Comparison of Masking by Combination Bands and Bands of Noise of External Origin

Abstract

Combination bands generated by a pure tone and a narrow band of noise produce masking patterns in the frequency region where they occur. These patterns take the form of elevations that merge with, or stand in isolation from, the low-frequency side of the masked audiogram produced by the lower primary, depending on the separation of the bands from the primary. Masked audiograms produced by bands of external origin were also mapped. An “external” band was presented under two conditions: alone and then together with a more intense higher-frequency tone. Comparisons among conditions lead to these conclusions: (1) Addition of a higher-frequency more intense tone to a band of noise of external origin does not increase the masking maximum produced by the noise. This masking remains visible as an elevation on the low-frequency side of the masked audiogram produced by the tone—unless masking by the tone itself in the lower-frequency region of the noise exceeds the masking effect of the noise. (1) Consequently, it is inferred that masking produced by combination bands is also not significantly increased by the presence of the more intense higher-frequency primary stimuli. (3) Hence, by using signal-to-masker ratios obtained when narrow external bands are presented, one can estimate the intensity level of a combination band of comparable width from measurements of masked threshold in the region it occupies.