The relation between speech transmission index, clarity, and reverberation time and listening difficulty in the impulse response database of AIJ

Abstract

The Speech Communication Research Working Group of AIJ (Architectural Institute of Japan) is collecting information on rooms including digitized impulse responses (IRs) to establish a database for evaluating and designing the speech transmission quality of rooms. This database consists of 966 measured IRs. This study presents the relationships between speech transmission index (STI), clarity (Cx) and reverberation time (T) as measures to consider for the design and evaluation of the speech transmission performance of rooms. The data show a wide range of STI and Cx values for a given T, and the minimum STI at each reverberation time can be obtained by diffused field theory. STI and Cx are seen to be better indicators than T for the design of rooms for speech and that T is not as good. Relationships between STI, Cx, and listening difficulty ratings from previous studies [Proc. of RADS (2004), Proc. of Forum Acusticum, pp. 1713–1718 (2005)] found both STI and Cx can be used as predictors of listening difficulty ratings. Finally, listening difficulty ratings of individual IR in the database are estimated and the distribution of listening difficulty ratings in a variety of rooms are presented as a solid bases to design speech transmission quality of rooms.