TruEar

Besides binaural hearing (e.g., analysis and comparison of acoustic inputs in the brainstem), the human brain relies heavily on the acoustic characteristics of the outer ear for localization of sound, especially for elevation, and front/back localization. As a result, BTE users often have more trouble correctly localizing sound sources since the microphone is positioned above the ear, rather than in the ear canal. Siemens TruEar™ solves this problem by replicating the unique acoustic effects of the outer ear through processing of the input signal. The chart below illustrates how TruEar™ restores pinna effects. Due to the reflections and resonant characteristics of the human outer ear, frequencies above 1.5 kHz are amplified more for sounds from the front relative to other directions. As a result, a positive directivity index is obtained for these frequencies.

Directivity (as calculated by the DI) of the unaided open ear compared to a standard BTE (closed earmold) with an omnidirectional microphone and a BTE employing TruEar™ processing

In order to restore aided localization with BTEs, TruEar mimics the frequency-specific directivity of the human outer ear. This is accomplished by adjusting the hearing instrument's directional microphone system to match the directivity pattern of the pinna as closely as possible. As shown in the chart above, hearing instruments equipped with TruEar provide a very similar directivity at high frequencies to the unaided ear, meaning that the brain can easily use the spectral cues available to discriminate between signals coming from the front and from the back. This benefit of TruEar has been substantiated by research. Studies conducted at the National Acoustics Laboratory in Australia (Keidser et al. 2008) show that for all signals with components above 2 kHz, TruEar significantly reduces front/back confusions.

Note that hearing instruments with a microphone located close to the ear canal entrance (such as CICs) do not require TruEar as they can use the natural pinna effects.