Dual-mode quasi-logarithmic quantizer with embedded G.711 codec

Abstract

The G.711 codec has been accepted as a standard for high quality coding in many applications. A dual-mode quantizer, which combines the nonlinear logarithmic quantizer for restricted input signals and G.711 quantizer for unrestricted input signals is proposed in this paper. The parameters of the proposed quantizer are optimized, where the minimal distortion is used as the criterion. It is shown that the optimized version of the proposed quantizer provides 5.4 dB higher SQNR (Signal to Quantization Noise Ratio) compared to G.711 quantizer, or equivalently it performs savings in the bit rate of approximately 0.9 bit/sample for the same signal quality. Although the complexity is slightly increased, we believe that due to the superior performance it can be successfully implemented for high-quality quantization.

Forward Adaptive Dual-Mode Quantizer Based on the First-Degree Spline Approximation and Embedded G.711 Codec

“…where y L,n is the n-th representative level within the L-th segment of the PLCSQ designed for p(x,σ ref ), as defined by (12). Substituting (1), (6) and (10) in (13) as well as (1) and (12) in (14), we derive the following expressions:…”

“…In this section, we propose a novel forward adaptive N-levels DMSQ incorporating two forward adaptive N-levels PLCSQs; one of them being G.711 quantizer (PLCSQs are described in the previous section). Using the similar terminology as in [6][7][8]12], an N-levels PLCSQ having smaller support region is denoted here as the restricted quantizer and it is intended to quantize the frames whose amplitude content falls into its support region. Due to this fact, the restricted quantizer introduces only the granular component of the distortion (see (15)), while the overload one (see (16)) is avoided.…”

“…The design goal in the above mentioned quantization schemes were reducing the bit rate subject to the constraint that high quality coding is enabled. Furthermore, a non-adapive (designed for the particular variance and the Laplacian source) dual-mode quantization model that uses a μ-law scalar companding quantizer as a restricted quantizer and G.711 quantizer [11] as the unrestricted quantizer has been proposed in [12]. This paper proposes a novel model of dual-mode quantizer with embedded G.711 quantizer for the Laplacian source that is further implemented in forward adaptive scheme (i.e.…”

“…In regard to the previous DMSQ solutions [6][7][8]12], our novel model uses the spline functions [19] and frame/subframe method to process the input signal. Firstdegree spline function is used to approximate the nonlinear μ-law compression function, which greatly simplifies the practical realization of the compression function.…”

“…Furthermore, the increased performance in terms of average SQNR over similar forward adaptive solutions having the same number of levels is also indicated. In addition to the theoretical results, which have been provided in the majority of DMSQ models developed so far [6,8,12], an experimental analysis using speech signal extracted from the TIMIT database [20] is provided in this paper as well, which is an additional progressive step with respect to former solutions.…”