On-Frequency Masking with Continuous Sinusoids

Abstract

The detectability of brief, 1000‐Hz sinusoids added in phase or in quadrature to a continuous tonal masker (pedestal) of the same frequency as the signal was examined in the presence of a continuous wide‐band noise. The effects of signal duration, shape of the signal's energy‐density spectrum, sound‐pressure level (SPL) of the pedestal, and noise spectrum level were investigated. For conditions in which the background noise level was low, two unusual phenomena were noted: (1) a complete absence of the customary trading relation between signal power and duration; and (2) an extremely shallow masking function relating signal SPL and pedestal level. These departures from the law of temporal integration and Weber's law are consistent with a simple filter model of the ear in which it is assumed that the location of the auditory filter is altered in response to changes in the parameters of the signal and masker. A basic assumption of the model is that the location of the filter is changed in order to maximize the ratio of signal energy to masker energy at the output of the filter. For detection of a tonal signal in the presence of another sinusoid, it appears that observers can listen at frequencies far removed from that of the signal, where signal energy is as much as 40 dB down from the peak.