Comparison of auditory filter shapes obtained with notched-noise and noise-tone maskers

The notched-noise method has been widely used to estimate the shape of the auditory filter. Results obtained using this method may be influenced by combination bands produced by the interaction of components within the upper band of noise in the notched-noise masker. To assess the possible effect of such combination bands, results were compared for two types of masker: A notched noise, as used in previous experiments; and a masker in which the upper band of noise was replaced by a sinusoid with a frequency corresponding to the lower edge frequency of that band. This is referred to as the noise-tone masker. The signal frequency was 2 kHz, and measurements were obtained for two different spectrum levels of the noise masker, 30 and 45 dB. Auditory filter shapes derived using the two maskers were similar on their low-frequency sides, as expected. The low-frequency sides were less steep at the higher masker level. The high-frequency sides of the auditory filters derived using the noise-tone masker were sometimes slightly steeper than those obtained using the notched-noise masker, but the effect was generally small. Changes with level on the high-frequency sides were not consistent across subjects. An analysis of the notched-noise data taking into account the effects of the combination bands suggests that the maximal spectrum level of the combination bands, in the region just below the lower spectral edge of the primary noise band, is about 20 to 30 dB below the spectrum level of the primary band. At this relative level, the combination bands have only a very small influence on the high-frequency sides of the derived auditory filters. The influence on the estimated equivalent rectangular bandwidths (ERBs) of the auditory filters is usually negligible