Extension of the E-model towards super-wideband speech transmission

In this paper, the quality gain of super-wideband (SWB) speech, transmitted in the much wider frequency range of 50-14000 Hz compared to the standard 300-3400 Hz narrowband, is quantified employing the E-model framework, a parametric tool for speech quality prediction. Based on two listening experiments, a linear extrapolation of the E-model transmission rating scale was found that leads to a maximum quality advantage of 39% relative to wideband (50-7000 Hz) transmission, and 79% relative to narrowband. Furthermore, narrowband, wideband, and super-wideband conditions can be quantified on this universal quality scale. Equipment Impairment Factors were derived and discussed for several SWB codecs. It will further be shown that a model quantifying the quality impact of linear distortions, reflected by the Bandwidth Impairment Factor, can successfully applied to SWB conditions. The correlation between the overall impairment and the model predictions amounts to r = 0.977 for linearly distorted speech samples.