Speech perception in telephone situations under ambient noise conditions

Abstract

In a telephone situation, the partners of a conversation generally experience ambient noise because they are located in acoustically realistic environments. The impact of the ambient noise on the quality of a telecommunication service is a double one: on the one hand, the noise deteriorates the acoustical speech signal either directly or via the sidetone path of a telephone handset, thus leading to lower intelligibility and overall quality. On the other hand, it distracts the listener’s attention. Models which try to predict the effect of ambient noise for telephone network planning purposes in general only regard a diffuse room noise level. However, localization of possible ambient noise sources can help the listener to concentrate on the conversation rather than being distracted by the noise. A conversation test has been carried out in order to investigate the effect of ambient noise in both handset and hands-free telephone situations. Noise was either diffuse or localized at different positions relative to the listener. The test results are compared to intelligibility measures for masked speech given in literature. The investigation can help to quantify the impact of localized ambient noise and gives information to design realistic ambient noise environments for telephone or teleconferencing scenarios.