Rating reverberation.

A speaker's thundering voice, echoing through a great hall, can sound dramatic, but too much reverberation often makes it practically impossible for listeners to understand what the speaker is saying. Until recently, evaluating such problems in places like theaters, lecture rooms, churches, train stations and airplanes involved time-consuming experiments and subjective judgments. Now a Danish company has developed an electronic technique for measuring speech intelligibility objectively and quickly.

In the RASTI (rapid speech transmission index) method, a portable transmitter located where a speaker would stand sends out a special test signal that sounds a little like a chugging train. A small receiver placed at the listener's position captures and analyzes the sound, and within 10 seconds calculates and displays a speech intelligibility rating.

The method was tested in a Copenhagen church with a very long reverberation time. The measurements corresponded very well with reports from the church congregation, says Klaus Hojbjerg of Bruel & Kjaer in Naerum, Denmark. He described the RASTI method at a recent Acoustical Society of America meeting in Nashville, Tenn. Using the new method, Hojbjerg was able to take 400 measurements and get a complete picture in just one day. An earlier study, applying a subjective method, had taken two weeks.