Wideband speech coding using ADPCM and a new enhanced bandwidth extension method

An enhanced bandwidth extension scheme is introduced in this paper for wideband speech coding using ADPCM. The coded lower band signal plus small side information (some parameters) are transmitted instead of the whole band. In the decoder both frequency parts are reconstructed from the coded signal and the received parameters. In the proposed method, the high frequency part is derived from the excitation signal of the low frequency part and the received spectral information in the form of vector quantized LPC. Optimum codebook element is chosen, among candidates, that when used in conjunction with the lower frequency part excitation best matches the high frequency signal. The search is carried out in a sorted codebook and the index of the chosen element is transmitted as a Huffman code. The results show that 23% reduction in the bit rate is achieved, in comparison with G.722 standard, bearing no degradation in quality.