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

Abstract

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 t•vo 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 sinusold with a frequency corresponding to the lower edge frequency of that band. This is referred to as the noise-tone maskeL 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.

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

“…Second, the masked thresholds for the higher center frequencies flattened off at values slightly above the measured absolute thresholds. This phenomenon has been observed previously ͑Glasberg et al, 1984͒, and it may reflect masking by distortion products produced by the upper band of noise ͑Glasberg and Moore, 1994;Moore et al, 1995͒. The first source of discrepancy may be related to the second; if the thresholds flatten off at large notch widths because of distortion products, then the flattening should not be regarded as arising from the filter shape per se.…”

Binaural notched-noise masking and auditory-filter shape

“…Figure 5 shows a comparison of the data of the present study to the data at 500 Hz with a comparable masker spectrum level. In addition, the data are compared to notched-noise data without binaural cues (Weber, 1977;Moore et al, 1995), the binaural masking release for broadband maskers without a notch, and thresholds in quiet.…”