Safety-net pyramid VQ of LSF parameters for wideband speech codecs

The authors propose a predictive pyramid VQ (PPVQ) that uses the safety-net concept to quantise the LSF parameters of wideband speech. A first-order auto-regressive (AR) predictor is used to predict the LSF parameters. To quantise the prediction error signal effectively, a pyramid VQ (PVQ) is used while a memoryless PVQ is used to encode low-correlation frames. By combining the PPVQ and the memoryless PVQ, denoted `safety-net pyramid VQ´, the advantages of both quantisation methods can be utilised. The average SD value of a safety-net pyramid VQ is 0.35 dB less than that of a predictive split VQ (PSVQ). The safety-net pyramid VQ also requires low complexity and does not require any memory for the codebook storage