Intelligibility of 1/3-octave speech: Greater contribution of frequencies outside than inside the nominal passband

We reported previously that "everyday" sentences were highly intelligible w hen limited to a 1/3-octave passband centered at 1,500 Hz and having transi tion-band slopes of approximately 100 dB/octave. The present study determin ed the relative contributions to intelligibility made by the passband (PB) and the transition bands (TBs) by partitioning the same bandpass sentences using 2,000-order FIR filtering. Intelligibility scores were: PB with both TBs, 92%; deletion of both TBs (leaving only the 1/3-octave PB with nearly vertical slopes), 24%; deletion of the PB (leaving both TBs separated by a 1/3-octave gap), 83%. These and other results indicate a remarkable ability to compensate for severe spectral tilt and the consequent importance of co nsidering frequencies outside the nominal passband in interpreting studies using filtered speech. (C) 1999 Acoustical Society of America.