A Phonetic Reference Paradigm for Instrumental Speech Quality Assessment of Artificial Speech Bandwidth Extension

Today’s instrumental speech quality measures are limited in their use as they ”do not yet sufficiently include processing steps beyond the periphery of the auditory system” [1]. This becomes particularly obvious when using reference-based instrumental methods to assess the quality of artificial speech bandwidth extension (ABWE) approaches. While Blauert and Jekosch [1] have not proposed particular schemes, they advocate a model of sound quality representing layers of abstraction. In fact, once subjects are asked for opinion scores following any of ITU-T’s definitions, they have already understood (or not)what was spoken. It is our firm conviction that in nottoo-bad testing conditions this knowledge serves as internal reference for judging speech quality – which in consequence asks for a paradigm shift of reference-based instrumental speech quality measures. In consequence, not only some (direct wideband) reference speech data is useful, but also a phonetic transcription of the speech, serving as human-internal representation of what was spoken. The paper will give thoughts to support this thesis, along with a proof that not all sounds are equal, asking for a phoneme-specific processing of future reference-based instrumental speech quality assessment methods.