Subjective and objective assessment of full bandwidth speech quality

Abstract

With the introduction of fullband speech coding the question arises what role frequency components above 14 kHz play in speech quality assessment. On the one hand, our results show that bandwidth limitation from 24 kHz down to 14 kHz is not audible to even the most critical subject. On the other hand, 14-24 kHz band limited, audible levels of noise clearly decrease the perceived quality, especially for young subjects with healthy ears. Furthermore, modern high-quality voice links, using the latest speech codecs, often apply advanced buffering schemes that introduce a new type of audible degradation: Micropauses. We investigated the impact of i) bandwidth limitation, ii) coding schemes, iii) micropause, and iv) noise on the perceived quality. Subjective results and objective predictions based on ITU-T recommendation P.863 POLQA are compared. For accurate prediction of the impact of micropauses and noise degradations small model adaptations are suggested. In contrast codec degradations and bandwidth limitation are already predicted with very high accuracy by POLQA: R = 0.98, RMSE= 0.05 Mean Opinion Score (MOS).