speech intelligibility (acoustics)
Speech intelligibility is spoken of in communication and also in the acoustic irradiation of rooms. In communication, intelligibility is influenced by coding methods, bandwidths, sampling rates, resolutions, delay times, bit error rates, echoes and jitter, whereas in acoustics, speech quality in sounded rooms is influenced by the shape of the room, room size, reflections, absorptions, background noise, radiation characteristics of the loudspeakers, position of the absorbers and the listener.
As early as the 1960s, methods for evaluating subjective speech intelligibility were developed. One of the first procedures was the Diagnostic Rhyme Test( DRT), which used rhyming words and was used in the U.S. military. An improved version of the DRT procedure was the Modified Rhyme Test (MRT), which was followed in the 1970s by Diagnostic Acceptability Measure( DAM) and Diagnostic Communicability Test( DCT). Further development led to the Diagnostic Alliteration Test( DAT) in the 1980s.
The best known and most frequently used evaluation method for the speech quality of telephony is the Mean Opinion Score( MOS), which is calculated from the mean evaluation of different speech patterns by several persons.
As far as the sound reinforcement of rooms is concerned, the reverberation time is a major factor that decisively affects audibility. The shorter the reverberation time, the better the speech intelligibility in a room. If the reverberation time is long, the reverberation can impair the following syllable and thus worsen speech intelligibility.
There are several machine and static methods for evaluating rooms exposed to sound. These include the Speech TransmissionIndex( STI), Rapid Speech Transmission Index( RASTI), Speech Intelligibility Index( SII), the aged Articulation Index( AI), and ALcons, which is concerned with articulation loss in consonants.