Quality Dimensions of Narrowband and Wideband Speech Transmission

The study presented in this paper aims at exploring the perceptual spaces evoked for users of two different telephone scenarios: traditional narrowband speech transmission, and mixed narrowband/wideband speech transmission that may be encountered in today's Voice-over-IP services. Underlying dimensions that constitute the skeleton of these spaces are revealed by auditory experiments, following two different paradigms of judgment: a) Similarity-scaling, and b) Attribute-scaling (Semantic Differential) with subsequent a) Multidimensional Scaling, and b) Principal Component Analysis of a diverse set of stimuli. Similar configurations are obtained which are unequivocally interpretable. Three common dimensions, valid for both the narrowband and the wideband scenario can be identified: "Discontinuity", "Noisiness", and "Coloration". In addition, the wideband space is extended by a further, wideband-specific dimension. Integral listening-quality can well be modeled by means of these dimensions. In both scenarios, "Discontinuity" represents the most important quality feature. The presented work forms the basis for instrumental diagnostic quality measures.