Validation of the Rapid Speech Transmission Index (Rasti) in a Classroom Environment

Because the acoustics of a room have a substantial impact on speech intelligibility, researchers have tried over the years to develop the most effective way to evaluate the effects of the acoustic environment on speech intelligibility. Both subjective and objective measures of speech intelligibility have been devised. For the purposes of this study, subjective measures are those in which a speech recognition test is given to a group of subjects whose scores provide a direct indication of speech intelligibility at each position in the listening environment {Steeneken & Houtgast, 1980). Objective measures are those that determine the acoustic factors that affect speech intelligibility in a room, and through the use of a formula or calculation scheme, determine the loss of speech intelligibility in a room (Rao, 1992) . Subjective measures are useful in that they have high face validity, but they require trained listeners and speakers. They can become expensive and also can take a long time to do (Rao, 1992). Objective measures are less time consuming and less expensive, but their face validity is low. Because of the ease of using objective measures, researchers have attempted to prove their validity by comparing them with subjective measures (Houtgast, 1981; Houtgast & Steeneken, 1984)