G.729EV layer 2 and comparable quality to G.729EV layer 3, corresponding to an overall bit-rate reduction of 1.3 kbit/s.