Frequency Dependency of Aural Difference Tones

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Abstract
Aural difference tones ranging from 125 to 3000 Hz were produced by primary tones between 1900 and 7700 Hz, wherein the normal threshold in decibels (re 0.0002 μbar) is relatively similar. Using difference tones as a masking stimulus for pure tones of the corresponding frequency, masked thresholds were obtained when the primary tones ranged in intensity from 60 to 110 dB SPL. The masking effect of the difference tones does not become apparent until the intensity of the primary tones reaches a level of 60 to 70 dB, after which there is a constant growth in the masking effect for each 10‐dB increase in the intensity of a given set of primary tones. Threshold shift due to the use of the difference tone as a masking stimulus is not dependent upon the frequency of the difference tone, but is a constant value for a given intensity and a group of primary tones. There is an inverse linear relationship between the intensity of the difference tone to that of the frequencies of the primary tones used to produce it. A maximum amount of threshold shift occurs in the vicinity of 650–1000 Hz, owing to resonance, and manifests itself when the primary tones have an intensity level of 80 dB or more.

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