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Effects of Degradations' Distribution in a Corpus Test on Auditory Ratings
Zitatschlüssel 2008c
Buchtitel Proceedings of the 155th Meeting of the Acoustical Society of America(ASA) / 5th Forum Acusticum / 9e Congrés Français d'Acoustique / 2nd ASA-EAA Joint Conference (Acoustics'08 Paris)
Jahr 2008
Ort Paris, France
Adresse Paris, France
Monat jun
Zusammenfassung Speech quality of telecommunication systems is usually evaluated thanks to auditory tests, which must be carried out in accordance with ITU-T Recommendations. In these tests, subjects are asked to assess the quality of speech sample by giving a score on a five-level scale. The averaging of subjects' scores yields the Mean Opinion Score (MOS) which represents the speech quality for a given condition. However, MOS values can be strongly influenced by many factors. In this paper, we focus on a specific bias, the distribution of the impairments in the corpus test by considering three degradation types: bandwidth (or frequency content), continuity and noisiness. In the specific case of frequency content, the rating of a narrow-band condition may have a lower quality score in a mixed-band corpus (mixed of narrow-band and wideband conditions) than in a purely narrow-band corpus. Consequently, the validity of MOS values is theoretically limited within a test which prevents MOS comparison between different tests. Finally, two suggestions are proposed to limit or avoid this effect: first, an improvement of auditory tests methodology and then, a new approach to assess speech quality, based on the subject behaviour.
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