A 16 kbit/s wideband CELP coder with a high-order backward predictor and its fast coefficient calculation

This paper proposes a 16 kbit/s wideband CELP coder with a high-order backward predictor and its fast coefficient calculation method. The coefficients are calculated from autocorrelations of the residual signal. The proposed calculation scheme approximately calculates the autocorrelations of the residual signal from those of the decoded output signal. Therefore, an inverse filtering of the decoded output signal and a calculation for the autocorrelations of the residual signal are not necessary, and the complexity for the backward prediction is drastically reduced. The proposed coder also adopts a multi-pulse vector quantization to efficiently represent an excitation signal as well as a multi-mode coding to enhance the performance and the channel error robustness. An MOS test shows that the proposed coder achieves superior performance for speech to that of ITU-T G.722 at 56 kbit/s and comparable performance for audio to that of G.722 at 48 kbit/s