The Speech Transmission Index (STI) has been shown to be an accurate predictor of speech intelligibility in auditoria, and the computationally more efficient RASTI method has recently become an official International Electrotechnical Commission (IEC) standard. While instruments have been developed by others to measure the STI after room construction is complete and the sound system is operating, until now the STI method has not been implemented and tested in a sound system modeling program. Such an implementation has a fundamental advantage in that it does not require acoustic measurements from the room as input; this means that intellibility can be predicted in unbuilt or inaccessible rooms solely on the basis of modeled rather than actual behavior. In this study, a new microcomputer-based implementation of the STI method is described along with the results of an experiment designed to test its accuracy. The accuracy of the new method is shown to be essentially the same as the accuracy of predictions based on in-room measurements. These results show that speech intelligibility can be accurately predicted without using acoustic measurements.
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