Adapting Hearing Devices to the Individual Ear Acoustics: Database and Target Response Correction Functions for Various Device Styles

Abstract

To achieve a natural sound quality when listening through hearing devices, the sound pressure at the eardrum should replicate that of the open ear, modified only by an insertion gain if desired. A target approximating this reference condition can be computed by applying an appropriate correction function to the pressure observed at the device microphone. Such Target Response Correction Functions (TRCF) can be defined based on the directionally dependent relative transfer function between the location of the hearing device microphone and the eardrum of the open ear. However, it is unclear how exactly the TRCF should be derived, and how large the benefit of individual, versus generic, correction is. We present measurements of Head-Related Transfer Functions (HRTF) at the eardrum and at 9 microphone locations of a comprehensive set of 5 hearing device styles, including 91 incidence directions, and recorded in 16 subjects and 2 dummy heads. Based on these HRTFs, individualized and generic TRCF were computed for frontal (referred to as free-field) and diffuse-field sound incidence. Spectral deviations between the computed target and listening with the open ear were evaluated using an auditory model and virtual acoustic scenes. Results indicate that a correction for diffuse-field incidence should be preferred over the free field, and individual correction functions result in notably reduced spectral deviations to open-ear listening, as compared with generic correction functions. These outcomes depend substantially on the specific device style. The HRTF database and derived TRCFs are publicly available.

Haptic sound-localisation for use in cochlear implant and hearing-aid users

“…Audio was first convolved with a head-related transfer function (HRTF) for the appropriate sound source location. The three-microphone behind-the-ear ("BTE_MultiCh") HRTFs from The Oldenburg Hearing Device HRTF Database 53 were used, in order to match a typical CI or hearing-aid signal. The signal from left and right ear channels were then resampled to a sampling frequency of 22,050 Hz.…”

Measurement of Head-Related Transfer Functions: A Review

“…Some studies measured HRTFs with microphones placed in various hearing aids [64,105,106], and the measurement results are useful for hearing instrument research, evaluating spectral distortions caused by hearing aids, and generating virtual sounds for hearing aid users, etc. Artificial heads (or dummy heads, head-and-torso systems) such as KEMAR (GRAS Sound & Vibration A/S, Holte, Denmark), Neumann KU-100 (Georg Neumann GmbH, Berlin, Germany), HMS IV (HEAD acoustics GmbH, Herzogenrath, Germany), and B & K 4128 (Brüel & Kjaer, Naerum, Denmark), are widely employed for measuring non-individual acoustic impulse responses and recording binaural sounds.…”

“…Note that the order of post-processing processes varies in the literature, and some processes may be performed several times. Moreover, some studies proposed to remove perceptually irrelevant components in HRTFs [106], and correct measurement errors caused by the equipment misalignment [137] and temperature fluctuations [174]. The important post-processing steps/methods are described below.…”

Localization Performance in a Binaural Real-Time Auralization System Extended to Research Hearing Aids

“…Since VAEs can be used as a test and training environment for users with HL (Cameron & Dillon, 2008, 2011, localization performance via HAs needs to be assessed separately. Denk et al (2018) objectively investigated monaural cue preservation across different HA device styles in generic and individual HRTFs by applying auditory models for sagittal plane localization (Baumgartner et al, 2014). Mueller et al (2012) tested localization ability of adults with normal hearing (NH) in realistic acoustic scenes when playing back simulated HA signals based on HARTFs over open-fit behind-theear (BTE) HAs.…”

“…Apart from dynamic cues, another crucial factor related to the occurrence of reversals is linked to the monaural cues of HRTFs (Iida et al, 2007;Shaw, 2007) which, if distorted, can potentially increase the reversal rates (Oberem et al, 2018;Wenzel et al, 1993). An aggravated effect can be expected if these cues are reduced or completely absent when presenting VSSs based on HARTFs when measured using BTE HA devices (Denk et al, 2018;Kayser et al, 2009;Pausch et al, 2018;Thiemann & van de Par, 2019). As regards Figure 2, a substantially more influential factor could have been a lack of low-frequency energy in condition RHA.…”