High-quality Laplacian source quantisation using a combination of restricted and unrestricted logarithmic quantisers

This study proposes a quantiser, named the combined quantiser, composed of two forward adaptive μ-law quantisers (FAμQs), one designed to quantise signals having restricted amplitude dynamics and the other designed for unrestricted signals. The combined quantiser performs frame-by-frame analysis of the input signal, according to which, for each frame procession, it selects one of the two disposable FAμQs. In order to exploit the higher density of the restricted FAμQμs quantisation levels, the restricted FAμQ is selected when all amplitudes of samples within a frame belong to the restricted FAμQμs support region. Otherwise, the unrestricted FAμQ having the same number of quantisation levels, but a wider support region is selected. To provide a more frequent selection of the restricted FAμQ than the unrestricted one, the disposable quantisers´ support region thresholds are determined to satisfy the total distortion minimisation criterion. The authors show that the combined quantiser designed for the Laplacian source provides gain in the signal to quantisation noise ratio and in the compression over the G.711 quantiser as well as satisfies G.712 Recommendation for high-quality quantisation. This indicates the possibility of practical application of the combined quantiser in the contemporary transmission of Laplacian source signals.