Switched split vector quantisation of line spectral frequencies for wideband speech coding

In this paper, we investigate the use of the switched split vector quantiser (SSVQ) for coding short-term spectral envelope information for wideband speech coding. The SSVQ is the hybrid of a switch vector quantiser and split vector quantiser, which has been shown in previous studies to be more efficient, in terms of rate-distortion, as well as possessing low computational complexity, than the split vector quantiser. In our experiments, the SSVQ is used to quantise line spectral frequencies from the TIMIT database and its spectral distortion performance is compared with the split vector quantiser, the split-multistage vector quantiser (S-MSVQ) with MA predictor from the AMRWB speech coder (ITU-T G.722.2), and PDF-optimised scalar quantisers. We show the SSVQ, which is a memoryless scheme, to achieve comparable spectral distortion to the S-MSVQ with MA predictor at 46 bits/frame. The five-part SSVQ requires 42 bits/frame and 17.7 kflops/frame for transparent coding, compared with 46 bits/frame and 40.96 kflops/frame for the five-part split vector quantiser.