Aural distortion product fl + fh: growth rate and phase characteristics at different frequencies

This paper addresses the question of whether the nonlinear amplitude response of the ear depends only on stimulus level or on both level and frequency. The level of the quadratic distortion product fh + fl was estimated using the tone-on-tone masking paradigm under a 2AFC transformed UP-DOWN procedure. The higher frequency tone (fh) was maintained at 1.2 times the lower (fl = 250, 500, 1000, or 2000 HZ). Changes in the maximum and minimum threshold as maskee phase changes, [the monaural phase effect (MPE) amplitude], changes in the phase of the aural distortion product, and changes in the growth of the combination tone amplitude were examined as functions of primary frequency and level. The results indicate that MPE amplitude is simply a function of S/N ratio between the combination tone and the masking at that frequency. Distortion product phase varies over 360 degrees with respect to the primary tones and is unrelated to primary frequency or intensity. Within listeners the range of distortion product phase is more narrow (70-90 deg) at a single frequency. The absolute level of the summation tone does not correlate well with primary frequency and the growth rate of the combination tone varies with frequency and observers over a range of 1.1-2.3 dB/dB. The results suggest frequency independent nonlinearity when the ratio of primary frequencies is constant.