Auditory filters at low-frequencies: Filter shape in the range 50 Hz to 1000 Hz

摘要

Prediction and asessment of low-frequency noise problems requires information about the auditory filter characteristics at low-frequencies. Unfortunately, data at low frequencies is scarce and practically no information exists for frequencies below 100 Hz. Extrapolation of previous results indicates the filter bandwidth would keep decreasing below 100 Hz, although at a low-rate and finally stabilizing. In this study, main auditory filter characteristics were obtained for center frequencies in the range 50 Hz to 1000 Hz. The notched-noise method was used, with the masker at moderate levels. Data from a total of 7 subjects is discussed. Considering the system as a whole (i.e. without removing the assumed middle-ear transfer function), the asymmetry of the auditory filter tended to change from steeper right-side slopes at 1000 Hz to steeper left-side slopes below 100 Hz. This effect was explained as due to increasing steepness at low-frequencies of the middle-ear high-pass filter. The dynamic range of the auditory filter steadily decreased with decreasing center frequency. The filter bandwidth at 63 Hz was about 36percent of the center frequency, its value being smaller than at 125 Hz in all cases, confirming expectations from extrapolating previous findings. However, at 50 Hz resuls were much more subject dependent: while a decrease in bandwidth was observed in some cases, in most cases selectivity was very small, i.e. the bandwidth was found to increase again.