A comparison of LSF and ISP representations for wideband LPC parameter coding using the switched split vector quantiser

In this paper, we apply the switched split vector quantiser (SSVQ) for coding short-term spectral envelope information in wideband speech coding to compare and contrast two LPC parameter representations: line spectral frequencies (LSFs) and immittance spectral pairs (ISPs). 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 lower computational complexity, than the split vector quantiser (SVQ). On the TIMIT database, the five-part SSVQ requires 43 and 44 bits/frame to transparently code LSFs and ISPs, respectively. This 1 bit/frame difference between LSFs and ISPs is also observed in five-part SVQ. The split-multistage vector quantiser (S-MSVQ) with MA predictor from the AMR-WB speech coder (ITU-T G.722.2) is also used as a basis of comparison where we find the SSVQ, which is a memoryless quantisation scheme, to be competitive at 46 bits/frame.