Level-dependent IMD cancellation for single-transducer DPOAE measurement using a lookup-table method

Distortion product otoacoustic emissions (DPOAEs) are weak cochlear tones (f ₃ = 2f ₁ - f ₂) evoked by two primary tones (f ₁, f ₂) and used clinically to assess cochlear function. In practice, f ₁ and f ₂ are typically presented using two independent sound sources. This is because using one transducer to output both tones can generate intermodulation distortion (IMD) at the same frequency (f ₃) as the DPOAE due to transducer nonlinearity, which makes it difficult to distinguish measurement artifacts from biological emissions. As a result, DPOAE measurement is difficult with conventional earphones, which typically use one playback transducer per ear. Here, we describe a method that enables single-transducer DPOAE measurements by adding a cancellation tone at f ₃ and tuning its amplitude and phase (via a lock-in amplifier technique) to reduce IMD. Since IMD is level dependent and in-ear stimulus levels vary across ears (due to ear-canal acoustics), the required cancellation parameters are therefore stored in a level-specific lookup table (LUT). The proposed method:•Reduces IMD at the DPOAE frequency to enable single-transducer measurement.•Uses LUT parameters to handle level-dependent IMD.•Was validated on 40 ears against a two-transducer baseline.