A backward‐type band‐split adaptive predictive coding system with dynamic bit allocation for wideband speech and sound signals

Abstract

This paper proposes a new backward‐type speech coding system (ADPCM‐AB) for wideband (7 kHz) speech and sound signals. In this system, a split‐band adaptive predictive coding scheme with gradient PARCOR lattice filter and a dynamic bit allocation scheme are employed, where quantization bits are dynamically allocated over the subbands (frequency), the subintervals (time), and the channels (stereo) in accordance with the distribution of the residual energies. They serve to remove the redundancies due to the periodic concentration of the prediction residual energy and the nonuniform nature of the speech spectrum. The ADPCM‐AB needs neither longer delay time than 4 ms nor transmission of side information parameters because the parameters for predictive coding and dynamic bit allocation are calculated with the locally decoded signals. It is clarified that the ADPCM‐AB system has the best speech quality among the conventional backward‐type coding systems. It is also shown that this system provides speech quality subjectively equivalent to 11‐bit linear PCM (176 kb/s) at 64 kb/s.