Blind method of estimating speech transmission index from reverberant speech signals

The speech transmission index (STI) is an objective measurement that is used to assess the quality of speech transmission as well as listening difficulty in room acoustics. This paper proposes a specified method of blindly estimating the STI from observed reverberant speech signals, based on the concept of the modulation transfer function. The proposed method has been developed from a simplified method that the authors previously reported, to resolve three issues: (1) whether the method could estimate STIs even if the room impulse response could not be approximated as Schroeder's model, (2) whether the method could not only correctly estimate STIs from reverberant AM but also reverberant speech signals, and (3) whether the method could estimate STIs from observed signals in reverberant environments where people cannot be excluded. Simulations were carried out to verify the first two issues, by using both AM and speech signals in reverberant environments. Experiments were also carried out in several rooms, which a few people were in, to verify the last issue. The results revealed that the proposed approach could be used to effectively estimate STIs from reverberant speech signals in various room acoustics even if people were in the room.