Application of quadrature mirror filters to split band voice coding schemes

TLDR

The paper examines sub‑band voice coding using QMF, detailing two sub‑band splits and two coding schemes at 16 kbps and 32 kbps. The study investigates the use of Quadrature Mirror Filters for sub‑band voice coding. QMF is employed to prevent aliasing during sub‑band splitting, after which each sub‑band is independently encoded with Block Companded PCM quantizers and bits are allocated adaptively to exploit perceptual error weighting. The proposed scheme achieves higher average S/N ratios for male and female voices compared to conventional BCPCM and CCITT A‑Law coding. Taped results will be presented at the conference.

Abstract

This paper deals with applications of Quadrature Mirror Filters (QMF) to coding of voice signal in sub-bands. Use of QMF's enables to avoid the aliasing effects due to samples decimation when signal is split into sub-bands. Each sub-band is then coded independently with use of Block Companded PCM (BCPCM) quantizers. Then a variable number of bits is allocated to each sub-band quantizer in order to take advantage of the relative perceptual effect of the quantizing error. The paper is organized as follows: - First, splitting in two sub-bands with QMF's is analysed. -Then, a general description of a splitband voice coding scheme using QMF's is made. -Finally, two coding schemes are considered, operating respectively at 16 KBps and 32 KBps. Averaged values of S/N performances are given when encoding both male and female voices. Comparisons are made with conventional BCPCM and CCITT A-Law. Taped results will be played at the conference.