Measurement and prediction of speech intelligibility in noise and reverberation for different sentence materials, speakers, and languages

The present study investigates the role of the speech material type, speaker, and language for speech intelligibility in noise and reverberation. The experimental data are compared to predictions of the speech transmission index. First, the effect of noise only, reverberation only, and the combination of noise and reverberation was systematically investigated for two types of sentence tests. The hypothesis to be tested was that speech intelligibility is more affected by reverberation when using an open-set speech material consisting of everyday sentences than when using a closed-set test with syntactically fixed and semantically unpredictable sentences. In order to distinguish between the effect of speaker and language on speech intelligibility in noise and reverberation, the closed-set speech material was recorded using bilingual speakers of German-Spanish and German-Russian. The experimental data confirmed that the effect of reverberation was stronger for an open-set test than for a closed-set test. However, this cannot be predicted by the speech transmission index. Furthermore, the inter-language differences in speech reception thresholds were on average up to 5 dB, whereas inter-talker differences were of about 3 dB. The Spanish language suffered more under reverberation than German and Russian, what again challenged the predictions of the speech transmission index