Subjective and objective measurement of synthesized speech intelligibility in modern telephone conditions

• All the investigated telecom degradations seriously impact the subjective intelligibility of synthesized speech.
• PESQ Intelligibility is not capable to provide valid intelligibility predictions.
• POLQA Intelligibility is capable of providing good intelligibility predictions.

This paper investigates the impact of different telephone channels, represented by impairments as introduced by modern telecommunication networks (e.g. speech coding, bandwidth limitation, packet loss, etc.), on the intelligibility of synthesized speech. Both subjective and objective assessments are used. Two different speech intelligibility prediction models, namely PESQ Intelligibility and POLQA Intelligibility, are evaluated by comparing the predictions with subjectively obtained intelligibility scores. The results show that all the investigated degradations seriously impact the intelligibility of the synthesized speech measured subjectively. Furthermore it is shown that PESQ Intelligibility provides too low correlations between predicted objective measurements and subjective scores for accurate prediction of speech intelligibility while POLQA Intelligibility is capable of providing good intelligibility predictions in the case that a closed response experimental set up is used.