Low complexity ACELP coding of 7 kHz speech and audio at 16 kbps

Abstract

The 7 kHz audio bandwidth is increasingly being considered for natural quality communications, especially for binaural, hands-free listening situations such as in teleconferencing and digital AM broadcasting. Based on detailed performance comparisons of several alternative designs, we shortlisted an ACELP-based 7 kHz coder design for performance optimization. This paper presents several low-complexity design strategies which significantly reduce the computational complexity of the encoder and decoder while not compromising on the reconstructed signal quality. These include: (a) open-loop pitch estimation and reduced search adaptive codebook; (b) open-loop pitch estimation based on pre-search in downsampled signal domain; (c) LSF quantization using a combination of scalar and vector quantization; (d) a novel reduced complexity search of algebraic codebook; and (e) efficient postfiltering in the decoder. The computational complexity of the encoder and decoder modules of three ACELP coders with different bit allocations are compared.