The Speech Transmission Index (STI) , and the Room Acoustical STI (RASTI) , have been internationally accepted as objective standards for the prediction of the intelligibility of speech communication channels, . Recently, the applicability, diagnostic power, and prediction accuracy of these indices have been further extended . These extensions include the possibility to predict the speech intelligibility for both male and female speech, and for individual phoneme groups (plosives, fricatives, vowel-like consonants, and vowels). Based on the improved algorithm and on the experience obtained with the existing STI-measuring devices (25 systems were installed in other laboratories), a new development was initiated for a software based measuring system with standard equipment (personal computer with data-acquisition). This resulted in a software package which is system independent. The paper describes the improvement of the STI, the new measuring method, and will also give some examples of the applications (electro-acoustical transducers, and a telephone communication channel). The method can also be used to specify the input conditions for speech recognition systems.
Bibliographic reference. Steeneken, Herman J. M. / Verhave, J. A. / Houtgast, Tammo (1993): "Objective assessment of speech communication systems; introduction of a software based procedure", In EUROSPEECH'93, 203-206.