Mechanism for bandpass frequency characteristic in distortion product otoacoustic emission generation

It is commonly observed that the levels of the 2 f 1 - f 2 and the other m f 1 - n f 2 ( m = n + 1 = integer ) distortion product otoacoustic emissions (DPOAEs) initially increase in level for fixed f 2 as f 1 → f 2 , starting at f 1 ⪡ f 2 , and then begin to decrease. When these DPOAE levels are plotted as a function of either the distortion product frequency ( f dp ) or f 2 ∕ f 1 the curve has an approximate bandpass shape. It has been hypothesized that this effect is due to (1) a second filter, (2) suppression of distortion generation by the primary tones, (3) reemission of distortion products from the distortion product place (on the basilar membrane), (4) the presence of an even order nonlinearity, and (5) cancellation of the DPOAE due to the vector addition of multiple sources of distortion product. In this study distortion products were produced with f 1 sweep conditions where there would be minimal vector cancellation of multiple DPOAE sources. It was observed that under this condition, there is no or minimal bandpass shape of the DPOAE generation curve. Therefore, the data support the hypothesis that the bandpass shape obtained with traditional f 1 sweeps is due to vector cancellation from multiple sources.