Masking, Combination Tones, and Critical Bandwidth

Abstract

In experiments mapping pure-tone masked audiograms, in which the signal is either a pure tone or a narrow band of noise, a notch appears on the high-frequency side of the masker with a low point at a frequency one critical bandwidth from the masker frequency. This notch has been shown to be caused by the detection, on the lower-frequency side of the masker, of the combination tones that are produced by the addition of masker and signal. The same results are obtained when a very narrow band of noise masks a pure-tone signal. The implication that the same process that creates combination tones creates combination bands further supports other evidence as to the mechanical nature of combination tones. The immediate further implication bands or tones should therefore produce low-frequency masking effects in the same way that external stimuli do has been tested and confirmed over a wide range of intensities and frequency separations of the masking primaries. The latter have consisted of pairs of tones, tones plus narrow bands of noise, and pairs of narrow bands of noise. Some of the implications of these results for cochlear physics and critical bandwidth are outlined.