Quality assessment of speech codecs in synchronous e-learning environments

Synchronous e-learning tools always include an audio-conference feature so participants in e-learning sessions can communicate orally. Audio quality is critical to avoid misunderstandings and improve user experience. Therefore, it is important to evaluate the audio quality that speech codecs can provide. Few existing assessment works consider the resources consumed (CPU or bitrate) to provide the audio quality, although synchronous e-learning sessions usually involve various participants, making resource consumption an important issue. In this paper, both objective and subjective audio quality measurement methods are used to characterize and estimate the audio quality of twenty speech codecs as a function of the resources consumed during synchronous e-learning sessions. Although users' opinions on audio quality are often more pessimistic than the evaluation provided by objective measurements, the correlation between objective and subjective measurements is high for medium-quality codecs. Users perceive lower audio quality for low-quality codecs than indicated by objective measurements, while they are not able to identify high-quality codecs, scoring them similarly to medium-quality codecs.