Measurement of a Full 3D Set of HRTFs for In-Ear and Hearing Aid Microphones on a Head and Torso Simulator (HATS)

Abstract

The accurate reproduction of acoustic real-world environments is becoming of increasing importance in hearing device research and development. It is thereby often required to accurately predict the sound pressure at the microphones of ahearing device in asimulated or recorded acoustic environment. Forthat reason, an extensive set of head-related transfer functions (HRTFs)w as measured in free-field with ap air of behind-the-ear (BTE) hearing aids placed on aHead and Torso Simulator (HAT S).Transfer functions to the in-ear HATS microphones were also measured. As pherical head model wasa pplied to extend the useable frequencyr ange towards low frequencies. Special care wasgiven to preservethe phase properties of the measurements so that the HRTFs could be widely used in phase-sensitive technical applications, including the evaluation of spatial signal processing algorithms (i.e. directional microphones, beamformers)i nh earing devices and the evaluation of sound field resynthesis methods. The extended HRTF set can also be used for research in psychoacoustics. It is available for download at: http://www.nal.gov.au/download/HATS_BTE_hrirDatabase.zip.

Effects of Sensorineural Hearing Loss on Cortical Synchronization to Competing Speech during Selective Attention

“…The audio files were split into ϳ50-slong trials. The speech streams were spatially separated at Ϯ90°using non-individualized head related transfer functions (HRTFs) provided by Oreinos and Buchholz (2013). The audio files were low-pass filtered at 12 kHz using a second-order Butterworth filter to avoid excessive high-frequency amplification for subjects with low audiometric thresholds.…”

Evaluation of Loudspeaker-Based Virtual Sound Environments for Testing Directional Hearing Aids

“…Binaural technology has been employed (Van den Bogaert et al, 2008;Rychtáriková et al, 2009;Völk and Fastl, 2010;Mueller et al, 2012) as a means to introduce some realism into laboratory-based listening tests. However, presenting the auditory scene via headphones (a) requires-ideally individual-head-related transfer functions to the microphones of the HAs worn on the participant's head (Oreinos and Buchholz, 2013b), (b) precludes head movements (unless a head tracker is used), (c) disregards the acoustic path contribution (leakage) of the HA earmold, and (d) precludes the use of off-the-shelf or the participant's individual HAs.…”

Objective analysis of ambisonics for hearing aid applications: Effect of listener's head, room reverberation, and directional microphones

“…For that purpose, the DS and ERs were simply mapped to a discrete grid of auxiliary sources by shifting the direction of each individual image source to the direction of the closest available auxiliary source. A grid of N DE ¼ 1784 auxiliary sources was chosen, corresponding to the positions of the extended HRTF data-set recorded by Oreinos and Buchholz (2013), since these HRTFs were later used to derive ear and HA microphone signals (Sec. III C).…”

“…To evaluate the effect of HOA sound field reproduction on the benefit achieved with a directional HA microphone, the "effective directivity" of a directional microphone was estimated. A first order delay-and-subtract cardioid microphone output was derived by using measured front and rear BTE-HA-microphone TFs (Oreinos and Buchholz, 2013) to map the HOA loudspeaker signals to HA microphone signals. The directivity parameter (Kates, 2008, p. 84) was adjusted to a ¼ 0:575 to best approximate the directivity pattern (with the HAs placed on the HATS) of an ideal cardioid pattern.…”

“…where pðf ; h i ; d i Þ is the directional HA microphone output due to a unit-amplitude source located at ðh i ; d i Þ; p max ðf Þ is the maximum directional output [occurring at the look direction ðh max ; d max Þ], a i are the quadrature weights (normalized so that P I i¼1 a i ¼ 4p), and I is the number of applied quadrature points. Here, a regular grid of I ¼ 900 quadrature points (Fliege, 2007) was employed, after shifting each point to align with the closest available HRTF measurement position (Oreinos and Buchholz, 2013). The frequency-dependent look direction ðh max ; d max Þ was estimated only for the reference case and the same value was used to derive the DI for the HOA case.…”