This paper consists of a study on the influence of the loudness on the perceived quality of transmitted speech. This quality is based on judgments of particular quality features, one of which is loudness. In order to determine the influence of loudness on perceived speech quality, we designed a two-step auditory experiment. We varied the speech level of selected speech samples and degraded them by coding and packet-loss. Results show that loudness has an effect on the overall speech quality, but that effect depends on the other impairments involved in the transmission path, and especially on the bandwidth of the transmitted speech. We tried to predict the auditory judgments with two quality prediction models. The signal-based WB-PESQ model, which normalizes the speech signals to a constant speech level, does not succeed in predicting the speech quality for speech signals with only impairments due to a non-optimum speech level. However, the parametric E-model, which includes a measure of the listening level, provides a good estimation of the speech quality.
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