Accuracy of Evaluation of Speech Transmission Index with Formant-Modulation Method

Abstract

Unlike the known modulation method, the formant-modulation method for the evaluation of speech intelligibility allows the evaluation of not only the speech transmission index but also the articulation index. This paper presents the results of a study of the accuracy of speech transmission index evaluation using the full and rapid variants of the formant-modulation method. The study is carried out by the computer simulation method for two cases, namely, the case of the predominant effect of noise interference and the combined effect of noise and reverberation in a room of medium volume. Dependences of the systematic and random components of the estimation error of speech transmission index on the duration of the test signal and signal-to-noise ratio are obtained. It is shown that although the fast version of the formant-modulation method is 4–5 times inferior to the full version in terms of measurement accuracy of the speech transmission index, the desired estimation accuracy can be achieved if the duration of the test signal is sufficiently long. In particular, the bias and standard deviation of the estimate of the speech transmission index obtained by the fast formant modulation method do not exceed 0.03 and 0.014, respectively, for the test signal duration of 16 s.