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 = 2 f 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.