Frequency selectivity as a function of level and frequency measured with uniformly exciting notched noise

Thresholds for detecting sinusoidal signals were measured as a function of the spectral width of a notch in a noise masker. The notch was positioned b oth symmetrically and asymmetrically around the signal frequency. The noise was designed to create equal excitation per ERB within its passbands (unif ormly exciting noise), after allowing for the transfer function of the head phone and the middle ear. For a signal frequency of 250 Hz, the level per E RB ranged from 35 to 80 dB in 15-dB steps. For signal frequencies of 500, 1 000, 2000, and 4000 Hz, the level per ERB ranged from 40 to 70 dB per ERB i n 15-dB steps. Auditory filter shapes were derived from the data by modelin g the auditory filter as the sum of a sharply tuned tip tilter and a broade r tail filter. The gain of the tip filter was assumed to be a function of l evel. The shape of the tip filter and the gain and shape of the tail filter were assumed to be level independent. The data for all levels were fitted simultaneously. The data were fitted best when the gain of the tip filter w as assumed to be a function of the signal level las opposed to the masker l evel per ERB). The filter shapes showed a level dependence that qualitative ly resembled the level dependence of filtering on the basilar membrane. The maximum gain of the tip filter tended to increase with increasing center f requency up to 1 kHz, but to remain roughly constant for higher frequencies . (C) 2000 Acoustical Society of America. (S000-4966(00)03211-2].