Comparison of basic and simplified sequential algorithms for the computation of lattice filter predictor coefficients in ADPCM coding of speech

In the view of transmitting telephone speech signals at the bit rate of 32 kbit/s, the implementation of a predictor with lattice filters has been investigated instead of the classical gradient updated transversal filter commonly used in ADPCM coders. Several simplified methods for updating the lattice filters have been developed. Then those codecs are compared against the standard PCM 64 kbit/s, the PCM 56 kbit/s, the fixed predictor and the gradient updated ADPCM coders at 32 kbit/s on a subjective scale derived from listening tests. The improvement given by the adaptive predictors over fixed ones clearly appears. It is also shown that the simplified lattice ADPCM coders perform significantly better than the non simplified ones for high bit error rates (10^-4or 10^-3). Another feature of the algorithms developed here is their simplicity that makes them suitable for hardware and VLSI implementation not only for ADPCM coding but also for the speech analysis part in linear predictive vocoders.