Currently objective me*asures for predicting the intelligibility of speech are modelled as a linear summation of the contribution of individual frequency bands. The Articulation Index (AI, French and Steinberg, 1947) and Speech Transmission Index (STI, Steeneken and Houtgast, 1980) are based on such a model. There is evidence that this concept is not correct for conditions with gaps or selective masking present in the frequency domain. We designed an experiment where the contribution of individual frequency bands is studied. For this purpose the speech signal is subdivided into seven octave bands ranging from 125 Hz to 8 kHz. For 26 different combinations of minimal three octave bands the CVC-word score (Consonant-Vowel-Consonant, nonsense words) was obtained at three signal-to-noise ratios. A revised model, which accounts for mutual dependency between adjacent octave bands by the introduction of a so-called redundancy factor will be proposed. Consequences for the existing objective measures are discussed.
Bibliographic reference. Steeneken, Herman J. M. / Houtgast, Tammo (1991): "On the mutual dependency of octave-band-specific contributions to speech intelligibility", In EUROSPEECH-1991, 1133-1136.