Intensities of aural difference tones

An aural difference tone attributed to nonlinearity of the ear was produced by the use of four pairs of pure tones, 750 and 1000, 1750 and 2000, 3750 and 4000, and 7750 and 8000 Hz. A binaural loudness balance, which demonstrated the difference tone produced by 750 and 1000 Hz at 100 dB, had a frequency equal to the numerical difference between the paired tones, and had an intensity of approximately 90 dB. Instrumentation difference tones were maintained at a level of at least 70 dB below that of the primary tones. The aural difference tone used as a monaural masking stimulus for a pure tone of 250 Hz produced more threshold shift when the pairs of tones were presented simultaneously than when each of the tones was presented individually. The masking effect of the aural difference tone is a function of the frequency and intensity of the primary tones. The spread of masking over a 2-oct range, 125–500 Hz, using 750 and 1000 Hz simultaneously as the masking stimulus, was similar to that of a 250-Hz pure-tone masking stimulus.