Auditory filter shapes derived with noise stimuli

Abstract

A wide-band noise having a deep notch with sharp edges was used to mask a tone [presented to human subjects]. The notch was centered on the tone, and threshold was measured as the width of the notch was increased from 0.0-0.8 times the tone frequency (0.5, 1.0 or 2.0 kHz). The spectrum level of the noise was 40 dB sound pressure level. If it is assumed that the auditory filter is reasonably symmetric at these intensities, then the shape of the filter centered on the tone can be estimated from the 1st derivative of the curve relating tone threshold to the width of the notch in the noise. The 3-dB bandwidths of the filters obtained were about 0.13 of their center frequency. In the region of the passband, the Gaussian curve provided a good approximation to the shape of the derived filters. The equivalent rectangular bandwidths of the Gaussian approximations were about 0.20 of their center frequency, which is comparable to the critical-band estimates of R. Zwicker, G. Flottorp and S.S. Stevens. The Gaussian approximation cannot be used outside the passband, because the tails of the derived filters do not fall as fast as the Gaussian curve.