Effect of amplitude fluctuations on the loudness of low-frequency sounds

Abstract

The loudness of two-tone complexes (TTCs) with center frequencies (fc ) of 40, 63, 80, and 1000 Hz was matched with that of unmodulated tones (UTs). Frequency differences between the TTC components, corresponding to beat frequencies, fb , were 1, 2, 5, and 12 Hz. To compensate for the steep decline in hearing sensitivity below 100 Hz, prior to the loudness match, subjects adjusted the relative levels (ΔL) of the TTC components to give maximum beat perception. Twenty-four normal-hearing subjects were tested. The values of ΔL giving best beats were well predicted from the transfer function of the middle ear and the estimated shapes of the auditory filters, assuming that the auditory filter whose output dominated the beat percept was centered somewhat above fc . At the same root-mean-square level and independent of fc , TTCs were perceived as louder than UTs for fb ≤ 2 Hz, had roughly equal loudness to UTs for fb = 5 Hz, and were less loud than UTs for fb = 12 Hz. The similar pattern observed across fc suggests that the dependence of loudness on amplitude-fluctuation rate is determined by processes occurring at higher stages of the auditory system than the cochlea.The loudness of two-tone complexes (TTCs) with center frequencies (fc ) of 40, 63, 80, and 1000 Hz was matched with that of unmodulated tones (UTs). Frequency differences between the TTC components, corresponding to beat frequencies, fb , were 1, 2, 5, and 12 Hz. To compensate for the steep decline in hearing sensitivity below 100 Hz, prior to the loudness match, subjects adjusted the relative levels (ΔL) of the TTC components to give maximum beat perception. Twenty-four normal-hearing subjects were tested. The values of ΔL giving best beats were well predicted from the transfer function of the middle ear and the estimated shapes of the auditory filters, assuming that the auditory filter whose output dominated the beat percept was centered somewhat above fc . At the same root-mean-square level and independent of fc , TTCs were perceived as louder than UTs for fb ≤ 2 Hz, had roughly equal loudness to UTs for fb = 5 Hz, and were less loud than UTs for fb = 12 Hz. The similar pattern observed across fc s...