Frequency selectivity for frequencies below 100 Hz: comparisons with mid-frequencies

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Signal Processing

Background:

• Understanding auditory filter shapes is crucial for explaining human sound perception.
• Low-frequency hearing is particularly complex due to physiological constraints.

Purpose of the Study:

• To characterize auditory filter shapes across a range of low signal frequencies (50-1000 Hz).
• To investigate the influence of masker spectrum level and middle-ear transfer function (METF) on these filters.
• To model auditory filters using a rounded-exponential model, incorporating METF effects.

Main Methods:

• Utilized the notched-noise method to derive auditory filter shapes.
• Measured auditory filters for signal frequencies (f(s)) from 50 to 1000 Hz.
• Employed a masker spectrum level (N(0)) of 50 dB, with additional measurements at 62 dB for lower frequencies (50-63 Hz).
• Fitted data using a rounded-exponential filter model, accounting for METF at low frequencies.

Main Results:

• Filter skirts were better defined at higher masker levels (62 dB) for very low signal frequencies.
• Filter sharpness and dynamic range decreased as signal frequency decreased.
• Equivalent rectangular bandwidth decreased down to 80 Hz, then increased below that.
• Middle-ear transfer function significantly influenced low-frequency filter skirts, especially below 50 Hz.
• Detection efficiency declined for frequencies between 100-500 Hz but slightly improved below 50 Hz.

Conclusions:

• Auditory filter characteristics are frequency-dependent, particularly at low frequencies.
• The middle-ear transfer function plays a critical role in shaping low-frequency auditory filters.
• The rounded-exponential model effectively describes auditory filters, especially when incorporating physiological constraints.